To describe the first reported case of anti-NMDA receptor (NMDAR) encephalitis related to renal cell carcinoma (RCC).

Anti-NMDAR encephalitis is an autoimmune encephalitis characterized by a well-defined neuropsychiatric syndrome and CSF antibodies against the GluN1 subunit of the NMDAR. Forty percent of cases are related to underlying tumors, the vast majority ovarian teratomas (94%). Rarely, other tumors have been described, including lung, breast, and testicular carcinomas. We report a 20-year-old female with a typical clinical syndrome and confirmatory antibodies in the context of underlying RCC.

A 20-year-old female presented to the ED with behavioral changes, involuntary movements, tachycardia, and alternating obtundation with agitation, progressing over 3 weeks. Involuntary movements were severe and resulted in rhabdomyolysis. Sedation was required for control of movements, with subsequent endotracheal intubation. Brain MRI showed bilateral mesiotemporal T2/FLAIR hyperintensities. Anti-NMDAR antibodies were present in the serum (1:640) and CSF (1:320). Malignancy screening revealed renal mass concerning for RCC, which was confirmed upon resection. She was started on high dose IV methylprednisolone. Lack of response led to escalating immunotherapy with plasmapheresis, rituximab, and cyclophosphamide sequentially. Clinical course was complicated by prolonged ICU admission, prolonged sedation for involuntary movements, dysautonomia requiring temporary pacemaker and repeat infections. She began improving 2 months after initial treatment and was discharged to inpatient rehabilitation 100 days after admission, ambulatory with mild residual neuropsychiatric symptoms. Repeat malignancy screenings, including whole-body imaging and transvaginal U/S were negative for other malignancies.