Clinical and Immunological Investigations in Patients with Suspected Autoimmune Post-Herpes Simplex Encephalitis (745)

Objective: To report the clinical and immunological features of patients with suspected autoimmune post-herpes simplex encephalitis (Post-HSE). Background: Post-HSE is an autoimmune encephalitis triggered by HSE and occurs in 27% of patients with HSE. Post-HSE is associated with development of neuronal surface antibodies (NS-Abs); however, NS-Abs are not always identified in patients with suspected Post-HSE, and the cause of NS-Ab-negative cases remains unclear. Design/Methods: This study included 6 patients with suspected Post-HSE (median age, 58.5 years [33–68]; 4 [66.7%] male) who underwent testing for NS-Abs between January 1, 2016 and April 30, 2019. Post-HSE was suspected because neuro-psychiatric symptoms worsened or newly developed but no reactivation of herpes simplex virus type 1 (HSV-1) was confirmed in CSF. The clinical features were compared between patients with and without NS-Abs. Results: HSV-1 DNA was detected in CSF at onset of HSE but not at relapse. Median interval from HSE onset to relapse was 31 days (range, 9–78 days). Main relapsing symptoms included abulia/depression/slow thinking (n=4), followed by fever (n=2) and involuntary movements/decreased consciousness level (n=1). Median CSF WBCs at relapse were 15.5/mm3 (6–485). OCBs were detected in 5/5. NS-Abs were identified in 3 (50%); 2 NMDAR and 1 against unknown antigens. Compared with NS-Ab-negative patients, NS-Ab-positive patients had longer median interval (50 days vs 11 days) with clear convalescent period after HSE and lower median CSF pleocytosis at relapse (7/mm3 vs 128/mm3). In 5 of 6 patients initial lesions expanded at relapse. All patients received immunotherapy; 6 high-dose steroids, 3 immunoglobulins, 1 cyclophosphamide. Outcome was poor (defined as mRS≥3) in 4 (66.7%) patients at the last followed-up (median 10 months, range 6.3–26.9); the outcome was good in 2 (mRS≤2). Conclusions: NS-Abs were identified in 50% of patients with suspected Post-HSE. The pathophysiology of early worsening without NS-Abs production may be different from that of NS-Ab-positive Post-HSE. Disclosure: Dr. Kaneko has nothing to disclose. Dr. Iizuka has received research support from The Japan Epilepsy Research Foundation and Astellas Pharma Inc.Dr. Iwase has nothing to disclose. Dr. Nagai has nothing to disclose. Dr. Kaneko has nothing to disclose. Dr. Kitamura has nothing to disclose. Dr. Tomita has nothing to disclose. Dr. Igarashi has nothing to disclose. Dr. Irioka has nothing to disclose. Dr. Arai has nothing to disclose. Dr. Kanazawa has nothing to disclose. Dr. Nishiyama has received research support from Daiichi Sankyo Co., Ltd., Otsuka Pharmaceutical Company, Ltd., Dainippon Sumitomo Pharma, Co., Ltd., and Eisai Co., Ltd..