A lumbar puncture (also called a spinal tap) is a procedure that removes spinal fluid from the spinal canal. Testing the fluid may help your doctor pinpoint MS. Spinal fluid (also called cerebrospinal fluid) is a clear liquid produced in the ventricles of the brain. Its job is to protect and fill the cavities of the brain and spinal cord. The fluid contains sugar, proteins, and other substances that are found in the blood.
Tests performed on the spinal fluid look for evidence of inflammation in the CNS. Ninety percent of people with MS have elevated levels of antibodies or specific types of antibodies (called oligoclonal bands). Other CNS infections and inflammatory diseases can also cause these tests to be abnormal, so again, the test cannot be used as a definitive indicator of MS.
How do I prepare for a spinal tap?
No special preparations are needed before a spinal tap, which can be performed in your neurologist's office. But you should ask your doctor for specific guidelines about discontinuing alcohol use, aspirin products, or anticoagulant medications before the procedure. Tell your doctor if you have any allergies. It is also helpful to have your doctor explain what he is doing as he performs the procedure as it may serve to reduce your anxiety.
Of all the MS tests, the spinal tap is the most invasive and seems to generate the most anxiety. Although infrequent, complications can occur as a result of the spinal tap. For example, 5 to 30 percent of people who undergo a spinal tap get a headache, commonly referred to as a post-lumbar-puncture headache. Drinking plenty of fluids, especially caffeinated drinks, can help reduce your chances of getting a headache, as will lying flat for up to an hour after the procedure is done.
The procedure takes approximately 40 minutes. You will be asked to lie on your side in a fetal position, with your knees drawn as close as possible to your chest. Your neurologist will inject a local anesthetic into your lower back and once you are numb, he will insert a hollow needle into your lower back between two lumbar vertebrae. This may cause some minor discomfort or a slight burning sensation.
After the fluid is collected, the needle is removed and a bandage is placed over the area. The site may be a little sore for a day or two.