Clinical significance of monoclonal B cells in cerebrospinal fluid.

BACKGROUND

Morphologically malignant lymphocytes in the cerebrospinal fluid (CSF) are highly suggestive of central nervous system involvement by lymphoid malignancy. Although flow cytometry is increasingly used to detect a monoclonal B-cell population in the CSF, the significance of this finding in the absence of morphologically identifiable malignant cells is unknown.

METHODS

We reviewed CSF flow cytometric results in 32 patients studied at a single institution over 5 years and identified patients who had monoclonal B-cells in the CSF. Clinical presentation and course were reviewed.

RESULTS

Twelve patients had a monoclonal B-cell population in the CSF, but only three had clinical evidence of malignant CNS disease. Of the other nine patients, 4 had nonmalignant neurologic disease and five had a lymphoproliferative disorder: chronic lymphocytic leukemia (n = 4) and mantle cell lymphoma (n = 1). In patients who had chronic lymphocytic leukemia and mantle cell lymphoma, the monoclonal B-cell population was small and had an immunophenotype identical to that of circulating malignant B cells. None of these nine patients developed clinical evidence of malignant CNS involvement during follow-up.

CONCLUSION

In patients who have indolent B-cell malignancies, the presence of monoclonal B cells in the CSF may not be diagnostic of clinically significant CNS involvement by a lymphoid malignancy.