A spinal tap (also known as lumbar puncture) is one of the tests used to diagnose multiple sclerosis (MS). The test is done in a hospital or clinic setting where a small sample of the cerebrospinal fluid (CSF) is collected, using a thin needle, from the lower lumber region (lower back). A sample that shows abnormal results in proteins and inflammatory cells may indicate MS.
Besides MS, this test is used to confirm conditions such as meningitis, Guillain-Barre syndrome, or brain and spinal cord cancers.
Getting a spinal tap
CSF is clear liquid that acts as a cushion, protecting the brain and the spinal cord. Usually, this fluid is colorless and has the same consistency as water. Nutrients, and substances as well as waste products from the brain, move through cerebrospinal fluid.
Before the test, your may be asked to take a computerized tomography (CT) or a magnetic resonance imaging (MRI) scan to make sure that this test is necessary. Tell your doctor if you’re taking blood-thinning medication (anticoagulants).
You will be asked to wear a hospital gown and likely will be told to lie on your side with your legs pulled up to the chest. The position flexes and spreads the vertebrae, so the doctor can more easily insert a needle between two lower lumbar-region vertebrate. (You will have already be given a local anesthetic to numb the area.) A thin, hollow needle is inserted, passing between vertebrate and through the spinal membrane into the spinal canal.
CSF pressure is measured, and a small fluid sample is collected for analysis, then another measure of fluid pressure is taken. While the needle is in, you may feel some pressure in your back. While the needle is being placed, you may also feel a sudden and brief, sharp pain in a leg, should the needle touch a nerve in the canal.
A bandage will be placed over the site, and you may be told to lie still for a while to reduce the change of post-procedure headaches.
The entire procedure lasts about 45 minutes, and it usually takes less than 2 days for your body to naturally replace lost fluid.
Possible side effects
Spinal tap tests are typically very low risk. However, some people may experience any of these side effects:
- Headache. This is the most common side effect, and it usually starts a day or two after the test. It can last from a few hours to a week or more. Headaches are usually worse while standing or sitting, and can be accompanied nausea, vomiting or dizziness. They are best treated with bed rest, drinking fluids, and simple painkillers.
- Back pain. Some people may have lower back pain after the test. Usually, the pain is confined to the area where the needle penetrated, but pain can also be felt in the legs.
- Bleeding. There is a risk of bleeding near the area where the needle was inserted. In rare situations, bleeding can occur in the epidural area in the spine itself.
Spinal tap and MS diagnosis
After the CSF sample is collected, the sample is sent to laboratory to test for immune cells, antibodies, and other proteins that indicate an abnormal immune system response within the central nervous system, a sign that the body is attacking itself.
Results indicating MS may include:
- Presence of oligoclonal bands, a group of proteins (called immunoglobulins) that show inflammation in the central nervous system.
- High levels of immunoglobulin G (IgG) antibodies. People with low levels of IgG are more prone to infections.
- Other proteins resulting from the breakdown of myelin (the fatty substance that surrounds and protects nerve cells) may also be present.
Although a spinal tap is used in diagnosing MS, it is not specific to this disease. Other tests need to be considered before a confirmed diagnosis of MS can be made.
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