Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

• Disease Name: Hashimoto Encephalopathy
• MONDO ID: (if available)
• Category: Autoimmune

Research Objectives

Please provide a comprehensive research report on Hashimoto Encephalopathy covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

• What is the disease? Provide a concise overview.
• What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
• What are the common synonyms and alternative names?
• Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

• Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
• Risk Factors:

  Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases

• Genetic risk factors (causal variants, susceptibility loci, modifier genes)
• Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
• Protective Factors:

  Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases

• Genetic protective factors (protective variants, modifier alleles)
• Environmental protective factors (diet, lifestyle, exposures that reduce risk)
• Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

  Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

• Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

  Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene

• Pathogenic Variants:
• Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
• Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
• Variant type/class (missense, frameshift, nonsense, splice-site, structural)
• Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
• Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
• Functional consequences (loss of function, gain of function, dominant negative)
• Modifier Genes: Genes that modify disease severity or expression
• Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

  Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

• Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

  Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

• Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

  Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases

• Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

  Search first: CDC databases, WHO, PubMed, NHANES

• Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

  Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

• Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

  Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc

• Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

  Search first: Gene Ontology (GO), Reactome, KEGG, PubMed

• Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

  Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold

• Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

  Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA

• Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

  Search first: ImmPort, Immunome Database, IEDB, Gene Ontology

• Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

  Search first: PubMed, Gene Ontology, Reactome

• Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

  Search first: BRENDA, UniProt, KEGG, OMIM, PubMed

• Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

  Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

• Molecular Profiling (if available):
• Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
• Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
• Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
• Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
• Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
• Advanced Technologies (if applicable):
• Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
• Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
• Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
• Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

• Organ Level:
• Primary organs directly affected
• Secondary organ involvement (complications, secondary effects)
• Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

  Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT

• Tissue and Cell Level:
• Specific tissue types affected (epithelial, connective, muscle, nervous)
• Specific cell populations targeted (with Cell Ontology terms)

  Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB

• Subcellular Level:
• Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

  Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas

• Localization:
• Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
• Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

• Onset:
• Typical age of onset (congenital, pediatric, adult, geriatric)
• Onset pattern (acute, subacute, chronic, insidious)

  Search first: OMIM, Orphanet, HPO, PubMed

• Progression:
• Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
• Progression rate (rapid, slow, variable)
• Disease course pattern (episodic, relapsing-remitting, progressive, stable)
• Disease duration (self-limited, chronic lifelong)

  Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM

• Patterns:
• Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
• Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

• Epidemiology:
• Prevalence (cases per 100,000 at given time)
• Incidence (new cases per 100,000 per year)

  Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries

• For Genetic Etiology:
• Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
• Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
• Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
• Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
• Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
• Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
• Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
• Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
• Population Demographics:
• Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
• Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
• Geographic distribution of specific variants
• Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
• Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

• Clinical Tests:
• Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
• Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
• Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
• Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
• Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
• Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
• Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
• Genetic Testing:

  Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen

• Overview of recommended genetic testing approach
• Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
• Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
• Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
• Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
• Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
• Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
• FISH > Search first: ClinVar, cytogenetics databases, PubMed
• Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
• Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
• Omics-Based Diagnostics (if applicable):
• RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
• Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
• Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
• Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
• Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
• Clinical Criteria:
• Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
• Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
• Screening:
• Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

• Survival and Mortality:
• Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
• Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
• Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
• Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
• Morbidity and Function:
• Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
• Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
• Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
• Disease Course:
• Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
• Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
• Prediction:
• Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
• Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

• Pharmacotherapy:
• Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
• Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
• Advanced Therapeutics:
• Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
• Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
• RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
• Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
• Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
• Surgical and Interventional:
• Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
• Supportive and Rehabilitative:
• Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
• Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
• Experimental:
• Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
• Treatment Outcomes:
• Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
• Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
• Treatment Strategy:
• Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
• Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
• Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest MAXO (Medical Action Ontology) terms where applicable.

13. Prevention

• Prevention Levels:
• Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
• Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
• Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
• Immunization: Vaccine strategies (if applicable)

  Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database

• Screening and Early Detection:
• Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
• Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
• Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
• Behavioral Interventions: Lifestyle modifications to reduce risk

  Search first: CDC, WHO, behavioral intervention databases, Cochrane Library

• Counseling: Genetic counseling (risk assessment, family planning guidance)

  Search first: NSGC resources, ACMG guidelines, GeneReviews

• Public Health:
• Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
• Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
• Prophylaxis: Preventive medications or procedures

  Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

• Taxonomy: Species affected (with NCBI Taxon identifiers)

  Search first: NCBI Taxonomy

• Breed: Specific breeds affected (with VBO identifiers if applicable)

  Search first: VBO (Vertebrate Breed Ontology)

• Gene: Orthologous genes in other species (with NCBI Gene IDs)

  Search first: NCBI Gene

• Natural Disease:
• Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
• Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
• Comparative Biology:
• Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
• Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
• Transmission (if applicable):
• Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
• Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

• Model Types:
• Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
• Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
• Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
• Genetic Models:
• Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
• Model Characteristics:
• Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
• Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
• Applications:
• Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
• Resources:
• Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

• Cite primary literature (PMID preferred) for all mechanistic and clinical claims
• Prioritize recent reviews and landmark papers
• Include direct quotes from abstracts where possible to support key statements
• Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, MAXO, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (MAXO terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Hashimoto Encephalopathy (HE) / Steroid‑Responsive Encephalopathy Associated with Autoimmune Thyroiditis (SREAT)

Executive summary

Hashimoto encephalopathy (HE), also called steroid‑responsive encephalopathy associated with autoimmune thyroiditis (SREAT), is a controversial, exclusion-based syndrome characterized by subacute encephalopathy with neuropsychiatric and/or seizure manifestations in the context of thyroid autoantibodies and frequent—but not universal—immunotherapy responsiveness. Modern expert frameworks stress that thyroid antibodies are common in the population and not disease-specific, so diagnosis requires careful exclusion of mimics and evaluation for neuronal autoantibodies and objective CNS inflammation. In a large tertiary referral series of 144 thyroid-antibody–positive patients referred as suspected HE/SREAT, 73% ultimately had an alternative diagnosis, underscoring a major real-world risk of misdiagnosis. (valenciasanchez2021braindysfunctionand pages 1-2, valenciasanchez2021braindysfunctionand pages 14-15)

1. Disease information

1.1 Definition and overview

Graus et al. (Lancet Neurology, Apr 2016) position Hashimoto’s encephalopathy/SREAT as an entity that should be classified as probable autoimmune encephalitis only when a structured set of criteria are met and alternative causes are reasonably excluded. Their Panel 6 includes encephalopathy with seizures/myoclonus/hallucinations/stroke‑like episodes, thyroid disease, normal/nonspecific MRI, serum thyroid antibodies, absence of well-characterized neuronal antibodies, and exclusion of alternative causes. (graus2016aclinicalapproach pages 15-17)

A 2023 review describes HE/SREAT as a syndrome of “altered mental status, confusion, hallucinations, delusions and sometimes seizures” associated with elevated anti‑thyroid antibodies and usual steroid responsiveness, while emphasizing uncertain pathogenesis and the need to exclude other encephalitides. (chaudhuri2023hashimoto’sencephalopathycase pages 1-2)

Evidence source type: predominantly human case reports/series and retrospective cohorts; limited high-quality prospective data and no disease‑specific biomarker. (pempera2024difficultiesinthe pages 1-2)

1.2 Synonyms / alternative names

• Hashimoto encephalopathy (HE) (chaudhuri2023hashimoto’sencephalopathycase pages 1-2)
• Steroid‑responsive encephalopathy associated with autoimmune thyroiditis (SREAT) (graus2016aclinicalapproach pages 15-17)
• (Sometimes used) “steroid‑responsive autoimmune encephalopathies” concept to avoid thyroid‑centric over-attribution (review perspective). (manocchio2025hashimoto’sencephalopathyclinical pages 11-13)

1.3 Key identifiers (knowledge-base mapping)

The retrieved full-text evidence did not provide explicit mappings to MONDO, Orphanet (ORPHAcode), OMIM, MeSH, ICD‑10, or ICD‑11 for HE/SREAT. Therefore these identifiers cannot be asserted from the current tool evidence set and should be populated from external terminologies (e.g., MONDO/Orphanet browsers) outside this run.

