SUCCESSFUL EARLY TREATMENT OF ANTI-N-METHYL-D-ASPARTATE RECEPTOR ENCEPHALITIS ASSOCIATED WITH SMALL CELL LUNG CANCER IN AN ELDERLY MALE PATIENT: A CASE REPORT

Background

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, a type of autoimmune encephalitis, is characterized by acute onset neuropsychiatric symptoms, predominantly affects young females and is often associated with ovarian teratomas. While small cell lung cancer (SCLC) is a known cause of paraneoplastic encephalitis, its association with anti-NMDAR encephalitis is rare and often carries a poor prognosis because of limited response to immunotherapy. Case presentation: An 80-year-old male with no psychiatric history presented with flu-like symptoms and subsequently developed acute-onset neuropsychiatric symptoms, including pressured speech, agitation, memory impairment, and abnormal behavior. Autoimmune encephalitis was suspected due to a mildly elevated cerebrospinal fluid (CSF) white cell count and a mass in the right upper lung detected by whole-body computed tomography (CT) on Day 1 of hospitalization. High-dose intravenous corticosteroids were administered on Day 1, with prompt and sustained improvement in symptoms. CSF was subsequently confirmed positive for anti-NMDAR antibodies, and bronchoscopy-guided biopsy of the pulmonary mass confirmed SCLC. The patient recovered without neurological deficits and was discharged in stable condition on hospital Day 30.

Conclusion

We report a rare case of anti-NMDAR encephalitis associated with SCLC in an elderly male patient. Diagnosis in elderly individuals is often challenging because of atypical presentations and lower tumor association. Nonetheless, timely initiation of intervention may lead to favorable outcomes. Clinicians should consider autoimmune encephalitis, including antiNMDAR encephalitis, when evaluating acute-onset neuropsychiatric symptoms in elderly individuals, and should initiate early immunotherapy alongside tumor screening.