N-methyl-D-aspartate receptor autoimmune encephalitis presenting with opsoclonus-myoclonus: treatment response to plasmapheresis.

OBJECTIVES To report the clinical, laboratory, and radiographic features and the response to plasmapheresis in a patient with encephalopathy, opsoclonus, and myoclonus whose cerebrospinal fluid was positive for N-methyl-D-aspartate receptor-IgG. DESIGN Case report. SETTING St Marys Hospital, Rochester, Minnesota. PATIENT A 27-year-old woman with a history of episodic migraine developed subacute progressive myoclonus, opsoclonus, and encephalopathy. RESULTS Magnetic resonance imaging demonstrated nodular leptomeningeal enhancement in the superior cerebellar folia and subsequent T2 hyperintensities in the periventricular regions and amygdala. A positron emission tomographic scan of the head demonstrated predominantly frontotemporoparietal cortical hypometabolism with sparing of the primary sensory and motor cortices. Cerebrospinal fluid examination revealed a lymphocytic pleocytosis, mildly elevated protein level, elevated IgG index, and positive oligoclonal banding. Autoimmune cerebrospinal fluid screening revealed a neural-specific IgG that bound to synapse-rich regions of mouse hippocampus and cerebellar granular layer; the neural-specific IgG was confirmed to be N-methyl-D-aspartate receptor specific. No neoplasm was detected by physical examination or by whole-body computed tomography and positron emission tomography. A 5-day course of high-dose intravenous methylprednisolone sodium succinate yielded limited improvement, and the patient subsequently required intensive care unit admission following a pulseless electrical activity arrest associated with pulmonary embolism. The encephalopathy improved dramatically after plasmapheresis. CONCLUSIONS This case highlights opsoclonus and myoclonus as manifestations of autoimmune N-methyl-D-aspartate receptor encephalitis in the setting of a novel appearance on positron emission tomography, and it shows a remarkable clinical response to plasmapheresis.