Multiple Sclerosis and the Spinal Tap

Medically Reviewed by Arefa Cassoobhoy, MD, MPH on March 24, 2023
3 min read

Your brain and spinal cord are bathed in fluid. A lumbar puncture, also called a spinal tap, is a procedure doctors use to remove and test some of this liquid, called cerebrospinal fluid (CSF).

It helps them diagnose disorders of the brain and spinal cord, including multiple sclerosis.

The results of the procedure can help doctors see whether your body’s immune system is attacking itself, which is what happens in multiple sclerosis. If you have the condition, your CSF (spinal fluid) will have higher amounts of certain proteins.

If someone’s CSF doesn’t have these proteins, though, they might still have multiple sclerosis -- 5% to 10% of people with the condition never show signs in their spinal fluid.

Also, these signs can show up in a number of other diseases, too. So a spinal tap by itself can't confirm or rule out a diagnosis of multiple sclerosis. It must be part of the total picture of testing for the disease.

You don’t have to do anything to get ready, unless your doctor gives you special instructions.

In most cases, you’ll need to stop taking any blood thinner medicines, including aspirin, for a few days beforehand. And if you're allergic to latex or any medications, tell your doctor.

To start, you’ll lie on your side with your knees drawn as close to your chest as possible. Or you'll sit with your arms and head resting on a table.

After the skin around your lower back is cleansed and covered, you’ll get medicine to numb that part of your body. Your doctor will put a long, thin hollow needle in your low back between two bones in your lower spine below the bottom of the spinal cord where there is still a sac full of fluid. They’ll take 1-2 tablespoons of fluid and remove the needle. The procedure doesn’t touch your spinal cord.

You’ll need to lie on your back or stomach for a few hours. You also may need to give a sample of your blood for testing, too.

Avoid intense exercise for a day or so after the procedure.

Yes. But just like most tests, there are a few minor risks. These include:

  • Headache. About 10% of people get a spinal headache -- one that gets worse when you sit or stand and feels better instantly when you lie down. If you get one, lie down as much as possible and drink plenty of fluids.
  • Infection. But the risk is very low.
  • Bloody tap. Sometimes the procedure may pierce a small blood vessel, so blood mixes in with the CSF. You won’t need treatment for it, but in some cases, you may need another spinal tap later on to get a "clear" sample.

Call your doctor right away if you notice any unusual drainage, including bloody discharge, or pain that gets worse.