Anti-NMDAR encephalitis after resection of melanocytic nevi: report of two cases

BACKGROUND Encephalitis with antibodies against N-methyl D-aspartate receptor (NMDAR) is recognized as a group of antibody-mediated neuropsychiatric syndromes, which occurs with and without a tumor association. Neoplasm may contribute to the pathogenesis of Anti-NMDAR encephalitis in tumor-positive patients. However, the underlying causes in tumor-negative patients are largely unknown. This is the first report, of which we are aware, of two cases of anti-NMDAR encephalitis after the resection of melanocytic nevus. CASE PRESENTATION We describe 2 female patients in their 20s confirmed with anti-NMDAR encephalitis. They shared two points in common: About several weeks (2 weeks and 5 weeks respectively) before the initial symptom, both of them underwent a resection of melanocytic nevi; the screening tests for an ovarian teratoma and other tumors were all negative. A 25 year-old woman presented with seizure, psychiatric symptoms and behavioral change for 2 weeks. Electroencephalogram indicated electrographic seizures. Anti-NMDAR antibodies were all positive in the cerebrospinal fluid and serum. Her symptoms relieved gradually after the treatment with steroids and mycophenolate mofetil. Another patient admitted to our hospital with psychosis, behavioral change and complex partial seizure over a period of 5 months. Electroencephalogram demonstrated generalized slow activities. High titres of anti-NMDAR antibodies were both detected in the cerebrospinal fluid and serum. She responded well to the first-line immunotherapy and got substantial recovery. CONCLUSION Our cases provided an observational link between anti-NMDAR encephalitis and resection of nevi. We postulate that the exposure of certain antigen on nevus cell caused by nevi excision, which might be NMDA receptor or other mimic cross-reactive antigens, may trigger an autoimmune response resulting in encephalitis. This suggested a potential site of antigen exposure triggering the immune response in non-tumor associated anti-NMDAR encephalitis, which may lend support to elucidating the underlying immunopathological mechanisms. Further studies are expected for investigating the expression of NMDA receptor on nevus cell and evaluating the validity of this hypothesis.