There are no laboratory tests that are completely specific for multiple sclerosis. However, several laboratory tests generate abnormal results in patients with MS and are helpful in diagnosing or excluding this disease. The most useful tests look for evidence of immunoglobulin G (IgG) production within the central nervous system. They include:
- CSF Analysis. Evalutes physicial and chemical aspects of the CSF that may be altered by MS.
- Cerebrospinal Fluid (CSF) Electrophoresis and Isoelectric Focusing. Electrophoresis and isoelectric focusing are two methods for separating the proteins in a biological fluid. A patient’s CSF and serum evaluated side-by-side on a test surface using either of these two techniques. Following the separation step, a protein stain is applied to both specimens, and the banding patterns of the proteins in CSF and serum that appear are compared to one another. The presence of two or more IgG bands in CSF that are not present in serum is a positive test for oligoclonal banding. About 90% of MS patients show oligoclonal banding in their CSF.
- CSF Immunoglobulin G (IgG) Index. Increased levels of CSF IgG can be due to excess production of IgG within the central nervous system, which is seen with multiple sclerosis and several other diseases, or they can be due to leakage of plasma proteins into the CSF, such as might occur with inflammation or trauma. To discriminate between these two possibilities, the IgG index is calculated from IgG and albumin measurements performed in CSF and serum. The calculation usually takes the following form:
IgG index = [IgG (CSF) / IgG (serum)] / [Albumin (CSF) /Albumin (serum)]
An elevated IgG index indicates increased production of IgG within the central nervous system. It is found in about 90% of MS cases.
- Myelin basic protein is a major component of myelin. Increased concentrations of myelin in CSF indicate that demyelination is taking place. This process is not specific for MS, as other inflammatory diseases of the central nervous system can also elevate the amount of myelin basic protein in CSF. This test is not widely used; however, it may be used to assess disease activity in cases of established MS.
- MRI (magnetic resonance imaging) scans allow doctors to literally see into the brain. They can show both permanent scarring as well as new lesions. These scans are used to help diagnose MS and to track its progression over time. In addition to the standard MRI, there are a variety of specialized techniques that may be performed, such as functional MRI, magnetic resonance spectroscopy, and diffusion-tensor MRI. The National MS Society (NMSS) web site has more information on the use of MRI in MS.
- Visual evoked potentials (VEP) are electrical diagnostic studies that measure the speed of nerve transmissions (messages) in various parts of the brain. They are sensitive to MS damage and can detect evidence of scarring along nerve pathways. The NMSS webpage has additional details about this test.