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I am 3rd year resident of internal medicine

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Give short note on hashimoto encephalopathy

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Hashimoto encephalopathy steroid responsive

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Here is a concise but complete note on Hashimoto Encephalopathy:

Hashimoto Encephalopathy (HE)

Also known as: Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis (SREAT)

Definition

A rare autoimmune encephalopathy associated with Hashimoto thyroiditis, characterized by high titers of antithyroid antibodies and dramatic response to corticosteroids. Importantly, most patients are euthyroid at onset - thyroid dysfunction is NOT required for diagnosis.

Epidemiology

  • More common in adolescent females and middle-aged women
  • Rare overall; exact prevalence uncertain
  • Familial clustering of other autoimmune diseases is common
  • Often misdiagnosed as Creutzfeldt-Jakob disease due to overlapping features

Pathogenesis

The exact mechanism is not fully established. Proposed theories:
  • Autoimmune cerebral vasculitis with immune complex deposition leading to cerebral hypoperfusion
  • Antithyroid antibodies (anti-TPO, anti-thyroglobulin) found in CSF, suggesting intrathecal production
  • Some overlap with paraneoplastic limbic encephalitis mechanisms

Clinical Features

Two main patterns:
  1. Relapsing-remitting - stroke-like episodes, confusion, focal deficits
  2. Slow progressive - cognitive decline with psychiatric features
Neurological:
  • Confusion / cognitive impairment (80%)
  • Myoclonus - hallmark feature; often the clue to diagnosis
  • Seizures, including generalized tonic-clonic and nonconvulsive status epilepticus
  • Tremor, ataxia, opsoclonus, chorea, dystonia
  • Hemiparesis, transient aphasia, stroke-like episodes
  • Myelopathy (rare)
Psychiatric:
  • Psychosis, hallucinations (predominantly visual), suicidal ideation (90-100%)
  • Agitation, restlessness, apathy, personality changes

Diagnostic Criteria (Clinical Triad)

  1. Neuropsychiatric symptoms as above
  2. Elevated antithyroid antibodies - anti-TPO (present in ~100%), anti-thyroglobulin (~70%)
  3. Exclusion of other causes (infection, metabolic, structural, toxic, prion disease)

Investigations

TestFindings
Serum anti-TPO / anti-TGElevated (key marker)
TSH / T3 / T4Usually normal; hypothyroidism in ~52%
CSFElevated protein (60%), mild pleocytosis in some; antibodies may be detectable
EEGDiffuse background slowing; can show epileptiform activity
MRI brainNormal in most; some show nonspecific T2 white matter hyperintensities (frontotemporal / subcortical)
MR SpectroscopyHypoperfusion evidence, mainly frontotemporal
Key point: Anti-TPO antibodies are detectable in many healthy older women and 2/3 of Graves' patients - so their presence alone is not diagnostic. Clinical context is essential.

Treatment

First-line: High-dose corticosteroids (e.g., IV methylprednisolone or oral prednisone with slow taper over weeks to months)
  • 90-98% respond to steroids
  • Full recovery in ~55% of cases
  • Does NOT respond to thyroxine replacement
For refractory or relapsing cases:
  • Azathioprine, mycophenolate mofetil, methotrexate, hydroxychloroquine, cyclophosphamide
  • Periodic IVIG
  • Plasma exchange (rapid response in severe/comatose cases)

Key Differential Diagnoses

  • Creutzfeldt-Jakob disease (subacute cognitive decline + myoclonus)
  • Autoimmune / paraneoplastic limbic encephalitis (anti-NMDAR, anti-LGI1, etc.)
  • CNS vasculitis
  • Viral encephalitis
  • Toxic-metabolic encephalopathy

Pearls for the Clinician

  • Think of HE when you see subacute encephalopathy + myoclonus - do not anchor on CJD without checking anti-TPO
  • The condition can occur even in euthyroid patients - do not rule it out based on normal TFTs
  • It is a diagnosis of exclusion but has a treatable cause - early recognition matters
  • Recent systematic review (Pempera et al., Int J Mol Sci, 2024 - PMID 39000209) highlights ongoing difficulties in standardizing diagnostic and treatment criteria
Sources: Adams & Victor's Principles of Neurology, 12th Ed., p.1159; Bradley & Daroff's Neurology in Clinical Practice, p.1253-1254
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