CSF testing for multiple sclerosis.

New diagnostic criteria for multiple sclerosis (MS) were published in 2001 by McDonald and colleagues. These criteria take account of the clinical features, brain and spinal-cord MRI findings, CSF findings, and visual evoked-potential studies. The McDonald criteria define rigorous MRI requirements but do not define an optimum CSF test for the diagnosis of MS. CSF testing should be optimised, because, in the McDonald criteria, a positive CSF study is an essential diagnostic criterion in patients who have objective clinical evidence of only one lesion and only a few MRI lesions, and it is a mandatory criterion for the diagnosis of primary progressive MS. The rationale underpinning the use of CSF testing is the determination of whether there is synthesis of immunoglobulin G (IgG) in the CNS compartment (intrathecal synthesis). This indicates expansion of B cells in the CNS and is a characteristic feature of MS. In the McDonald criteria, a positive CSF study is defined as one showing either oligoclonal IgG bands or a high IgG index, which are two different indicators of intrathecal IgG synthesis. These indicators differ in sensitivity and specificity, and there are also differences in the techniques of CSF analysis.