Successful treatment of acute autoimmune limbic encephalitis with negative VGKC and NMDAR antibodies: a case report

OBJECTIVE: To describe a case of acute nonherpetic limbic encephalitis (LE) with negative testing for antibodies directed against onconeuronal and cell membrane antigens, including voltage-gated potassium channels and N-methyl-D-aspartate receptor, that showed a dramatic response to immune therapy.\r\n\r\nMATERIALS AND METHODS: A 30-year-old woman manifested generalized seizures, altered consciousness, and memory impairment shortly after a prodromal viral illness. Few days later the patient developed a drug-resistant epileptic status.\r\n\r\nRESULTS: Electroencephalograph showed bitemporal slowing and paroxysmal slow wave bursts. Brain magnetic resonance imaging showed bilateral swelling in the medial temporal lobes. Cerebrospinal fluid analysis ruled out viral etiologies. A diagnostic search for cancer, including serum testing for known onconeuronal antibodies proved negative. Screening for cell membrane antigen antibodies, including voltage-gated potassium channels and N-methyl-D-aspartate receptor, was also negative. Suspecting an autoimmune etiology, we started an immunomodulatory treatment with intravenous immunoglobulin followed by a short course of oral prednisone, obtaining a full clinical recovery.\r\n\r\nCONCLUSIONS: Our report confirms previous observations of "seronegative" autoimmune LE, suggesting the presence of other, still unknown central nervous system antigens representing a target of a postinfectious, autoimmune response in these patients. Moreover, it emphasizes the importance of early recognition and treatment of acute autoimmune LE, to reduce the risk of intensive care unit-related complications and the occurrence of permanent cognitive or behavioral defects.