Dual association of autoimmune encephalitis with anti-NMDAR and anti-GAD65 antibodies: A Case Report with Literature Review

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is the most common type of autoimmune encephalitis, whereas anti-glutamic acid decarboxylase 65 (antiGAD65) encephalitis is a rare autoimmune condition. The coexistence of these two conditions has been rarely reported. In this article, we will discuss this rare association through a case report and attempt to determine its main characteristics. We report the case of an 18-year-old male with no medical history, admitted to the medical Intensive Care Unit (ICU) with a decreased level of consciousness, bizarre behavior, and abnormal movements for one week. These symptoms followed the progression of initial signs such as delirium, which had begun two months earlier. Laboratory analysis revealed an inflammatory syndrome with rhabdomyolysis. Cerebral angio-MRI findings were unremarkable. The electroencephalogram (EEG) showed slow, non-reactive activity. Cerebrospinal fluid (CSF) analysis and infectious studies were normal. However, immunological testing using the immunofluorescence technique revealed the presence of anti-NMDAR antibodies in both serum and CSF, as well as anti-GAD65 antibodies in the serum. The positron emission tomography (PET) scan screening for neoplasm was negative. Therapeutically, the patient was treated with anticonvulsants, antipsychotics, intravenous immunoglobulins, corticosteroids, plasma exchanges, cyclophosphamide, and rituximab. Consequently, he demonstrated a remarkable gradual clinical improvement. This case highlights an aspect of autoimmune dysregulation that may lead to atypical and severe clinical presentations. The co-occurrence of anti-NMDAR and anti-GAD65 encephalitis is a rare condition that can lead to severe manifestations. Early diagnosis using a broad antibody panel facilitates timely and appropriate management.