Obsessive‐compulsive disorder as an initial manifestation of anti‐glutamic acid decarboxylase antibody‐associated encephalitis

We present the case of a 44‐year‐old woman with type 1 diabetes and anti‐glutamic acid decarboxylase antibody (GAD‐Ab) (6100 U/mL in serum), manifesting as a one‐month history of compulsive writing in her self‐monitoring blood glucose (SMBG) diary and a one‐week history of seizures before admission. On admission, she was diagnosed with GAD‐Ab‐associated encephalitis (GAD‐AE), and compulsive writing consistent with obsessive‐compulsive disorder (OCD) caused by a repetitive and persistent urge to neutralize anxiety manifesting as clearly excessive writing. Immunotherapy, including corticosteroids, azathioprine, and intravenous immunoglobulin, improved her compulsive writing, and seizures disappeared following lacosamide treatment. Two months after discharge, compulsive writing reappeared and the patient was successfully treated with temporary immunotherapy intensification. After a stable period of 2 years, the patient died due to hypoglycemic encephalopathy. Overall, we showed that GAD‐AE may cause OCD.