Recognition of central nervous system leukemia by flow cytometry

Cerebrospinal fluid of 24 patients with acute leukemia was studied by DNA/RNA flow cytometry. In six of 15 patients with central nervous system (CNS) relapse, the spinal fluid cells had abnormal DNA stemlines, ranging from near haploid to hyperdiploid. In two additional cases, leukemic cells were identified by a abnormally high RNA content only. One patient had two different aneuploid cell populations in spinal fluid not distinguished by cytologic morphology. Another patient with initial diploid leukemia had CNS relapse characterized by the same DNA stemline long after a triploid DNA stemline emerged in the marrow. DNA/RNA flow cytometry detected leukemic cells that were not identified (“uniform” or “reactive”) by cytological criteria in 5/6 patients studied and in addition differentiated lymphoblastic from nonlymphoblastic cell types according to low and high RNA content.