Cerebrospinal fluid (CSF) is a clear, colorless liquid that bathes the brain and spinal cord. While the primary function of CSF is to cushion the brain within the skull and serve as a shock absorber for the central nervous system, CSF also circulates nutrients and chemicals filtered from the blood and removes waste products from the brain. Examining the fluid can be useful in diagnosing many diseases of the nervous system, including MS.
CSF is obtained by doing a lumbar puncture or “spinal tap” — most often with the person lying on his or her side. After cleansing and injecting an anesthetic into the area, a long, thin, hollow needle is inserted between two bones in the lower spine and into the space where the CSF circulates. One to two tablespoons of the fluid are withdrawn through the syringe.
The CSF of people with MS usually contains:
Elevated levels of IgG antibodies, as well as
A specific group of proteins called oligoclonal bands.
Occasionally there are also certain proteins that are the breakdown products of myelin.
These findings indicate an abnormal immune response within the central nervous system, meaning that the body is producing an immune response against itself.
An abnormal immune response in CSF is found in a number of other diseases, so the test is not specific for MS;
Conversely, some 5-10 percent of patients with MS never show these CSF abnormalities.
Therefore, CSF analysis by itself cannot confirm or rule out a diagnosis of MS. It must be part of the total clinical picture that takes into account the findings of the person’s history and neurologic exam as well other diagnostic procedures.