Primary Central Nervous System Lymphoma Mimicking Neuro-Behcet Disease

Neuro-Behcet’s disease (NBD) and primary central nervous system lymphoma (PCNSL) are rare conditions that can present with overlapping features, often delaying diagnosis. We report a female patient with recurrent oral aphthae and arthralgia who developed visual disturbances, behavioral changes, and hemiparesis. Brain magnetic resonance imaging (MRI) showed multiple contrast-enhancing lesions, and cerebrospinal fluid (CSF) analysis revealed elevated mononuclear cells. Extensive malignancy screening and autoimmune workup, including HLA-B51, were unremarkable. A presumptive diagnosis of NBD was made, and treatment with corticosteroids followed by infliximab led to initial improvement. Four months later, symptom recurrence with new MRI lesions and elevated CSF protein raised concerns. Lack of sustained response prompted a brain biopsy, confirming primary CNS large B-cell lymphoma. The patient was started on methylprednisolone and methotrexate, which were discontinued due to complications. Despite this, clinical improvement was observed, and the patient remains stable with mild cognitive deficits at follow-up four months later.