Steroid-Responsive Encephalopathy Associated With Autoimmune Thyroiditis Presenting As Acute Psychosis: A Diagnostic Pitfall

Steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT) is a rare autoimmune encephalopathy characterized by heterogeneous neuropsychiatric manifestations. We describe the case of a 59-year-old woman with a history of anxiety and severe alcohol use disorder who presented with acute psychosis, marked behavioral disorganization, and cognitive impairment initially attributed to alcohol withdrawal, metabolic disturbance, or primary psychiatric illness. Despite extensive evaluation, including negative infectious, toxicologic, metabolic, structural, and paraneoplastic workups, no clear etiology was identified. Additional findings, including a reactive HIV screening assay and elevated vitamin B12 levels, further complicated the diagnostic process. Thyroid studies revealed markedly elevated anti-thyroid peroxidase and anti-thyroglobulin antibodies with subclinical hypothyroidism, raising suspicion for SREAT. Following initiation of high-dose intravenous (IV) corticosteroids, the patient demonstrated rapid and marked improvement in mental status within 48 hours, supporting an immune-mediated process. Subsequent cerebrospinal fluid analysis, electroencephalography, and brain imaging remained unremarkable. This case highlights the diagnostic challenges of SREAT, particularly in patients with comorbid psychiatric and substance use disorders, and underscores the importance of considering autoimmune encephalopathy in cases of unexplained neuropsychiatric decline. Early recognition and timely immunosuppressive therapy may lead to significant clinical recovery and prevent prolonged morbidity.