[Terminal deoxynucleotidyltransferase (TdT)-positive cells in cerebrospinal fluid of children with leukemia or non-Hodgkin lymphoma: implications for the diagnosis of central nervous system leukemia].

Identification of terminal deoxynucleotidyl transferase (TdT) positive cells in sites other than bone marrow, thymus, lymph nodes and peripheral blood is indicative of a TdT positive lymphoproliferative disease. We therefore employed both a TdT-immunofluorescence (IF) assay and conventional cytomorphology to examine the cells in 421 cerebrospinal fluid samples from 60 children with a TdT positive acute lymphoblastic leukemia or non-Hodgkin lymphoma, at diagnosis as well as during follow-up. The results of the TdT assay were compared with those obtained by cytomorphological analysis of the same sample. The authors conclude that the TdT-IF assay is a valuable additional tool in diagnosing TdT positive central nervous system leukemia. It offers more reliable and conclusive diagnoses than cell count and cytomorphology alone, which might avoid both under- and overtreatment of the patient.