2. Etiology

2.1 Primary causal factors

Current understanding: HE/SREAT is presumed autoimmune but remains mechanistically uncertain. - A 2024 systematic and critical review states HE is “poorly understood,” lacks a specific marker, and its pathogenesis remains unclear; multiple controversies argue against simple antibody causality (e.g., no correlation between antibody levels and symptom severity). (pempera2024difficultiesinthe pages 1-2) - Graus et al. emphasize thyroid antibodies lack disease specificity and are present in a substantial fraction of healthy individuals. (graus2016aclinicalapproach pages 15-17)

2.2 Risk factors (evidence-limited)

• Sex/age: prior compiled series show female predominance (e.g., 73% female in a 251-case literature synthesis). (laurent2016steroidresponsiveencephalopathyassociated pages 2-2)
• Autoimmune background: suspected/true autoimmune CNS cases more often had other autoimmune disorders in a large referral cohort. (valenciasanchez2021braindysfunctionand pages 4-5)
• Thyroid autoimmunity: thyroid antibody positivity is necessary in most proposed criteria, but is not specific for HE/SREAT. (graus2016aclinicalapproach pages 15-17, valenciasanchez2021braindysfunctionand pages 14-15)

2.3 Protective factors

No specific protective genetic or environmental factors were identified in the retrieved evidence.

2.4 Gene–environment interactions

Not established in the retrieved evidence.

3. Phenotypes (clinical features)

3.1 Core phenotype spectrum

In a Thailand tertiary center cohort of 13 HE patients (BMC Neurology, Sep 2023), frequencies illustrate typical manifestations: cognitive impairment (76.9%), clouding of consciousness (46.2%), ataxia (46.2%), seizures (38.5%) including status epilepticus (23.1%), sleep disturbance (38.5%), behavior change (30.8%), and neuropsychiatric symptoms such as visual hallucinations (30.8%) and mood disturbance (23.1%). (dumrikarnlert2023clinicalpresentationsand pages 2-4)

A large literature synthesis of 251 cases (Autoimmunity Reviews, Dec 2016) reports common presentations: seizures (47%), confusion (46%), memory impairment (43%), speech disorder (37%), gait disturbance (27%), persecutory delusions (25%), myoclonus (22%), coma (15%), and depression (12%). (laurent2016steroidresponsiveencephalopathyassociated pages 2-2)

3.2 Course and onset

• Subacute onset is common and often operationalized as <3 months in autoimmune encephalitis criteria frameworks. (graus2016aclinicalapproach pages 4-6)
• In the Mayo referral cohort, subacute onset strongly distinguished autoimmune CNS disorders from alternative diagnoses (82.1% vs 27.6%). (valenciasanchez2021braindysfunctionand pages 4-5)

3.3 Quality of life / functional impact

Functional impairment is substantial in true autoimmune CNS cases and may be misattributed in others; clinical outcomes in Dumrikarnlert et al. were evaluated with modified Rankin Scale (mRS)–based definitions of improvement. (dumrikarnlert2023clinicalpresentationsand pages 1-2)

3.4 Suggested HPO terms (examples)

(Provided as ontology suggestions for knowledge-base use; not asserted as exclusive) - Encephalopathy (HP:0001298) - Cognitive impairment (HP:0100543) - Confusion (HP:0001289) - Seizure (HP:0001250) - Status epilepticus (HP:0002133) - Ataxia (HP:0001251) - Myoclonus (HP:0001336) - Hallucinations (HP:0000738) - Delusions (HP:0000746) - Sleep disturbance / insomnia (HP:0100785 / HP:0002360)

4. Genetic / molecular information

4.1 Causal genes and variants

No monogenic causal genes or pathogenic germline variants for HE/SREAT were identified in the retrieved evidence; major criteria and modern series conceptualize HE/SREAT as an autoimmune encephalopathy associated with thyroid autoimmunity rather than a Mendelian disorder. (graus2016aclinicalapproach pages 15-17, pempera2024difficultiesinthe pages 1-2)

4.2 Proposed autoantibodies and molecular markers

• Thyroid antibodies: anti‑TPO and anti‑thyroglobulin antibodies are part of diagnostic criteria but are poorly specific and may indicate general autoimmunity rather than causality. (graus2016aclinicalapproach pages 15-17, valenciasanchez2021braindysfunctionand pages 14-15)
• Anti‑NH2‑terminal α‑enolase (anti‑NAE): proposed but reported as non‑specific (and not useful in at least one modern series; also highlighted as non‑specific in a 2024 systematic review). (pempera2024difficultiesinthe pages 1-2, graus2016aclinicalapproach pages 15-17)

5. Environmental information

No specific environmental toxins/exposures or infectious triggers were established in the retrieved evidence. Because HE/SREAT is operationally a diagnosis of exclusion, infection-triggered encephalitis and toxic-metabolic encephalopathies are key differentials to rule out rather than established triggers. (graus2016aclinicalapproach pages 4-6, graus2016aclinicalapproach pages 15-17)

6. Mechanism / pathophysiology

6.1 Current hypotheses

Mechanisms remain uncertain; proposed contributors include autoimmune inflammation, possible vasculitis, cerebral hypoperfusion, and edema. - A 2024 systematic review underscores controversy: no correlation between antibody levels and symptom severity; anti‑TPO may help rule out HE if negative but cannot confirm it; anti‑NAE is non-specific. (pempera2024difficultiesinthe pages 1-2) - A 2023 review states available evidence points to autoimmune etiology via vasculitis or inflammatory processes, but thyroid antibodies are non-specific and may act as markers rather than pathogenic effectors. (chaudhuri2023hashimoto’sencephalopathycase pages 1-2)

6.2 Causal chain (working model)

1) Background thyroid autoimmunity and systemic autoimmune propensity (marker: anti‑TPO/anti‑Tg) (graus2016aclinicalapproach pages 15-17) 2) CNS immune activation (subset show CSF inflammatory changes, EEG/MRI abnormalities) (valenciasanchez2021braindysfunctionand pages 7-9) 3) Network dysfunction manifesting as encephalopathy, seizures/NCSE, neuropsychiatric symptoms (dumrikarnlert2023clinicalpresentationsand pages 2-4, lee2024clinicalanddiagnostic pages 1-2) 4) Clinical improvement in many patients after immunotherapy (steroids ± other therapies), supporting immune mediation in true cases (dumrikarnlert2023clinicalpresentationsand pages 2-4, lee2024clinicalanddiagnostic pages 1-2)

6.3 Suggested GO and Cell Ontology (CL) terms

(Heuristic mapping for knowledge-base representation) - GO:0006954 inflammatory response - GO:0002376 immune system process - GO:0006955 immune response - GO:0002682 regulation of immune system process - CL:0000540 neuron (end-organ affected) - CL:0000129 microglial cell (candidate CNS immune effector) - CL:0000084 T cell (systemic autoimmune contributor) - CL:0000236 B cell / plasma cell (autoantibody production)

7. Anatomical structures affected

Primary system: central nervous system. - Brain dysfunction/encephalopathy is the defining manifestation. (graus2016aclinicalapproach pages 15-17) - Nonspecific white‑matter MRI changes are reported in cohorts. (dumrikarnlert2023clinicalpresentationsand pages 4-6)

Suggested UBERON terms: - UBERON:0000955 brain - UBERON:0001017 central nervous system

8. Temporal development

• Onset pattern: commonly subacute; in Dumrikarnlert et al. most patients had onset within <3 months. (dumrikarnlert2023clinicalpresentationsand pages 1-2)
• Course: relapsing course is reported. A 2024 systematic review estimated relapse after glucocorticoids at 31.67%. (pempera2024difficultiesinthe pages 1-2)

9. Inheritance and population

9.1 Epidemiology

Reliable population incidence/prevalence is limited; many publications are case reports/series. - The 2024 systematic review cites an estimated adult prevalence around 2.1 per 100,000 (secondary estimate) and emphasizes limited high-quality evidence. (pempera2024difficultiesinthe pages 1-2)

9.2 Sex ratio and demographics

• A 251-case literature synthesis reported 73% female and median age 52 years. (laurent2016steroidresponsiveencephalopathyassociated pages 2-2)

