Speakers - 2026

Title: Hashimoto Encephalopathy Masquerading as Acute Psychosis with Concomitant SIADH: A Case Report of Dramatic Steroid Responsiveness

Abstract

Hashimoto Encephalopathy (HE), also known as Steroid-Responsive Encephalopathy Associated with Thyroiditis (SREAT), is a rare and frequently underdiagnosed autoimmune neurological condition. It presents with a wide clinical spectrum including altered sensorium, acute psychosis, seizures, and cognitive decline. Its co-occurrence with Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) makes clinical diagnosis particularly challenging, especially in elderly patients where multiple competing diagnoses exist simultaneously.

We report a 71-year-old male who presented to the emergency department with a 2-day history of altered sensorium, irrelevant speech, vomiting, and low-grade fever. On examination, GCS was E2V1M5 with drowsiness and bilaterally dilated pupils. Laboratory workup revealed significant hyponatremia. The patient was treated with 3% NaCl with initial partial improvement and was discharged. However, he was re-admitted with recurrent confusion and delirium, raising suspicion beyond a purely metabolic aetiology. Further investigations including thyroid antibody profile and PET-CT were performed. Thyroid antibody workup confirmed Hashimoto Encephalopathy. The hyponatremia pattern was consistent with SIADH, a recognised though rare association with HE. A course of high-dose corticosteroid therapy produced rapid and dramatic neurological recovery. The patient was discharged in hemodynamically stable condition with no relapse on follow-up.

This case draws attention to the diagnostic complexity of HE when presenting atypically alongside SIADH in an elderly male. It reinforces that steroid responsiveness remains both a diagnostic hallmark and the primary therapeutic strategy in HE. Prompt recognition prevents unnecessary investigations, prolonged hospitalisation, and significant morbidity.

What Will the Audience Take Away?

• Recognise Hashimoto Encephalopathy as a differential in elderly patients with unexplained acute psychosis and encephalopathy
• Understand the rare but documented association between HE and SIADH
• Learn the diagnostic criteria and workup required to confirm HE in clinical practice
• Appreciate steroid therapy as both a confirmatory diagnostic tool and definitive treatment