Selected ion monitoring technique for the evaluation of sterols in cerebrospinal fluid: a new approach to desmosterol test for central nervous system tumors.

The desmosterol test for the diagnosis of central nervous system (CNS) tumors is proposed in a simplified form. The procedure is based upon the analysis of sterol profile in cerebrospinal fluid (CSF) by selected ion monitoring (SIM) technique. Applied to 55 patients with tumoral and non tumoral CNS disease, the new test detects average levels of CSF desmosterol in tumor bearing patients that are tenfold higher than in the absence of CNS neoplasia. On an individual basis, a concentration of CSF desmosterol equal to or higher than the mean plus twice the standard deviation for the reference group of patients with no CNS tumor, is considered a positive result. Based on this criterion, a correct diagnosis was made in 73% of cases vs 77% of the former test, which required a 5-day treatment period with a desmosterol-reductase inhibitor in order to increase CSF desmosterol concentration. With this revised procedure CSF desmosterol can be detected in smaller volumes of CSF without any drug pretreatment, thus making the test more suitable for clinical application.