Cerebrospinal fluid B2-microglobulin levels in meningeal involvement by malignancy

Cerebrospinal fluid (CSF) and serum B2-microglobulin (B2m) levels were measured prospectively in 63 patients with hematological malignancies and 14 patients with solid tumours to evaluate the correlation between elevated levels and malignant infiltration of meninges. Serial CSF B2-m levels were also measured in 18 patients who received prophylactic intrathecal cytotoxic treatment. CSF B2-m levels were significantly higher in patients with central nervous system (CNS) involvement than in those without (p less than 0.001). A CSF B2-m level greater than 1.80 mg/L was closely associated with CNS disease (specificity 96%, sensitivity 76%) and CNS infiltration was also likely when the CSF B2-m level exceeded a simultaneously drawn serum level (specificity 98%, sensitivity 46%). Intrathecal methotrexate prophylaxis resulted in a consistent and significant rise in CSF B2-m levels with an average increase of 96% during a course of intrathecal injections. These results suggest that CSF B2-m levels may not be helpful for predicting early CNS relapse in these patients. However the CSF B2-m level and the corresponding serum B2-m level is a useful adjunct to the cytological diagnosis of CNS involvement by malignancy at presentation. Its value in predicting early CNS relapse and documenting response to CNS treatment requires further clarification.