10. Diagnostics

10.1 Diagnostic criteria (expert framework)

Graus et al. Panel 6 (2016) diagnostic elements for Hashimoto’s encephalopathy/SREAT (probable autoimmune encephalitis classification) include: 1) Encephalopathy with seizures/myoclonus/hallucinations/stroke‑like episodes 2) Subclinical or mild thyroid disease (usually hypothyroidism) 3) Normal or nonspecific brain MRI 4) Serum thyroid antibodies (TPO/Tg) 5) Absence of well‑characterised neuronal antibodies in serum and CSF 6) Reasonable exclusion of alternative causes (graus2016aclinicalapproach pages 15-17)

Visual evidence: Dumrikarnlert et al. provide exclusion-based HE diagnostic criteria in Table 3 (cropped table image). (dumrikarnlert2023clinicalpresentationsand media d790e71b)

10.2 Laboratory tests / biomarkers

• Thyroid antibodies: anti‑TPO/anti‑Tg positive in HE criteria but not specific; thyroid antibodies occur in ~13% of healthy individuals (and more with age/sex effects), limiting confirmatory value. (graus2016aclinicalapproach pages 15-17, valenciasanchez2021braindysfunctionand pages 14-15)
• CSF: in Dumrikarnlert et al., CSF protein elevation occurred in 46.2% and pleocytosis in 15.4%. (dumrikarnlert2023clinicalpresentationsand pages 4-6)
• EEG: often abnormal in true autoimmune CNS cases; in Lee et al. 2024, NCSE was identified in 6 patients and was intractable to antiepileptic drugs. (lee2024clinicalanddiagnostic pages 1-2)

10.3 Imaging

• MRI is frequently normal or nonspecific; Dumrikarnlert et al. reported nonspecific white matter changes in all cases (by criteria) and note that many reported cases can have normal MRI. (dumrikarnlert2023clinicalpresentationsand pages 4-6)

10.4 Differential diagnosis and misdiagnosis risk (real-world implementation)

A key modern practice point is that many patients referred as “HE/SREAT” have other diagnoses. - In a Mayo Clinic series of 144 thyroid‑antibody–positive referrals for suspected HE/SREAT, only 27% were diagnosed with an autoimmune CNS disorder; 73% had alternative diagnoses (functional neurological disorder, neurodegeneration, primary psychiatric disease, etc.). (valenciasanchez2021braindysfunctionand pages 1-2) - Objective abnormalities (MRI/EEG/CSF inflammation) were more frequent in autoimmune CNS cases than in alternative diagnoses. (valenciasanchez2021braindysfunctionand pages 7-9)

11. Outcomes / prognosis

• Many true cases improve with immunotherapy, but non-response and relapse are common.
• Systematic review estimate: glucocorticoid effectiveness 60.94% with relapse 31.67%. (pempera2024difficultiesinthe pages 1-2)
• In Dumrikarnlert et al. (2023), among 12 treated with corticosteroids, 75% had marked improvement; 1 untreated patient died. (dumrikarnlert2023clinicalpresentationsand pages 2-4)

12. Treatment

12.1 First-line immunotherapy (current practice)

• Corticosteroids are widely considered first-line and are embedded in the historical concept of “steroid responsiveness.” (graus2016aclinicalapproach pages 15-17)
• Real-world cohort data: Dumrikarnlert et al. show marked improvement in 75% after corticosteroids among treated patients. (dumrikarnlert2023clinicalpresentationsand pages 2-4)
• Lee et al. report 90.5% good outcomes in immunosuppressant-treated probable HE patients. (lee2024clinicalanddiagnostic pages 1-2)

12.2 Steroid-sparing / second-line therapies

Evidence in the retrieved set is mainly review-level; IVIG and plasmapheresis are discussed as alternatives for non-responders in contemporary reviews. (manocchio2025hashimoto’sencephalopathyclinical pages 1-2)

12.3 Suggested MAXO terms (examples)

• Glucocorticoid therapy (MAXO:0000064)
• Intravenous immunoglobulin therapy (MAXO:0000747)
• Therapeutic plasmapheresis (MAXO:0000127)
• Immunosuppressive agent therapy (MAXO:0000106)
• Antiseizure medication therapy (MAXO:0000177)

13. Prevention

No established primary prevention exists in the retrieved evidence. The most evidence-supported “preventive” strategy is preventing morbidity from diagnostic delay/misdiagnosis by applying rigorous autoimmune encephalitis criteria, performing neuronal antibody testing, and requiring objective CNS inflammatory evidence when possible. (valenciasanchez2021braindysfunctionand pages 1-2, graus2016aclinicalapproach pages 15-17)

14. Other species / natural disease

No naturally occurring veterinary analogs were identified in the retrieved evidence.

15. Model organisms

No validated model organism systems specific to HE/SREAT were identified in the retrieved evidence.

Recent developments (2023–2024 focus)

Table: This table summarizes the most informative recent and landmark studies on Hashimoto encephalopathy or SREAT, emphasizing diagnostic criteria, test findings, treatment outcomes, and controversies. It is useful for quickly comparing how modern studies refine or challenge the traditional HE or SREAT concept.

Key advances in 2023–2024 center on (i) quantifying real-world presentation and response in modern tertiary cohorts and (ii) emphasizing diagnostic stringency to avoid thyroid-antibody–driven overdiagnosis. Dumrikarnlert et al. (Sep 2023) provide detailed phenotype frequencies and steroid response in a screened encephalopathy cohort, while Lee et al. (Jun 2024) report high rates of probable HE among antithyroid-antibody–tested unexplained encephalopathy presentations and highlight NCSE refractory to antiseizure medications as an important treatable manifestation. A 2024 systematic review (Pempera et al.) provides pooled estimates of glucocorticoid effectiveness and relapse, but also underscores limited high-quality evidence and lack of specific biomarkers. (dumrikarnlert2023clinicalpresentationsand pages 2-4, lee2024clinicalanddiagnostic pages 1-2, pempera2024difficultiesinthe pages 1-2)

Direct abstract-supported quotes (for knowledge-base evidence items)

• Pempera et al. (IJMS, Jun 2024) conclude: “there is no specific HE marker” and report “The effectiveness of glucocorticoid therapy is 60.94%, although relapse occurs in 31.67% of patients following the treatment.” (pempera2024difficultiesinthe pages 1-2)
• Dumrikarnlert et al. (BMC Neurology, Sep 2023) report common presentations and outcomes including: “Clinical presentations included cognitive impairment (76.9%)…” and among steroid-treated patients “9 (75%) had marked improvement…” (dumrikarnlert2023clinicalpresentationsand pages 1-2)
• Valencia-Sanchez et al. (Brain Communications, 2021) report: “73% of the patients referred with suspected Hashimoto encephalopathy had an alternative non-immune-mediated diagnosis” and that thyroid antibodies are common and “of little value” for diagnosing autoimmune encephalopathy without objective findings. (valenciasanchez2021braindysfunctionand pages 1-2)

URLs and publication dates (selected)

• Graus et al., Apr 2016, The Lancet Neurology: https://doi.org/10.1016/S1474-4422(15)00401-9 (graus2016aclinicalapproach pages 15-17)
• Laurent et al., Dec 2016, Autoimmunity Reviews: https://doi.org/10.1016/j.autrev.2016.09.008 (laurent2016steroidresponsiveencephalopathyassociated pages 2-2)
• Valencia-Sanchez et al., Jan 2021, Brain Communications: https://doi.org/10.1093/braincomms/fcaa233 (valenciasanchez2021braindysfunctionand pages 1-2)
• Chaudhuri et al., Feb 2023, Current Neurology and Neuroscience Reports: https://doi.org/10.1007/s11910-023-01255-5 (chaudhuri2023hashimoto’sencephalopathycase pages 1-2)
• Dumrikarnlert et al., Sep 2023, BMC Neurology: https://doi.org/10.1186/s12883-023-03305-4 (dumrikarnlert2023clinicalpresentationsand pages 1-2)
• Lee et al., Jun 2024, Acta Neurologica Belgica: https://doi.org/10.1007/s13760-024-02520-1 (lee2024clinicalanddiagnostic pages 1-2)
• Pempera et al., Jun 2024, International Journal of Molecular Sciences: https://doi.org/10.3390/ijms25137101 (pempera2024difficultiesinthe pages 1-2)

References

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2. (valenciasanchez2021braindysfunctionand pages 14-15): Cristina Valencia-Sanchez, Sean J Pittock, Carolyn Mead-Harvey, Divyanshu Dubey, Eoin P Flanagan, Sebastian Lopez-Chiriboga, Max R Trenerry, Nicholas L Zalewski, Anastasia Zekeridou, and Andrew McKeon. Brain dysfunction and thyroid antibodies: autoimmune diagnosis and misdiagnosis. Brain Communications, Jan 2021. URL: https://doi.org/10.1093/braincomms/fcaa233, doi:10.1093/braincomms/fcaa233. This article has 59 citations and is from a peer-reviewed journal.

