Atypical Association of Autoimmune Limbic Encephalitis with Anti-NMDA Receptor Antibodies in a Young Male Patient: Clinical, Imaging, and Neuropsychological Characteristics

The spectrum of autoimmune encephalitis (AE) encompasses several entities characterized by a variable frequency of psychiatric symptoms, cognitive dysfunction, focal deficits, and seizures. Although patients with AE can be categorized in specific syndromes, overlapping manifestations are also common. Furthermore, atypical correlations between clinical phenotypes and autoantibody profiles could occur in rare cases. Here, we report the rare case of a young adult man attending due to new-onset seizures and a history of memory loss, autonomic disturbances, headache, behavioral changes, and visual and olfactory hallucinations. The patient was subjected to a complete diagnostic approach that included a comprehensive laboratory workup, neuropsychological testing, electroencephalogram, cerebrospinal fluid (CSF) analysis, brain MRI, and positron emission tomography/computed tomography scan that revealed a functional and structural compromise of the bilateral medial temporal lobes. Together with the clinical manifestations of the patient, these findings were compatible with the diagnosis of autoimmune limbic encephalitis (ALE). Strikingly, further analysis of the CSF showed autoantibodies against the N-methyl-D-aspartate (NMDA) receptor. We found very few cases of the co-occurrence of anti-NMDA receptor antibodies and nonparaneoplastic ALE in the literature, especially in male patients. Our report exemplifies the complicated differential diagnosis of ALE and adds clinical information of the association with anti-NMDA receptor antibodies.