Abstracts

Rationale: To investigate the association of anti-glutamic acid decarboxylase autoantibodies (GAD Ab) titer with neurological manifestations. Methods: A retrospective study was conducted for adult patients who underwent testing for the serum GAD Ab between April 1, 2016 and March 31, 2019 at tertiary emergency hospital. Association of GAD Ab titer with present or past history of coma and other clinical features were evaluated. High and low titer groups were defined as patients with GAD Ab>1000 IU/L and those with >5 IU/L and 1000 and less, respectively. Results: Of 445 patients, 70 patients were tested GAD Ab to assess the etiology of coma (age 67.5+-16.3 years; mean +- SD, 33 males Group 1). 9 out of 70 patients (12.9%) were positive for GAD Ab (7 with high, 2 with low titers). Of 375 patients without episodes of consciousness disturbance (age 63.6+-15.0 years, 214 males : Group 2), 18 patients were positive for GAD Abs (1 with high, 17 with low titers). Number of patients with GAD Ab positivity (9/70 vs 19/375, p=0.02, Fisher's exact test), high titer of GAD Ab(7/70 vs 1/375, p<0.00001), and the presence of tremor or myoclonus(22/70 vs 3/375, p<0.00001) were significantly more in Group 1 as compared to Group 2. High GAD Ab titer significantly associated with history of coma and showed a tendency of association with death outcome (3/8 vs 2/19, p=0.07). 3 patients with high titer in Group 1 were treated with immunosuppressant therapy (IV high-dose methylprednisolone 1,000 mg/day for 3 days to 3 patients, IV immunoglobulin 0.4 g/kg/day for 5 days to 2, and plasma exchange to 1) and the second-line immunotherapy (IVCPA 500 mg/m2 for 1 day) to 1, which were not effective. EEG of the 3 patients 2 patients showed generalized continuous rhythmic delta activity (GRDA) with frequency evolution, and frontal intermittent rhythmic delta activity in 1. The former 2 patients had death outcome. Conclusions: Autoimmune encephalopathy associated with GAD Ab is one of the important etiology that accounts for approximately 13% of present or past history of coma with poor prognosis. GRDA with frequency evolution can be a surrogate marker of poor prognosis in patients with high GAD Ab titer. Funding: No funding