Non-Hodgkin's Lymphoma of the Central Nervous System with N-Methyl-D-Aspartate Receptor Antibody Positivity - A Case Report.

Purpose: Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, among the paraneoplastic syndromes, is a recently characterized autoimmune encephalitis most commonly associated with antibodies against subunits of the NMDAR in the central nervous system. As a paraneoplastic syndrome, anti-NMDAR encephalitis is commonly associated with ovarian teratomas, small cell lung carcinomas and testicular germ cell tumors. To our knowledge, there have been no cases with primary central nervous system lymphoma (PCNSL), a rare type of extranodal non-Hodgkin's lymphoma, without lymph node involvement associated with anti-NMDAR encephalitis.

Case Report: A 58-year-old right-handed male patient with complaints of instability in walking for two months, progressively smaller handwriting, hallucinations when falling asleep or waking up, decreased memory, inability to maintain attention was admitted to our hospital for further diagnosis and treatment. Lumbar puncture was performed with the diagnosis of possible encephalitis after many further examinations and CSF studies revealed NMDAR antibody positivity, leading to the initial diagnosis of anti - NMDAR encephalitis. He was treated with high dose methylprednisolone and intravenous immunoglobulin. Due to the continuation of the patient's presenting symptoms and cranial magnetic resonance imaging findings, a stereotactic brain biopsy was performed from the area with contrast enhancement and the diagnosis was revised as PCNSL associated with NMDAR antibody positivity.

Conclusion: This report emphasizes the importance of anti-NMDAR encephalitis as a paraneoplastic syndrome in previously undiagnosed PCNSL. Therefore, it is crucial to be aware of anti-NMDAR encephalitis as a paraneoplastic neurological syndrome that can present with non-Hodgkin's lymphoma. It is necessary to continually observe the evolution of the disease and perform further diagnostic tests for early identification.