Although there is no single test or set of tests that can establish a diagnosis of multiple sclerosis (MS), there are three tests that are generally considered useful:
- Magnetic resonance imaging (MRI)
- Visual evoked potentials (VEP)
- Cerebrospinal fluid (CSF) analysis
There are no laboratory tests that are completely specific for multiple sclerosis, but several laboratory tests are helpful in diagnosing or excluding this disease as the cause of a person's signs and symptoms. A few involve tests done on cerebrospinal fluid:
- CSF Electrophoresis and Isoelectric Focusing—these are two methods for separating the proteins in a biological fluid. A patient's CSF and serum are 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 that appear in the CSF and serum 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 people with MS 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 MS and several other diseases. It can also 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:
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—this is a major component of myelin. Increased concentrations of myelin basic protein 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 available; however, it may be used to assess disease activity in cases of established MS.
Health practitioners may also test for diseases that can cause symptoms similar to MS to determine if they may be responsible for a patient's illness. Examples include:
- Lyme disease
- Vitamin B12 deficiency
- Autoimmune disorders (e.g., lupus)
- MRI (magnetic resonance imaging) scans allow healthcare practitioners to examine the brain. MRI 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. Improvements in MRI technology have significantly improved the ability to accurately diagnose MS at an early stage. Early diagnosis and treatment is key to minimizing the effects of the disease.
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 Multiple Sclerosis 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 recordings of the nervous system's electrical response to visual stimuli. Damage to myelin can slow nervous system response time and VEP tests can reveal evidence of scarring along nerve pathways associated with vision. The NMSS web page has additional details about this test.
Two other types of evoked potentials may be used, though less commonly. Brain stem auditory evoked potentials (BAEP) is a test that helps detect lesions in the brainstem causing delays in the transmission of sounds. Somatosensory evoked potentials (SSEP) is a test that applies a brief electrical stimulus to the wrist or ankle. It detects disruptions in the pathways from the arms and legs to the brain at very specific points of the central nervous system.