Seronegative Autoimmune Limbic Encephalitis: A Case Report.

Autoimmune encephalitis (AE) is an immune-mediated disorder of the central nervous system (CNS). Its definitive diagnosis relies on the identification of a specific antibody. Autoimmune limbic encephalitis (LE) is a subset of AE characterized by inflammation of the limbic cerebral cortex. Cognitive decline, behavioral disturbance, and seizures are its cardinal manifestations. We present the case of a 70-year-old man with subacute progressive gait imbalance, cognitive impairment, and psychiatric manifestations. Extensive serum and cerebrospinal fluid (CSF) investigations did not reveal any abnormality. Autoimmune and paraneoplastic encephalitis antibody panels were negative. Magnetic resonance imaging (MRI) and positron emission tomography (PET) brain scans suggested LE. He responded well to immunotherapy. This case illustrates that AE must be suspected in the appropriate setting, even in the absence of a specific antibody. These patients should be given the benefit of early immunotherapy.