POLYMERASE CHAIN-REACTION ON CEREBROSPINAL-FLUID CELLS IN THE DETECTION OF LEPTOMENINGEAL INVOLVEMENT BY B-CELL LYMPHOMA AND LEUKEMIA - A NOVEL STRATEGY AND ITS IMPLICATIONS

In the search of B-cell lymphoma/leukaemia dissemination to cerebrospi nal fluid (CSF), we used the highly sensitive semi-nested PCR (snPCR) for the analysis of IgH gene rearrangements. This method detects a rea rranged IgH gene from a single B lymphocyte which may or may not repre sent the neoplastic B-cell population. We therefore performed multiple snPCR (three to five) experiments on the same CSP sample, postulating that the detection of a band of the same size and sequence in differe nt PCR runs was highly indicative of a clonal population. 17 consecuti ve cases with a differential diagnosis of primary (PCNSL) (n=10) or se condary (SCNSL) (n=7) CNS lymphoma or leukaemia were investigated by t he new strategy. The clonal nature of the B-cell population was confir med in 3/10 of suspected PCNSL, and in six other cases the PCR study w as indicative of reactive lymphocytosis. One case revealed a clonal B- cell population in the clinical context of an autoimmune disorder. Evi dence of clonal B-cell population was found in 4/7 of suspected SCNSL. In one of these cases the detected band and its sequence proved ident ical to that of the primary nodal lymphoma. We believe that the evalua tion of B-cell clonality in CSF requires multiple snPCR amplification on the same sample to compare the size of the products and, if necessa ry, the DNA sequences to ascertain the diagnosis of malignancy in equi vocal cytologic and clinical findings.