Exclusion of leukaemic meningitis by quantitation of T and B lymphocytes in cerebrospinal fluid.

Involvement of the central nervous system (CNS) in chronic lymphatic leukaemia (CLL) is rare. However, when a patient with CLL presented with meningeal symptoms and a high CSF lymphocyte count in the absence of identifiable infection, meningeal leukaemia was considered the most likely diagnosis. Subsequent quantitation of T and B lymphocytes in the blood and CSF was found to be a most valuable aid in excluding the diagnosis, and later a cryptococcal infection was proven. This case is reported to draw attention to the value of T and B lymphocyte quantitation where difficulty is experienced in interpretation of cells in CSF in patients with leukaemia or lymphoma.