Central nervous system involvement in acute nonlymphocytic leukemia. A prospective study of adults in remission.

To identify adults with acute nonlymphocytic leukemia at risk for the development of central nervous system involvement, we performed periodic cerebrospinal fluid examinations on patients in remission. Among 58 consecutive patients monitored during first remission, central nervous system leukemia developed in nine (16 percent). Four patients, including one who was symptomatic, had central nervous system leukemia detected simultaneously with marrow relapse. Five additional patients were asymptomatic and continue to have bone marrow remission. Following central nervous system and systemic treatment, two of these five patients have never had relapse, and three had relapse in the bone marrow five, 10, and 21 months later. Factors at diagnosis associated with the subsequent development of central nervous system leukemia were elevated leukocyte count, serum lysozyme and lactate dehydrogenase, extramedullary infiltration including splenomegaly, and monocytic (FAB M4 or M5a) morphology. In six of 17 patients (35 percent) with monocytic morphology, central nervous system leukemia developed compared with only three of 41 patients (7 percent) with other subtypes (p = 0.02). Discriminant analysis identified leukocyte count, splenomegaly, and M4 or M5a morphology as the most important risk factors and led to a mathematical formula that correctly identified 90 percent of the patients. Although the risk of central nervous system leukemia in adults with acute nonlymphocytic leukemia is too low to justify routine prophylaxis, those patients recognized to be at a greater risk should receive prophylaxis or be monitored closely with periodic lumbar punctures.