3. (graus2016aclinicalapproach pages 15-17): Francesc Graus, Maarten J Titulaer, Ramani Balu, Susanne Benseler, Christian G Bien, Tania Cellucci, Irene Cortese, Russell C Dale, Jeffrey M Gelfand, Michael Geschwind, Carol A Glaser, Jerome Honnorat, Romana Höftberger, Takahiro Iizuka, Sarosh R Irani, Eric Lancaster, Frank Leypoldt, Harald Prüss, Alexander Rae-Grant, Markus Reindl, Myrna R Rosenfeld, Kevin Rostásy, Albert Saiz, Arun Venkatesan, Angela Vincent, Klaus-Peter Wandinger, Patrick Waters, and Josep Dalmau. A clinical approach to diagnosis of autoimmune encephalitis. The Lancet Neurology, 15:391-404, Apr 2016. URL: https://doi.org/10.1016/s1474-4422(15)00401-9, doi:10.1016/s1474-4422(15)00401-9. This article has 4832 citations and is from a highest quality peer-reviewed journal.

4. (chaudhuri2023hashimoto’sencephalopathycase pages 1-2): Jasodhara Chaudhuri, Angshuman Mukherjee, and Ambar Chakravarty. Hashimoto’s encephalopathy: case series and literature review. Current Neurology and Neuroscience Reports, 23:167-175, Feb 2023. URL: https://doi.org/10.1007/s11910-023-01255-5, doi:10.1007/s11910-023-01255-5. This article has 78 citations and is from a domain leading peer-reviewed journal.

5. (pempera2024difficultiesinthe pages 1-2): Nikola Pempera, Miłosz Miedziaszczyk, and Katarzyna Lacka. Difficulties in the diagnostics and treatment of hashimoto’s encephalopathy—a systematic and critical review. International Journal of Molecular Sciences, 25:7101, Jun 2024. URL: https://doi.org/10.3390/ijms25137101, doi:10.3390/ijms25137101. This article has 13 citations.

6. (manocchio2025hashimoto’sencephalopathyclinical pages 11-13): Nicola Manocchio, Valerio Massimo Magro, Livio Massaro, Andrea Sorbino, Concetta Ljoka, and Calogero Foti. Hashimoto’s encephalopathy: clinical features, therapeutic strategies, and rehabilitation approaches. Biomedicines, 13:726, Mar 2025. URL: https://doi.org/10.3390/biomedicines13030726, doi:10.3390/biomedicines13030726. This article has 12 citations.

7. (laurent2016steroidresponsiveencephalopathyassociated pages 2-2): Charlotte Laurent, Jean Capron, Bluenn Quillerou, Guy Thomas, Sonia Alamowitch, Olivier Fain, and Arsène Mekinian. Steroid-responsive encephalopathy associated with autoimmune thyroiditis (sreat): characteristics, treatment and outcome in 251 cases from the literature. Autoimmunity reviews, 15 12:1129-1133, Dec 2016. URL: https://doi.org/10.1016/j.autrev.2016.09.008, doi:10.1016/j.autrev.2016.09.008. This article has 243 citations and is from a peer-reviewed journal.

8. (valenciasanchez2021braindysfunctionand pages 4-5): Cristina Valencia-Sanchez, Sean J Pittock, Carolyn Mead-Harvey, Divyanshu Dubey, Eoin P Flanagan, Sebastian Lopez-Chiriboga, Max R Trenerry, Nicholas L Zalewski, Anastasia Zekeridou, and Andrew McKeon. Brain dysfunction and thyroid antibodies: autoimmune diagnosis and misdiagnosis. Brain Communications, Jan 2021. URL: https://doi.org/10.1093/braincomms/fcaa233, doi:10.1093/braincomms/fcaa233. This article has 59 citations and is from a peer-reviewed journal.

9. (dumrikarnlert2023clinicalpresentationsand pages 2-4): Chaisak Dumrikarnlert, Smathorn Thakolwiboon, and Vorapun Senanarong. Clinical presentations and treatment outcomes of hashimoto encephalopathy at siriraj hospital – thailand’s largest national tertiary referral center. BMC Neurology, Sep 2023. URL: https://doi.org/10.1186/s12883-023-03305-4, doi:10.1186/s12883-023-03305-4. This article has 14 citations and is from a peer-reviewed journal.

10. (graus2016aclinicalapproach pages 4-6): Francesc Graus, Maarten J Titulaer, Ramani Balu, Susanne Benseler, Christian G Bien, Tania Cellucci, Irene Cortese, Russell C Dale, Jeffrey M Gelfand, Michael Geschwind, Carol A Glaser, Jerome Honnorat, Romana Höftberger, Takahiro Iizuka, Sarosh R Irani, Eric Lancaster, Frank Leypoldt, Harald Prüss, Alexander Rae-Grant, Markus Reindl, Myrna R Rosenfeld, Kevin Rostásy, Albert Saiz, Arun Venkatesan, Angela Vincent, Klaus-Peter Wandinger, Patrick Waters, and Josep Dalmau. A clinical approach to diagnosis of autoimmune encephalitis. The Lancet Neurology, 15:391-404, Apr 2016. URL: https://doi.org/10.1016/s1474-4422(15)00401-9, doi:10.1016/s1474-4422(15)00401-9. This article has 4832 citations and is from a highest quality peer-reviewed journal.

11. (dumrikarnlert2023clinicalpresentationsand pages 1-2): Chaisak Dumrikarnlert, Smathorn Thakolwiboon, and Vorapun Senanarong. Clinical presentations and treatment outcomes of hashimoto encephalopathy at siriraj hospital – thailand’s largest national tertiary referral center. BMC Neurology, Sep 2023. URL: https://doi.org/10.1186/s12883-023-03305-4, doi:10.1186/s12883-023-03305-4. This article has 14 citations and is from a peer-reviewed journal.

12. (valenciasanchez2021braindysfunctionand pages 7-9): Cristina Valencia-Sanchez, Sean J Pittock, Carolyn Mead-Harvey, Divyanshu Dubey, Eoin P Flanagan, Sebastian Lopez-Chiriboga, Max R Trenerry, Nicholas L Zalewski, Anastasia Zekeridou, and Andrew McKeon. Brain dysfunction and thyroid antibodies: autoimmune diagnosis and misdiagnosis. Brain Communications, Jan 2021. URL: https://doi.org/10.1093/braincomms/fcaa233, doi:10.1093/braincomms/fcaa233. This article has 59 citations and is from a peer-reviewed journal.

13. (lee2024clinicalanddiagnostic pages 1-2): Jung-Ju Lee, Soo-Min Park, Kyung-Il Park, Kyusik Kang, Woong Woo Lee, Byung Kun Kim, Yong Soo Kim, and Ilhan Yoo. Clinical and diagnostic characteristics of hashimoto’s encephalopathy: a single-center, retrospective study. Acta Neurologica Belgica, 124:1839-1846, Jun 2024. URL: https://doi.org/10.1007/s13760-024-02520-1, doi:10.1007/s13760-024-02520-1. This article has 2 citations and is from a peer-reviewed journal.

14. (dumrikarnlert2023clinicalpresentationsand pages 4-6): Chaisak Dumrikarnlert, Smathorn Thakolwiboon, and Vorapun Senanarong. Clinical presentations and treatment outcomes of hashimoto encephalopathy at siriraj hospital – thailand’s largest national tertiary referral center. BMC Neurology, Sep 2023. URL: https://doi.org/10.1186/s12883-023-03305-4, doi:10.1186/s12883-023-03305-4. This article has 14 citations and is from a peer-reviewed journal.

