Your brain and spinal cord are bathed in spinal fluid. A spinal tap, also called a lumbar puncture, is a procedure that removes and tests some of this fluid to help diagnose disorders of the brain and spinal cord, including multiple sclerosis.
The fluid, called cerebrospinal fluid (CSF), contains glucose (sugar), proteins, and other substances that are also found in the blood. Analysis of the fluid includes looking at the number and types of white blood cells (infection fighting cells), the level of glucose, the types and levels of various proteins (especially immune system proteins called antibodies or immunoglobulins), and testing for bacteria, fungus, or abnormal cells.
How Does a Spinal Tap Help Diagnose Multiple Sclerosis?
A spinal tap that reveals a large number of immunoglobulins (antibodies) as well as oligoclonal bands (the pattern of immunoglobulins on a more specific test) or certain proteins that are the breakdown products of myelin is suggestive of MS. These findings indicate an abnormal autoimmune response within the brain and spinal cord, meaning that the body is attacking itself.
Over 90% of people with MS have oligoclonal bands in their CSF. While increased immunoglobulin in the CSF and oligoclonal bands are seen in many other brain and spinal cord conditions, their presence is often useful in helping to establish a diagnosis of MS.
However, a "negative" spinal tap does not rule out MS or other diseases; some 5% to 10% of people with MS never show CSF abnormalities. And, an abnormal autoimmune response in CSF is found in a number of other diseases, so the test is not specific for MS. Therefore, a spinal tap by itself cannot confirm or rule out a diagnosis of MS. It must be part of the total picture that takes into account other diagnostic procedures such as evoked potentials and magnetic resonance imaging (MRI).
How Do I Prepare for a Spinal Tap?
No preparation is needed for a spinal tap unless your doctor gives you special instructions. In most cases, you will be asked to stop taking any blood thinners, including aspirin, for a number of days before your spinal tap. If you are allergic to latex or any medications, tell your doctor.