Primary CNS Lymphoma vs. Tumefactive Multiple Sclerosis: A Diagnostic Challenge.

Primary CNS (central nervous system) lymphoma is a rare condition with the incidence of less than 1% of all non-Hodgkin lymphomas (NHLs) and approximately 2% of all primary brain tumours. Diagnosis can be challenging and necessitates brain biopsy for definitive diagnosis. A 41-year male presented with history of impaired cognition, facial asymmetry, visual impairment and left sided body weakness. MRI brain demonstrated multiple enhancing lesions with one larger lesion in right basal ganglia with surrounding oedema and mass effect. These findings suggested the differential diagnoses of tumefactive multiple sclerosis (MS), primary CNS lymphoma (PCNSL) and tuberculosis. The patient had normal CT chest, abdomen and pelvis, normal CSF examination and cytology, negative CSF oligoclonal bands (OCBs) and negative HIV screening. It was impossible to differentiate between tumefactive MS and PCNSL without undertaking brain biopsy. Diffuse large B cell lymphoma (DLBCL) was the final diagnosis. Diagnosing PCNSL can be challenging and brain biopsy should not be delayed for definitive diagnosis and targeted treatment.