[Contribution of biology to diagnosis of multiple sclerosis]

The analysis of the cerebrospinal fluid is the only biological test included in the diagnostic criteria for MS. A search for intrathecal IgG synthesis by isoelectrofocussing should always be performed when the cerebrospinal fluid is analyzed for a possible diagnosis of MS. Intrathecal IgG synthesis is detected in about 95 p. 100 of MS cases. However, it is not specific for MS and only signs the inflammatory nature of the nervous system lesions. In our opinion, analysis of the CSF should be proposed systematically for primary progressive MS, in most cases of monosymptomatic demyelinating syndromes, and according to the clinical context and the result of the MRI analyses in the remaining forms. To date, no prognostic criteria can be drawn from the analysis of the CSF. Other biological tests can be performed in order to eliminate other diagnosis. These tests only have a great interest in atypical forms of the disease.