MONOCLONAL B-CELL POPULATION MIMICKING LYMPHOMA IN A PATIENT WITH MULTIPLE-SCLEROSIS

Background.-Diagnosis of intraparenchymal brain lesions has usually re quired invasive diagnostic procedures, because too few cells are shed into cerebrospinal fluid to permit cytologic diagnosis. Polymerase cha in reaction technology makes it possible to identify cell populations that are present at a much lower frequency than traditional techniques . Case Report.-A young woman presented with multiple brain lesions rai sed the question of primary central nervous system lymphoma. Polymeras e chain reaction analysis of cerebrospinal fluid showed evidence of a monoclonal B-cell population, heightening suspicion of lymphoma. Brain biopsy showed acute demyelination most consistent with multiple scler osis. Conclusion.-Although T-cell restriction has been demonstrated in multiple sclerosis lesions, the finding of a monoclonal B-cell popula tion was unexpected and to our knowledge has not been previously repor ted. This case emphasizes that monoclonality is not always indicative of a neoplastic process, particularly in the central nervous system.