15. (dumrikarnlert2023clinicalpresentationsand media d790e71b): Chaisak Dumrikarnlert, Smathorn Thakolwiboon, and Vorapun Senanarong. Clinical presentations and treatment outcomes of hashimoto encephalopathy at siriraj hospital – thailand’s largest national tertiary referral center. BMC Neurology, Sep 2023. URL: https://doi.org/10.1186/s12883-023-03305-4, doi:10.1186/s12883-023-03305-4. This article has 14 citations and is from a peer-reviewed journal.

16. (manocchio2025hashimoto’sencephalopathyclinical pages 1-2): Nicola Manocchio, Valerio Massimo Magro, Livio Massaro, Andrea Sorbino, Concetta Ljoka, and Calogero Foti. Hashimoto’s encephalopathy: clinical features, therapeutic strategies, and rehabilitation approaches. Biomedicines, 13:726, Mar 2025. URL: https://doi.org/10.3390/biomedicines13030726, doi:10.3390/biomedicines13030726. This article has 12 citations.

17. (dumrikarnlert2023clinicalpresentationsand pages 6-7): Chaisak Dumrikarnlert, Smathorn Thakolwiboon, and Vorapun Senanarong. Clinical presentations and treatment outcomes of hashimoto encephalopathy at siriraj hospital – thailand’s largest national tertiary referral center. BMC Neurology, Sep 2023. URL: https://doi.org/10.1186/s12883-023-03305-4, doi:10.1186/s12883-023-03305-4. This article has 14 citations and is from a peer-reviewed journal.

18. (lee2024clinicalanddiagnostic pages 6-8): Jung-Ju Lee, Soo-Min Park, Kyung-Il Park, Kyusik Kang, Woong Woo Lee, Byung Kun Kim, Yong Soo Kim, and Ilhan Yoo. Clinical and diagnostic characteristics of hashimoto’s encephalopathy: a single-center, retrospective study. Acta Neurologica Belgica, 124:1839-1846, Jun 2024. URL: https://doi.org/10.1007/s13760-024-02520-1, doi:10.1007/s13760-024-02520-1. This article has 2 citations and is from a peer-reviewed journal.

19. (chaudhuri2023hashimoto’sencephalopathycase pages 6-7): Jasodhara Chaudhuri, Angshuman Mukherjee, and Ambar Chakravarty. Hashimoto’s encephalopathy: case series and literature review. Current Neurology and Neuroscience Reports, 23:167-175, Feb 2023. URL: https://doi.org/10.1007/s11910-023-01255-5, doi:10.1007/s11910-023-01255-5. This article has 78 citations and is from a domain leading peer-reviewed journal.

20. (valenciasanchez2021braindysfunctionand pages 13-14): Cristina Valencia-Sanchez, Sean J Pittock, Carolyn Mead-Harvey, Divyanshu Dubey, Eoin P Flanagan, Sebastian Lopez-Chiriboga, Max R Trenerry, Nicholas L Zalewski, Anastasia Zekeridou, and Andrew McKeon. Brain dysfunction and thyroid antibodies: autoimmune diagnosis and misdiagnosis. Brain Communications, Jan 2021. URL: https://doi.org/10.1093/braincomms/fcaa233, doi:10.1093/braincomms/fcaa233. This article has 59 citations and is from a peer-reviewed journal.

21. (valenciasanchez2021braindysfunctionand pages 15-16): Cristina Valencia-Sanchez, Sean J Pittock, Carolyn Mead-Harvey, Divyanshu Dubey, Eoin P Flanagan, Sebastian Lopez-Chiriboga, Max R Trenerry, Nicholas L Zalewski, Anastasia Zekeridou, and Andrew McKeon. Brain dysfunction and thyroid antibodies: autoimmune diagnosis and misdiagnosis. Brain Communications, Jan 2021. URL: https://doi.org/10.1093/braincomms/fcaa233, doi:10.1093/braincomms/fcaa233. This article has 59 citations and is from a peer-reviewed journal.

Artifacts

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Hashimoto Encephalopathy (HE/SREAT): Comprehensive Disease Characterization Report

Summary

Hashimoto Encephalopathy (HE), also known as Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis (SREAT), is a rare, heterogeneous autoimmune encephalopathy defined by the presence of elevated antithyroid antibodies (anti-TPO and/or anti-TG), neuropsychiatric symptoms, and characteristic responsiveness to immunosuppressive therapy. First described by Brain et al. in 1966, HE remains one of the most clinically contested entities in neuroimmunology. Its diagnostic validity is challenged by findings that anti-TPO antibody prevalence in suspected HE patients (~8.1%) is nearly identical to that in healthy controls (~8.2%), and complete steroid response occurs in only ~32% of cases (PMID: 31882532). Despite these controversies, HE represents a clinically important diagnosis of exclusion because it identifies a subset of patients with severe, potentially reversible encephalopathy who respond to immunotherapy.

The clinical presentation is dominated by cognitive impairment (76.9%), seizures (46.1%), psychiatric symptoms including psychosis (38.5%), myoclonus (30.8%), and sleep disturbances (69.2%), occurring predominantly in females (F:M ratio ~4:1) who are typically euthyroid at presentation, with a bimodal age distribution peaking at 20-30 and 50-70 years (PMID: 19363998; PMID: 26167010). The pathophysiology remains incompletely understood, with four competing mechanistic hypotheses (autoimmune vasculitis, anti-neuronal antibodies, T-cell mediated immunity, and blood-brain barrier dysfunction). A landmark 2026 mouse model study identified HMGB1 as a key molecular mediator translating peripheral thyroid autoimmunity into central neuroinflammation via microglial activation and neurotoxic A1 astrocyte polarization (PMID: 41782877). Treatment follows a stepwise immunotherapy algorithm -- IV methylprednisolone as first-line (~61% effectiveness, ~32% relapse), followed by IVIG, plasmapheresis, rituximab, and novel FcRn antagonists for refractory cases -- with the majority of patients achieving at least partial recovery.

This report synthesizes evidence from 105 published papers and 13 confirmed findings across all 15 disease characterization domains, providing ontology-annotated entries suitable for knowledge base population.

1. Disease Information

Overview

Hashimoto Encephalopathy is a rare autoimmune encephalopathy associated with Hashimoto's thyroiditis, characterized by acute or subacute neuropsychiatric symptoms in the context of elevated antithyroid antibodies. The condition was first described in 1966 and has since been recognized as a treatable cause of encephalopathy, though its nosological status remains debated.

Key Identifiers

Synonyms and Alternative Names

• Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis (SREAT)
• Encephalopathy Associated with Autoimmune Thyroid Disease (EAATD)
• Nonvasculitic Autoimmune Inflammatory Meningoencephalitis (NAIM)
• Autoimmune Thyroid-Associated Encephalopathy

Data Sources

Information is derived primarily from aggregated disease-level resources including case series, systematic reviews, and retrospective cohort studies. The largest case series comprises 84 patients from multiple institutions across Japan and other countries (PMID: 19363998). Individual patient data come from case reports, small retrospective cohorts, and a 2024 systematic review analyzing treatment outcomes (PMID: 39000209).

2. Etiology

Disease Causal Factors

The precise etiology of HE remains unknown. The condition is fundamentally autoimmune in nature, arising in the context of Hashimoto's thyroiditis, but the specific mechanism by which thyroid autoimmunity produces central nervous system (CNS) dysfunction is debated. As stated by Manocchio et al. (2025): "While elevated TPO antibodies are frequently observed, a direct causal relationship with HE is unlikely, and their presence may indicate a general state of autoimmunity" (PMID: 40149702).

Genetic Risk Factors

No HE-specific causal genes have been identified. HE shares genetic susceptibility with autoimmune thyroid disease (AITD), which has approximately 70% heritability from twin studies. Key susceptibility genes include:

Lee et al. (2015) summarized: "AITD susceptibility genes can be categorized as either thyroid specific (Tg, TSHR) or immune-modulating (FOXP3, CD25, CD40, CTLA-4, HLA), with HLA-DR3 carrying the highest risk" (PMID: 26235382).

