Hashimoto's Encephalopathy with Use of Intravenous Immunoglobulin as First-Line Therapy.

Hashimoto's encephalopathy is an uncommon cause of altered mental status in hospitalized patients and is challenging to diagnose, particularly in the presence of other psychiatric comorbidities. Corticosteroids are the primary treatment. Here, we present a patient with history of post-traumatic stress disorder and prior substance abuse admitted with profound altered mental status and agitation requiring admission to the intensive care unit and mechanical ventilation. He was treated with intravenous immunoglobulin (IVIG) instead of the standard steroid course because of concerns for worsening agitation. The patient had improvement with IVIG infusions, returned to a functional state, and has remained on IVIG therapy monthly since the initial episode without any disease recurrence.