CNSC-34. Marginal Zone B-Cell Lymphoma Presenting With Recurrent Seizures and Leptomeningeal Enhancement: A Diagnostic Challenge

BACKGROUND Leptomeningeal involvement in low-grade lymphomas is rare and may mimic infectious or autoimmune encephalitis. We report a case of marginal zone B-cell lymphoma initially presenting with recurrent focal seizures and confusion, ultimately diagnosed through serial imaging and CSF analysis. METHODS A 60-year-old male presented in 2017 with transient right hemiparesis, dysarthria, and confusion. Brain MRI showed diffuse leptomeningeal enhancement. Serial EEGs revealed intermittent slow waves without epileptiform discharges. Despite antiseizure therapy, episodes persisted. CSF analyses in 2018 and 2019 consistently showed lymphocyte-predominant pleocytosis and elevated protein levels. Extensive infectious, autoimmune, and paraneoplastic panels were negative. Abdominal CT revealed retroperitoneal soft tissue encasing the aorta and ureters. Biopsy confirmed marginal zone B-cell lymphoma. RESULTS The patient was diagnosed with Stage II marginal zone lymphoma with presumed leptomeningeal involvement. Despite antiseizure medications and corticosteroids, neurological symptoms continued. Later complications included hyponatremia from oxcarbazepine, parasitic colitis (Strongyloides stercoralis), and septic shock. Immunosuppressive treatment and intrathecal methotrexate were initiated, but the patient deteriorated and died of septic shock in November 2019. CONCLUSIONS This case highlights the diagnostic complexity of indolent lymphoma with CNS involvement. Persistent leptomeningeal enhancement with seizure-like episodes should prompt evaluation for lymphomatous meningitis even in low-grade lymphoma. Early multidisciplinary assessment is critical for timely diagnosis and intervention. Opportunistic infections and immunotherapy-related complications must also be carefully monitored.