Environmental Risk Factors

• Iodine excess: Regions with higher iodine status show different DNA methylation patterns in AITD genes (ITGA6, PRKAA2, DAPK1) (PMID: 36420742)
• Selenium deficiency: Low selenium levels may increase AITD risk (data inconclusive)
• Vitamin D deficiency: Potential risk factor (data inconclusive) (PMID: 24609834)
• Infections: May trigger disease via molecular mimicry (PMID: 21234711)
• Smoking: Paradoxically diminished risk for Hashimoto's thyroiditis (PMID: 24609834)
• Female sex: Strongest demographic risk factor (F:M ratio 4:1 to 5:1), partially explained by fetal microchimerism and X-chromosome inactivation (PMID: 24609834)

Gene-Environment Interactions

Tomer et al. (2011) established the mechanistic framework: "These genes interact with environmental factors, such as infection, likely through epigenetic mechanisms to trigger disease" (PMID: 21234711). Epigenetic modifications include DNA methylation changes in immunoregulatory genes (TNF, IFNG, IL2RA, IL6, ICAM1, PTPN22, NOTCH1, HLA-DRB1) and non-coding RNA dysregulation (IFNG-AS1) (PMID: 36420742; PMID: 32916160).

Protective Factors

• Glutamine at HLA-DRbeta1 position 74: Protective against AITD (vs. arginine which confers risk) (PMID: 22735372)
• Moderate alcohol intake: Decreases risk of overt Hashimoto's hypothyroidism (PMID: 24609834)

3. Phenotypes

Clinical Phenotype Spectrum

The following table summarizes the major clinical phenotypes of HE with frequencies, HPO terms, and quality of life impact:

Sources: PMID: 26167010: "Clinical manifestations were cognitive impairment and behavioral changes in 10 (76.9%), sleep disturbance in 9 (69.2%), seizures in 6 (46.1%), headache in 4 (30.8%), psychosis or paranoia in 5 (38.5%), transient symptoms in 6 (46.1%), myoclonus in 4 (30.8%), ataxia or gait disorder in 4 (30.8%)"

Clinical Subtypes

Mattozzi et al. (2020) identified four distinct clinical syndromes (PMID: 31882532): 1. Psychiatric type (29%): Dominated by behavioral and psychiatric manifestations 2. Encephalopathy type (29%): Diffuse cognitive dysfunction and altered consciousness 3. NORSE-like type (25%): New-onset refractory status epilepticus pattern 4. Limbic encephalitis type (17%): Memory impairment and temporal lobe features

Additionally, an ataxia-predominant form has been described with cerebellar dysfunction as the main manifestation (PMID: 36081870), and rare presentations include orthostatic myoclonic jerks (PMID: 35946002), tic disorders (PMID: 24633901), and prominent bilateral tremor (PMID: 27790384).

Nonconvulsive Status Epilepticus

A Korean study of 22 patients found that nonconvulsive status epilepticus (NCSE) on EEG was observed in 6 patients, all of whom were intractable to antiepileptic drugs but responded to immunosuppressants (PMID: 38861245).

4. Genetic/Molecular Information

Causal Genes

No HE-specific causal genes have been identified. HE is not a Mendelian disorder; it follows a polygenic, multifactorial susceptibility model shared with AITD. The inheritance pattern is best described as multifactorial/polygenic with environmental modifiers.

Key Molecular Targets

• ENO1 (alpha-enolase) -- Gene ID: 2023; HGNC: 3350 -- Encodes the NH2-terminal alpha-enolase, target of anti-NAE autoantibodies found in 44% of HE patients. Anti-NAE antibodies show 91% specificity and 50% sensitivity for HE (PMID: 23777101). However, a 2024 systematic review noted that "the proposed anti NH2-terminal-alpha-enolase (anti-NAE) is non-specific for HE" (PMID: 39000209).
• TPO (thyroid peroxidase) -- Gene ID: 7173 -- Target of anti-TPO antibodies, the hallmark serological marker
• TG (thyroglobulin) -- Gene ID: 7038 -- Target of anti-TG antibodies
• HMGB1 (High Mobility Group Box 1) -- Gene ID: 3146 -- Identified as key mediator translating peripheral thyroid autoimmunity into CNS neuroinflammation (PMID: 41782877)

Epigenetic Information

DNA methylation patterns in AITD candidate genes (ITGA6, PRKAA2, DAPK1) differ between patients from regions with different iodine status, "providing a potential mechanism for associations between iodine and AITD" (PMID: 36420742). Non-coding RNA dysregulation, including lncRNA IFNG-AS1, modulates humoral and cellular immune responses in AITD (PMID: 32916160).

5. Environmental Information

Environmental Factors

• Iodine: Excess iodine intake is epidemiologically linked to increased AITD prevalence and alters epigenetic regulation of AITD genes (PMID: 36420742)
• Selenium: Deficiency may promote thyroid autoimmunity; supplementation studies show mixed results (PMID: 24609834)
• Vitamin D: Deficiency reported in AITD patients, but causality unestablished

Lifestyle Factors

Wiersinga (2014) reported: "Moderate alcohol intake decreases the risk on overt GH and overt Hashimoto's hypothyroidism. Current smokers - as well known - are at increased risk for Graves' disease, but - surprisingly - at diminished risk for Hashimoto's thyroiditis" (PMID: 24609834).

Infectious Agents

Infections are postulated to trigger AITD through molecular mimicry, but no specific pathogen has been definitively linked to HE. The gene-environment interaction operates through epigenetic mechanisms (PMID: 21234711).

6. Mechanism / Pathophysiology

Four Competing Mechanistic Hypotheses

The pathogenesis of HE involves four interrelated but distinct hypotheses:

UPSTREAM TRIGGER
      |
      v
Hashimoto's Thyroiditis (genetic susceptibility + environmental triggers)
      |
      v
Systemic Immune Dysregulation (thyroid autoantibodies, T-cell activation)
      |
      +---> Hypothesis 1: AUTOIMMUNE CEREBRAL VASCULITIS
      |     - Perivascular lymphocytic infiltration
      |     - Cerebral hypoperfusion on SPECT
      |     GO: GO:0006954 (inflammatory response)
      |
      +---> Hypothesis 2: ANTI-NEURONAL ANTIBODIES
      |     - Anti-NAE antibodies (44% of cases, 91% specificity)
      |     - Target: alpha-enolase on neuronal surfaces
      |     GO: GO:0002460 (adaptive immune response)
      |
      +---> Hypothesis 3: T-CELL MEDIATED AUTOIMMUNITY
      |     - Brain biopsies: T-cell dominant infiltration
      |     - CD4+ T cells infiltrate brain parenchyma
      |     CL: CL:0000624 (CD4-positive, alpha-beta T cell)
      |
      +---> Hypothesis 4: BBB DYSFUNCTION + HMGB1 (MOST RECENT)
    - CSF protein elevation (88.8%)
    - CSF anti-TPO presence
    - CSF IL-6 elevation
    - HMGB1 cytoplasmic translocation
    GO: GO:0045087 (innate immune response)
      |
      v
DOWNSTREAM EFFECTS
- Microglial activation (CL:0000129)
- A1-type neurotoxic astrocyte polarization (CL:0000127)
- Disrupted AQP4 polarization
- Neuronal dysfunction --> cognitive/psychiatric/seizure symptoms

The HMGB1 Breakthrough (2026)

Wang et al. (2026) provided the most mechanistically complete model to date using C57BL/6 mice with experimental autoimmune thyroiditis (EAT). Key findings include:

• "Mice with EAT, despite preserved systemic thyroid hormone levels, displayed significant deficits in both spatial and recognition memory" (PMID: 41782877)
• Pronounced microglial activation in cortex and hippocampus
• Increased A1-like neurotoxic astrocytes
• Disrupted AQP4 (aquaporin-4) polarization
• Infiltrating CD4+ T cells in brain parenchyma
• "Our results identify Hmgb1 as a key factor that translates peripheral thyroid autoimmunity into central neuroinflammation. It functions as a driving force behind pathogenic glial" activation (PMID: 41782877)

Molecular Pathways

• NF-kappaB pathway: HMGB1 activates NF-kappaB signaling in microglia and astrocytes (GO: GO:0007249)
• TLR4/RAGE signaling: HMGB1 binds TLR4 and RAGE receptors to initiate neuroinflammation
• Complement cascade: Potential role in vasculitic-type HE
• Cytokine signaling: CSF IL-6 elevation documented (PMID: 38085696)

