Isolated central nervous system relapse in acute monocytic leukemia diagnosed by FISH and cell marker analysis of cerebrospinal fluid cells

Abstract

To diagnose central nervous system (CNS) infiltration in leukemia, the presence of blasts in the cerebrospinal fluid must be confirmed. If the presence of blasts cannot be determined, it is difficult to diagnose CNS infiltration. A nine-month-old girl was diagnosed as having acute myeloid leukemia M5a with KMT2A (MLL) rearrangement. This cannot be detected by partner genes without CNS infiltration. She then received standard chemotherapy. She developed recurrent vomiting and convulsions and was suspected to have a relapse of CNS infiltration five months after discharge. However, it could not be diagnosed by cerebrospinal fluid cytopathology. We carried out KMT2A fluorescence in situ hybridization (FISH) and flow cytometry (FCM) analysis, which showed the proliferation of monoclonal monocytic cells with KMT2A split signals. On the basis of these findings, we were able to make a definitive diagnosis. Monocytic leukemia blasts are known to migrate into tissues, differentiate, and proliferate. FISH and/or FCM analysis may be useful when it is difficult to diagnose a relapse of CNS infiltration by cytopathology.