Lymphocytosis in the cerebrospinal fluid of a patient with chronic lymphocytic leukemia: the value of immunologic analysis

ABSTRACT

The distinction of lymphomatous or leukemic lymphocytes from reactive lymphocytes in the cerebrospinal fluid (CSF) is of great clinical significance and is usually readily accomplished on morphologic grounds. However, the "malignant" lymphocytes of chronic lymphocytic leukemia (CLL) are mature and therefore closely resemble reactive lymphocytes in cytocentrifuged CSF preparation. We recently studied a patient with CLL [white blood cell (WBC) count of 30,700/μL with 72% lymphocytes] who developed a prominent lymphocytosis in the CSF (WBC, 1,700 μL with 98% lymphocytes). The morphology of the CSF lymphocytes suggested leukemic involvement of the central nervous system (CNS); however, immunologic analysis was not confirmatory. The peripheral blood lymphocytes were demonstrated to be monoclonal for kappa light chains consistent with a B-cell lymphoproliferative disorder, whereas 95% of the lymphocytes in the CSF were positive for T₁₁ antigen, a marker for mature T-cells. This report demonstrates the utility of immunophenotyping studies as an adjunct to the differential diagnosis of neoplastic versus nonneoplastic involvement of the CNS in disorders such as CLL in which morphologic differentiation may be difficult.