Immune System Involvement

Relevant GO Terms

• GO:0006954 -- Inflammatory response
• GO:0006955 -- Immune response
• GO:0045087 -- Innate immune response
• GO:0002460 -- Adaptive immune response
• GO:0050776 -- Regulation of immune response
• GO:0019882 -- Antigen processing and presentation

7. Anatomical Structures Affected

Organ Level

Brain Regions

• Cerebral cortex (UBERON:0000956): Diffuse cortical dysfunction
• Hippocampus (UBERON:0002421): Memory impairment; microglial activation in mouse model
• Cerebellum (UBERON:0002037): Ataxia-predominant forms
• Temporal lobe (UBERON:0001871): Most frequent focal abnormality on MRI
• Basal ganglia/thalamus (UBERON:0002420 / UBERON:0004703): Movement disorders
• White matter (UBERON:0002316): T2/FLAIR hyperintensities

Cell Types Affected

• Neurons (CL:0000540): Primary target of immune attack
• Microglia (CL:0000129): Activated in neuroinflammation
• Astrocytes (CL:0000127): A1 neurotoxic polarization
• CD4+ T lymphocytes (CL:0000624): Brain-infiltrating effectors
• Thyroid follicular cells (CL:0002257): Primary autoimmune target
• Cerebral vascular endothelium (CL:0002543): BBB dysfunction

Lateralization

Brain involvement is typically bilateral and diffuse, though focal presentations occur. MRI lesions when present are often asymmetric. Anti-NAE-positive patients may show fluctuating white matter lesions (PMID: 31525528).

8. Temporal Development

Onset

• Age distribution: Bimodal, with peaks at 20-30 years and 50-70 years (PMID: 19363998). Range: 8 to 87+ years. Median onset ~48.5 years in some cohorts (PMID: 26167010).
• Onset pattern: Typically acute or subacute (days to weeks)
• Thyroid status at onset: Most patients are euthyroid; only 20% had prior history of Hashimoto's thyroiditis (PMID: 19363998)

Disease Course

Two main clinical course patterns: 1. Acute/relapsing vasculitic type: Stroke-like episodes, seizures, focal neurological deficits; episodic with remissions and relapses 2. Diffuse progressive type: Insidious cognitive decline resembling dementia, altered consciousness, psychosis; progressive course

Prognosis

• Glucocorticoid effectiveness: 60.94% (PMID: 39000209)
• Relapse rate: 31.67% following treatment (PMID: 39000209)
• Older adults (65+): 56.8% return to near-baseline; 29.4% partial improvement (PMID: 40323355)
• Overall with immunosuppressants: 90.5% (19/21) showed good outcomes (PMID: 38861245)
• Complete steroid response: Only 31.6% (6/19) (PMID: 31882532)
• Mortality: Generally considered non-fatal with appropriate treatment, though data are limited

9. Inheritance and Population

Epidemiology

• Prevalence: Estimated 2.1 per 100,000 (based on extrapolation from Hashimoto's thyroiditis prevalence and estimated HE occurrence rate)
• Incidence: Not precisely established; very rare
• Sex ratio: Female predominance, F:M ratio approximately 4:1 to 5:1; in the 84-patient Japanese series, 58 women and 26 men (F:M ~2.2:1) (PMID: 19363998)

Genetic Architecture

• Inheritance pattern: Multifactorial/polygenic (not Mendelian)
• Heritability: ~70% for underlying AITD (twin studies)
• Penetrance: Very low -- millions have AITD but only a tiny fraction develop HE
• Expressivity: Highly variable (psychiatric, encephalopathic, NORSE-like, limbic)

Population Demographics

• Geographic distribution: Reported worldwide; largest case series from Japan and Europe
• Ethnic predisposition: No clear ethnic predilection, though AITD prevalence varies by population
• Age distribution: Bimodal (20-30 and 50-70 years); can occur from childhood to elderly

10. Diagnostics

Diagnostic Criteria

HE remains a diagnosis of exclusion. The most rigorous proposed criteria (Mattozzi et al. 2020) require:

1. Subacute cognitive impairment, psychiatric symptoms, or seizures
2. Euthyroid or mild hypothyroidism
3. Serum TPOAb >200 IU/mL
4. Absent neuronal surface antibodies
5. No other identifiable etiologies

Critical limitation: The frequency of TPOAb in patients with possible autoimmune encephalitis without neuronal antibodies (8.1%) was similar to that of controls (8.2%), revealing poor diagnostic specificity (PMID: 31882532).

Laboratory Tests

Neuroimaging

• Brain MRI: Normal in 70-85% of cases. When abnormal: non-specific white matter T2/FLAIR hyperintensities (PMID: 36809420). In anti-NAE positive patients, "expanding and diminishing white matter lesions, emerging subcortical high-intensity spots on diffusion-weighted images, or reversible limbic lesions, which worsened at relapse and improved after recovery following immunotherapies" (PMID: 31525528).
• SPECT: Decreased cerebral blood flow (supports vasculitic hypothesis)
• FDG-PET: May show cortical hypometabolism

Electrophysiology

• EEG abnormalities: Present in 53.8-80% of cases
• Most common: generalized slowing
• NCSE observed in 6/22 patients in one series (PMID: 38861245)

Differential Diagnosis

Genetic Testing

Genetic testing is not applicable for HE diagnosis. HLA typing for AITD susceptibility is a research tool, not clinically indicated.

11. Outcome/Prognosis

Treatment Response and Outcomes

Prognostic Factors

• Early treatment initiation: Associated with better outcomes
• NCSE on EEG: Poor prognostic indicator; intractable to AEDs (PMID: 38861245)
• Age: Older patients may have slower recovery but still respond
• Anti-NAE positivity: Tends to be associated with acute encephalopathy pattern

Complications

• Residual cognitive deficits
• Persistent seizure disorder
• Steroid-related adverse effects (with prolonged therapy)
• Relapse upon steroid tapering

12. Treatment

Treatment Algorithm

FIRST-LINE: IV Methylprednisolone
  1g/day x 3-5 days (MAXO:0000750, CHEBI:6888)
  OR 500mg/day with similar outcomes
  --> Oral prednisolone taper
      |
      | If inadequate response or relapse
      v
SECOND-LINE OPTIONS:
  - IVIG 0.4g/kg/day x 5 days (MAXO:0000376)
  - Plasmapheresis (MAXO:0000127)
      |
      | If still refractory
      v
THIRD-LINE:
  - Rituximab (CHEBI:64357) - B-cell depletion
  - Azathioprine (CHEBI:2948)
  - Mycophenolate mofetil (CHEBI:168396)
      |
      | Novel/Emerging
      v
NOVEL THERAPIES:
  - Efgartigimod-alpha (FcRn antagonist) - rapid improvement
    in steroid-intolerant patients

Pharmacotherapy Details

First-line -- Corticosteroids (MAXO:0000750): - IV methylprednisolone 1g/day for minimum 3 days: used in 37.2% of older patients - Reduced dose 500mg/day (9.8%) with similar outcomes - "Majority of older patients (n = 48, 94.1%) were initially treated with steroids... Response is favorable, with 56.8% (n = 29) returning to near baseline functional status, while 29.4% (n = 15) showed partial improvement" (PMID: 40323355)

Second-line -- IVIG (MAXO:0000376): - "In the majority of the selected case-reports, IVIG was associated with a good outcome, sometimes even with dramatic improvements" (PMID: 37745658)

Novel -- FcRn antagonist (efgartigimod-alpha): - 800mg dose in an 83-year-old steroid-intolerant patient with recurrent HE - First report of this therapeutic class for HE (PMID: 41731401)

Supportive Care

• Antiepileptic drugs (MAXO:0000756): For seizure management (note: NCSE may be refractory to AEDs)
• Levothyroxine (CHEBI:18332, MAXO:0000779): For hypothyroidism when present
• Rehabilitation (MAXO:0000011): Cognitive re-education, physical therapy, psychosocial support -- "Evidence regarding rehabilitation for people affected by HE is limited, but neurorehabilitation strategies adapted from other neurological conditions... may be beneficial" (PMID: 40149702)

13. Prevention

Primary Prevention

No established primary prevention exists for HE. General strategies to reduce AITD risk include: - Adequate but not excessive iodine intake - Selenium supplementation (evidence inconclusive) - Vitamin D sufficiency maintenance - Avoidance of environmental triggers in genetically susceptible individuals

Secondary Prevention (Early Detection)

• Screening for anti-TPO/anti-TG antibodies in patients with unexplained encephalopathy
• Low threshold for HE evaluation in patients with known Hashimoto's thyroiditis presenting with neuropsychiatric symptoms
• EEG and MRI in patients with AITD and cognitive decline

Tertiary Prevention

• Maintenance immunosuppression to prevent relapse (31.67% relapse rate)
• Long-term steroid taper monitoring
• Regular neurological follow-up
• Seizure prophylaxis when indicated

Genetic Counseling

Not typically indicated for HE specifically, though family members may be screened for AITD given the strong heritability (~70%).

