CSF myelin basic protein levels in leptomeningeal metastases. Relationship to disease activity.

Myelin basic protein (MBP) was serially measured in 177 CSF samples of 33 patients with leptomeningeal metastases and in 34 cancer controls. The mean level in cancer controls (free of neural involvement) was 5.7 +/- 0.33 ng/ml (normal less than 5 ng/ml) with abnormal elevation of MBP detected in 17%. The activity of the leptomeningeal disease was classified as either acute-progressive, stable or in remission on the basis of clinical and CSF cytological findings. CSF MBP levels were analysed in each stage. Abnormal elevation of MBP was detected in 74% of the 68 samples obtained in the acute-progressive stage (mean +/- SEM: 18.25 +/- 1.4 ng/ml, P less than 0.0001), in 24% of the 79 samples in the stable phase (mean: 7.99 +/- 0.8 ng/ml, NS) and in 20% of the 30 samples in remission (mean 5.7 +/- 0.3 ng/ml, NS). Similar changes in levels of CSF MBP were also observed in longitudinal studies of patients responding to treatment or relapsing to the acute stage. Eight patients developed treatment induced necrotizing leukoencephalopathy with typical CT-scan findings; elevated levels of CSF MBP were detected in 7 of them (mean: 21 +/- 3 ng/ml) when measured within 2 weeks of diagnosis but not when measured 2 months earlier. Our study suggests that in leptomeningeal metastases, CSF MBP levels are indicators of the disease activity, particularly if longitudinal determinations are used.