Initial and follow-up evaluations on cerebrospinal fluid involvement by hematologic malignancy.

Central nervous system (CNS) involvement is a serious complication in hematologic malignancy, and early detection and management of CNS involvement in these cases significantly impact the prognosis. Currently, there is no consensus on the use of multiparametric flow cytometry (MFC) and conventional cytology (CC) testing for initial and follow-up cerebrospinal fluid (CSF) specimens to diagnose CNS involvement by hematologic malignancy. In our institution, after initial MFC and CC, two subsequent negative MFCs are required before discontinuing MFC. The aim of this study is to evaluate the outcome of this approach. CSF cytology and MFC reports were retrieved from Laboratory Information System, and data was reviewed. Between January 2020 and December 2021, 1789 CSF samples from 280 patients were submitted for CSF analysis. For those 517 CSF samples tested by both MFC and CC, 97 cases tested positive by both MFC and CC with 95% concordance. Eighteen cases were MFC + /CC - and 7 were MFC - /CC + . Thirty-six cases had initially positive MFCs followed by more than one MFC evaluation. Among those 36 cases, 22 cases (61.1%) converted to negative after the second follow-up sample, 9 cases (25%) were continuously positive for at least three samples, and 5 cases (13.9%) exhibited negative to positive conversion. Compared to negative CSF cases, positive CSFs had higher total nucleated cell count and higher total protein levels while red blood cells, glucose, and lactate dehydrogenase levels remained at comparable levels. The concordance between MFC and CC was excellent. The high incidence of positive MFCs on two or more follow-up samples and the high frequency of negative MFC to positive conversion indicate the necessity of repeated negative MFCs before discontinuing MFC. The fact that more than half of the positive cases converted to negative after the second CSF specimen and most follow-up positive cases can be detected by CC alone suggests it is adequate to use CC alone for follow-up CSF study after two consecutive negative MFCs.