SUN-371 - Steroid-Responsive Encephalopathy Associated with Autoimmune Thyroiditis Presenting as Acute Psychosis

Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT), also known as Hashimoto encephalopathy, is a rare and potentially reversible autoimmune neurological disorder. It is characterized by subacute onset of encephalopathy and neuropsychiatric manifestations occurring in the presence of thyroid autoimmunity, most commonly elevated anti–thyroid peroxidase (TPO) or anti-thyroglobulin antibodies. Thyroid hormone levels are often normal or only mildly abnormal, making clinical recognition challenging. SREAT remains a diagnosis of exclusion, requiring thorough evaluation to rule out other etiologies.

The predominant features include cognitive impairment, altered levels of consciousness, seizures, myoclonus, and prominent psychiatric symptoms such as psychosis, hallucinations, mood disturbances, and behavioral changes, reason why is frequently misdiagnosed as a primary psychiatric disorder or other forms of encephalitis, leading to delays in therapy.

We report the case of a 59-year-old incarcerated woman with a history of depression, anxiety, and chronic alcohol use who presented with acute altered mental status, paranoia, visual hallucinations, and bizarre behavior. She was found disoriented, incoherent, and sitting in her own feces, prompting hospital transfer. On admission, she denied chest pain, gastrointestinal symptoms, palpitations, or dizziness. Vital signs were stable. Neurological examination revealed impaired attention, judgment, and memory, with intermittently incoherent speech and poor comprehension. Cranial nerves were intact, motor strength was preserved, and no focal neurological deficits were observed. Thyroid studies demonstrated elevated TSH (7.2 mIU/L, n 0.5 to 5.0 mIU/L) with initially discordant free T4 levels. Neuroimaging studies, including brain CT and MRI, along with EEG evaluation, showed no significant abnormalities.

An extensive diagnostic evaluation was negative, including HIV PCR, herpes simplex virus, cytomegalovirus, Epstein–Barr virus, JC virus, syphilis, and autoimmune encephalitis panels. Cerebrospinal fluid analysis revealed a noninflammatory profile with normal IgG index, absence of oligoclonal bands, and normal myelin basic protein. Thyroid antibody testing demonstrated markedly elevated thyroid peroxidase and thyroglobulin antibodies, consistent with autoimmune thyroiditis. Given the severity of symptoms and exclusion of alternative etiologies, SREAT was suspected and treated with high-dose intravenous methylprednisolone followed by a prednisone taper, resulting in rapid clinical improvement within twenty-four hours. Subclinical autoimmune hypothyroidism was managed with levothyroxine. This case highlights SREAT as a rare but reversible cause of acute psychosis and encephalopathy and emphasizes the need for clinician awareness of this treatable condition.

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