Anti-N-Methyl-D-Aspartate Receptor Encephalitis Associated With Small Cell Lung Cancer: A Case Report

Anti-N-methyl-d-aspartate receptor encephalitis (NMDARE) is an autoimmune disorder with a clinical presentation that overlaps with that of a myriad of neuropsychiatric conditions. Delays in diagnosis have been linked to long-term complications that affect a patient's quality of life. A 60-year-old female patient with a medical history of emphysema with chronic respiratory failure, hypertension, diabetes, morbid obesity, and hyperlipidemia presented to the hospital after she was found confused at home with limited verbal output, raising concerns for cerebrovascular events or toxic metabolic encephalitis. Neuroimaging and EEG results were unremarkable. The patient continued to experience respiratory distress that delayed diagnostic procedures. She was later diagnosed with small-cell lung cancer, and cerebrospinal fluid tests were positive for anti-N-methyl-d-aspartate receptor antibodies. Gradual improvement in cognitive function and speech was noted after treatment with immunotherapy. This case study underscores the importance of considering rare neurological conditions in patients with heightened cardiovascular risk profiles. Furthermore, it provides insights into the potential diagnostic and therapeutic challenges that can arise in the domain of anti-NMDARE in such patients.