Cerebrospinal Fluid (CSF)
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.
Fluid Obtained by ‘Spinal Tap’
CSF is obtained by doing a lumbar puncture or “spinal tap.” 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 One to two tablespoonfuls of the fluid are then withdrawn.
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 autoimmune response within the central nervous system, meaning that the body is producing an immune response against itself.
Other Tests Also Needed
An abnormal autoimmune response in CSF is found in a number of other diseases, so the test is not specific for MS. Conversely, some 5-10% 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 on the person’s history and neurologic exam, other diagnostic procedures such as evoked potentials and magnetic resonance imaging (MRI).