Lethargy With Reversible Bilateral Basal Ganglia and Substantia Nigra Lesions in Anti-N-Methyl-D-Aspartate Receptor Encephalitis: A Case Report.

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a neuroinflammatory disorder characterized by a broad spectrum of neuropsychiatric symptoms, and the optimal treatment strategy for atypical or refractory cases has not been well established. We report the case of a 26-year-old woman with anti-NMDAR encephalitis associated with an ovarian teratoma who presented with acute psychiatric and neurological manifestations. The patient underwent tumor resection followed by first-line immunotherapies, including corticosteroids, intravenous immunoglobulin, and plasma exchange. Because of persistent neurological symptoms, second-line immunotherapy with cyclophosphamide was initiated, leading to gradual clinical improvement. However, she subsequently developed lethargy and upper-limb tremors, accompanied by bilateral basal ganglia and substantia nigra abnormalities on MRI. Notably, both her clinical symptoms and radiological abnormalities improved following an additional course of cyclophosphamide treatment. This report highlights a rare clinical and radiological manifestation and suggests that additional immunotherapy may be effective for delayed neurological worsening.