353. HSV-Induced Anti-NMDAR Encephalitis

BACKGROUND: N-Methyl-d-aspartate receptor (NMDAR) is a glutamate receptor on nerve cells that controls synaptic plasticity and memory function. Anti-NMDAR encephalitis is a rare autoimmune disease causes by antibodies (Ab) against GluN1 subunit of the NMDAR. Preceding Herpes simplex virus-1 encephalitis (HSVE) is a well-recognized infectious trigger. First reported in female patients with ovarian teratoma, and more recently with germ cell tumors in males. METHODS: A 61-year-old male presented with agitation, behavioral changes, and confusion. Eight months prior, he was diagnosed with HSVE and treated with 21 days of intravenous acyclovir. Following therapy, he suffered from residual cognitive and personality changes with slow recovery until 3 months prior to admission encephalopathy again worsened. An extensive investigation was unrevealing except for a CSF lymphocytic pleocytosis, positive anti-NMDAR Ab titer 1:64 and imaging changes consistent with post-viral encephalitis. At that point, HSV-induced anti-NMDAR encephalitis was diagnosed. A PET scan did not show any occult malignancies. Two cycles of plasmapheresis were attempted over 4 months period with limited success in improving his worsening neurologic deficits. RESULTS: HSVE induced autoimmune encephalitis is a rare complication, primarily affecting children and young adults. Auto Ab develop 1–4 weeks after HSVE, manifesting as choreoathetosis and/or orofacial dyskinesia in children and psychiatric symptoms in young adults. CSF Ab titer is highly sensitive and specific. Proposed mechanisms include either viral reactivation or a post-infectious autoimmune process. Immunotherapy with tumor resection (if present) has been promising with less frequent need for second-line therapy in primary condition, compare with HSVE-induced condition where tumors have not been reported and resistance to first-line therapy has been observed. Progressive decline in neurologic function post HSVE prompted an evaluation for paraneoplastic conditions in our patient that ultimately revealed the diagnosis. The unique feature of this case is the age of the patient and preceding HSVE which triggered this autoimmune process. CONCLUSION: Physicians should consider anti-NMDAR encephalitis in the differentials for relapsing patients post HSVE. DISCLOSURES: All authors: No reported disclosures.