Flow cytometry as a diagnostic tool in lymphomatous or leukemic meningitis: ready for prime time?

In patients with neoplastic meningitis (NM), early diagnosis is highly desirable because the rapid institution of intrathecal therapy may mitigate the course of the disease. Cytology, long considered the "gold standard" for diagnosis, has low sensitivity because of both the paucity of cells in the cerebrospinal fluid (CSF) and morphological similarities between benign and malignant cells. A comprehensive review of the literature from 2005 through 2011 was performed that focused on diagnostic modalities for lymphomatous meningitis. Several studies demonstrated the sensitivity of flow cytometry to be several-fold higher than that of cytology for the detection of CSF leukemia/lymphoma. Patients with negative cytology but positive flow cytometry results are often asymptomatic and have lower CSF cell counts and neoplastic B-cell percentages compared with patients with positive cytology findings. Flow cytometry is a highly sensitive technique capable of accurately detecting malignant cells, even in samples with very low cell counts. Flow cytometry allows for the earlier detection of NM before the onset of clinical symptoms and CSF pleocytosis and therefore may enable more effective treatment. Future consensus regarding standardized flow cytometric antibody panels, with uniform definitions of positivity, is likely to further advance the early detection of NM by flow cytometry and permit broader clinical applicability.