Zilla is corrcect. The presence of Myelin Basic Protein in the CSF is a sign of any kind of damage in the central nerous system. It is very nonspecific. The damage can be from MS, other neuro diseases, infection, surgery or trauma. In the context of MS, as Zilla said, MBP is often - but not always - seen during a relapse and may dwindle away or become negative during remission. The problem is that many people in relapse do NOT have a + MBP, so it is not a good biomarker to show a relapse.