14. Other Species / Natural Disease

Animal Models of Thyroid Autoimmunity

OS Chicken Model

The OS chicken is the classic animal model for Hashimoto's thyroiditis. IL-15 was identified as constitutively upregulated: "Only IL-15 was up-regulated at all time points. IL-15 was also shown to be up-regulated in spleens of OS birds at embryonic day 20 and 5 days posthatch" (PMID: 11937583). Genetic analysis suggests SAT is regulated by a maximum of 3 genes (PMID: 11862410).

Comparative Biology

No animal model fully recapitulates the complete HE phenotype (thyroid autoimmunity + CNS dysfunction + steroid responsiveness). The EAT mouse model comes closest by demonstrating that thyroid autoimmunity alone -- in a euthyroid state -- can produce cognitive deficits and neuroinflammation.

15. Model Organisms

Available Models

1. OS Chicken (Gallus gallus) - Type: Spontaneous, avian - Phenotype recapitulation: Excellent for Hashimoto's thyroiditis (lymphocytic thyroid infiltration, autoantibodies, hypothyroidism) - CNS phenotype: None documented - Genetic regulation: Maximum 3 genes; one recessive gene for thyroid susceptibility, 1-2 dominant genes for immune abnormality - Resources: Available through specialized poultry genetics laboratories

2. C57BL/6 EAT Mouse (Mus musculus) - Type: Induced (porcine thyroglobulin injection + CFA) - Phenotype recapitulation: Best available model for HE -- cognitive deficits in spatial and recognition memory despite euthyroid state - Key features: Microglial activation, A1 astrocyte polarization, disrupted AQP4, HMGB1 translocation, CD4+ T cell brain infiltration - Limitations: Induced rather than spontaneous; single genetic background; acute model - Resources: Standard laboratory mouse; induction protocol described in PMID: 41782877

3. Canine Lymphocytic Thyroiditis - Type: Naturally occurring - Breeds affected: Multiple (Beagle, Doberman Pinscher, Golden Retriever, others) - Phenotype: Thyroid autoimmunity without encephalopathy - Relevance: Comparative pathology of thyroid autoimmunity only

Evidence Base

Key Publications Supporting This Report

Limitations and Knowledge Gaps

1. Diagnostic uncertainty: HE remains a diagnosis of exclusion with no pathognomonic biomarker. Anti-TPO antibodies lack specificity, and anti-NAE antibodies are present in fewer than half of cases with contested specificity.

2. No randomized controlled trials: All treatment evidence derives from case reports, case series, and retrospective studies. No RCTs exist for any HE therapy.

3. Pathogenic mechanism unknown: While four hypotheses exist and the HMGB1 mouse model is promising, the exact mechanism by which thyroid autoimmunity causes CNS dysfunction in humans remains unresolved. The mouse model findings await human validation.

4. Heterogeneity: The four clinical subtypes may represent distinct diseases grouped together by the presence of thyroid antibodies, which may be an epiphenomenon rather than a disease marker.

5. Epidemiological data: Prevalence and incidence figures are estimates. No population-based epidemiological studies exist for HE.

6. Long-term outcomes: Limited longitudinal data on cognitive recovery, relapse patterns, and quality of life over years.

7. Pediatric HE: Very limited data in children; most studies focus on adults.

8. No HE-specific genetic studies: All genetic data are extrapolated from AITD studies. No GWAS or exome studies have been performed specifically for HE.

9. Animal model limitations: No single model recapitulates the full HE triad (thyroid autoimmunity + CNS dysfunction + steroid responsiveness).

Proposed Follow-up Experiments/Actions

High Priority

1. Human validation of HMGB1: Measure CSF HMGB1 levels in HE patients vs. Hashimoto's thyroiditis patients without encephalopathy vs. healthy controls to validate the mouse model finding.

2. Prospective diagnostic cohort study: Evaluate a panel of biomarkers (anti-NAE, CSF IL-6, HMGB1, anti-TPO, CSF protein) in a prospective cohort of patients with suspected autoimmune encephalitis to derive an evidence-based diagnostic algorithm.

3. Randomized controlled trial of immunotherapy: Compare steroid monotherapy vs. steroid + IVIG vs. early rituximab in newly diagnosed HE using validated outcome measures (CASE score, mRS).

Medium Priority

1. Single-cell RNA-seq of brain biopsy/autopsy tissue: Characterize the cellular landscape of HE-affected brain tissue to identify the dominant immune cell populations and their activation states.

2. GWAS of HE patients: Perform genome-wide association study in HE (distinct from general AITD) to identify HE-specific susceptibility loci that may distinguish HE from uncomplicated Hashimoto's thyroiditis.

3. HMGB1 inhibitor therapeutic trial: Based on the mouse model, test HMGB1 inhibitors (e.g., glycyrrhizin, anti-HMGB1 antibodies) as targeted therapy in HE.

4. Longitudinal neuroimaging study: Track brain structural and functional changes (MRI, PET, SPECT) before and after treatment to identify imaging biomarkers of treatment response.

Lower Priority

1. EAT mouse model refinement: Develop a chronic/relapsing EAT model that better recapitulates the relapsing-remitting course of HE, including steroid responsiveness testing.

2. International HE registry: Establish a multicenter registry to collect standardized clinical, serological, imaging, and outcome data from HE patients worldwide.

3. Quality of life study: Administer validated QoL instruments (EQ-5D, SF-36) to HE patients at diagnosis and during follow-up to quantify the disease burden and recovery trajectory.

Ontology Term Summary

Disease Ontology

• MONDO:0015537 -- Hashimoto encephalopathy

Phenotype Terms (HPO)

• HP:0100543 -- Cognitive impairment
• HP:0001250 -- Seizures
• HP:0000709 -- Psychosis
• HP:0001336 -- Myoclonus
• HP:0001251 -- Cerebellar ataxia
• HP:0002360 -- Sleep disturbance
• HP:0002315 -- Headache
• HP:0001337 -- Tremor
• HP:0007185 -- Loss of consciousness
• HP:0002922 -- Increased CSF protein
• HP:0002353 -- EEG abnormality

Cell Types (CL)

• CL:0000540 -- Neuron
• CL:0000129 -- Microglial cell
• CL:0000127 -- Astrocyte
• CL:0000624 -- CD4-positive, alpha-beta T cell
• CL:0002257 -- Thyroid follicular cell

Anatomical Structures (UBERON)

• UBERON:0000955 -- Brain
• UBERON:0002421 -- Hippocampus
• UBERON:0000956 -- Cerebral cortex
• UBERON:0002037 -- Cerebellum
• UBERON:0002046 -- Thyroid gland
• UBERON:0002316 -- White matter

Biological Processes (GO)

• GO:0006954 -- Inflammatory response
• GO:0006955 -- Immune response
• GO:0045087 -- Innate immune response
• GO:0019882 -- Antigen processing and presentation

Chemical Entities (CHEBI)

• CHEBI:6888 -- Methylprednisolone
• CHEBI:64357 -- Rituximab
• CHEBI:2948 -- Azathioprine
• CHEBI:18332 -- Levothyroxine

Medical Actions (MAXO)

• MAXO:0000750 -- Corticosteroid therapy
• MAXO:0000376 -- Intravenous immunoglobulin therapy
• MAXO:0000127 -- Plasmapheresis
• MAXO:0000756 -- Antiepileptic drug therapy
• MAXO:0000779 -- Thyroid hormone replacement
• MAXO:0000011 -- Rehabilitation therapy

Report generated from systematic investigation across 5 iterations, reviewing 105 papers and confirming 13 findings. Disease characterization spans all 15 required sections with full ontology mapping and 22+ cited publications.