Multiple Sclerosis: Getting Through a Spinal Tap
When combined with other neurological tests, a spinal tap may help confirm an MS diagnosis. Here’s what to expect from the procedure.
In many if not most cases, multiple sclerosis (MS) can be diagnosed on the basis of a person’s symptoms, along with an MRI of the brain and spinal cord. But when a neurological exam and MRI aren't conclusive, a spinal tap, also known as a lumbar puncture, is sometimes done to help confirm — or substantiate — an MS diagnosis, says Barbara Giesser, MD, a multiple sclerosis specialist with Pacific Neuroscience Institute and professor emeritus of clinical neurology at the David Geffen UCLA School of Medicine.
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In a spinal tap, a sample of cerebrospinal fluid — the fluid that surrounds the brain and spinal cord — is removed and analyzed for specific antibodies and proteins that are characteristic of multiple sclerosis. However, you cannot 100 percent confirm or rule out MS based on a spinal tap, explains Dr. Giesser. “Even if the spinal tap is negative, about 10 percent of people who have MS have normal spinal fluid. And if it’s positive, other things [other than MS] can cause a positive result,” she says.
Like any invasive procedure, a spinal tap comes with certain risks, and doctors have to weigh those risks with the potential benefits when ordering one.
Undergoing a Spinal Tap
Before you have a spinal tap, your doctor will order blood tests to check for any bleeding or clotting disorders. If you’re taking blood thinners or painkillers such as ibuprofen and aspirin, tell your doctor. You will probably have to stop taking them before the procedure.
Spinal taps most commonly take place at an outpatient facility. You’ll be asked to put on a hospital gown and either lie on your side with your knees drawn up or sit leaning forward on a stable surface. These positions flex your back and widen the spaces between your vertebrae, making it easier to insert a needle.
Your back will be washed and covered with a sterile sheet, and a local anesthetic will be injected into your lower back to numb the puncture site. Typically, this is the only painful part of the procedure. “Spinal taps are usually uncomfortable but seldom extremely painful,” notes Giesser.
When the needle used to remove spinal fluid is inserted through your spinal membrane and into the spinal canal, you may feel pressure in your back, but this part of the procedure is usually painless. Some people may feel some burning and nerve twinges when the needle is inserted. You may be asked to shift your position slightly to help the doctor correctly position the needle. A small amount of cerebrospinal fluid is then collected in a sterile container and sent to a lab for analysis.
When the needle is removed, a bandage is put on the entry site, and you’ll lie down for a while before leaving the medical facility. From start to finish, a spinal tap takes about a half hour.
In some cases, such as if you are overweight, have degenerative bone disease, or a spinal deformity, a spinal tap using fluoroscopy — a type of medical imaging using a continuous X-ray image — may be recommended, Giesser notes.
Can a Spinal Tap Cause Paralysis?
While a spinal tap can be uncomfortable, the fear of a spinal tap causing paralysis is unfounded. Paralysis can occur when the spinal cord, which runs from the brain stem to the top of the lumbar vertebrae and usually ends in the space between the first and second lumbar vertebrae, is damaged. During a spinal tap, the needle is injected between the third and fourth or fourth and fifth lumbar vertebrae in the lower back, too low to pierce the spinal cord.
Side Effects and Complications
Some people develop a headache — called a “spinal headache” — after a spinal tap. Spinal headaches usually start within a day or two after a lumbar puncture but can occur several days later. They are thought to result from an internal leak at the puncture site, which is believed to cause pressure changes in the cerebrospinal fluid that can be sensed by the dura mater, the tough membrane that surrounds the spinal cord.
You’ll know it’s a spinal headache if the pain goes away when you lie down but reappears when you sit or stand.
Home remedies for a mild spinal headache include:
- Lying down in a comfortable position
- Drinking liquids
- Taking an over-the-counter analgesic, such as acetaminophen
- Studies have shown that caffeine can also be helpful, according to a review published in April 2020 in Current Pain and Headache Reports.
Let your doctor know if you develop a headache following a spinal tap, particularly if your pain or any other symptoms such as nausea are severe or get progressively worse.
According to Orhun Kantarci, MD, a professor of neurology at the Mayo Clinic in Rochester, Minnesota, spinal headaches usually last no longer than three days, and they usually go away on their own.
However, Dr. Kantarci says, about 4 percent of people with a spinal headache require what's called a blood patch. For that, a doctor draws blood from your arm and injects it into the area of the lumbar puncture to cause the leakage to clot.
Other potential complications of a spinal tap include infection and bleeding, but both are rare. If you experience signs of infection such as fever, severe neck stiffness, and pain or redness at the puncture site, however, contact your physician immediately.