By: Greg Robert Zarelli, M.D.
A lumbar puncture (LP) is a major diagnostic tool sometimes used to confirm a diagnosis of MS. Also called a spinal tap, this is a test to analyze the fluid that surrounds the brain and spinal cord. This fluid, which acts like a cushion protecting the brain and spine from injury, is known as cerebral spinal fluid (CSF).
When we do the LP, we analyze the CSF and measure its protein, glucose and cell count. We also do an “MS Panel” which is a set of tests that simultaneously measure and compare the CSF and serum protein levels and immune system activity. In cases of MS, positive findings include oligoclonal bands in the CSF only and an elevated IgG index. An elevated IgG index, which indicates increased production of IgG within the central nervous system, is found in about 90 percent of MS cases.
What Can I Expect?
Usually, the person will lay on their side with their knees pulled up towards their chest. Sometimes, the test is done with the person sitting up, but bent over. The healthcare provider will clean the back and inject a local anesthetic to numb the lower spine. This may sting or burn slightly. A spinal needle is then inserted and fluid is collected. After the needle is removed, the area is cleaned and bandaged. The entire procedure usually takes about 30 minutes.
When is LP Needed?
LP is not always necessary when diagnosing relapsing forms of MS, but it can provide valuable data in cases where the diagnosis is questionable. CSF examination may be helpful in people presenting with their first demyelinating attack. The presence of oligoclonal bands in the CSF of these individuals suggests that they are at high risk for future attacks. LP may also be important when diagnosing primary progressive MS (PPMS) because certain treatable diseases can mimic PPMS. The LP helps to confirm the diagnosis and rule out those mimics.
Will it Hurt?
I tell my patients that an LP is scary but not at all dangerous, and most times, not even uncomfortable. The area in the low back where the needle is inserted is anesthetized and most people report feeling only some pressure.
What are the Primary Risks?
The biggest risks associated with LP are a post-LP headache; bleeding, especially in those taking blood thinners; and infection. To help minimize the chances of the former developing, I ask that all patients remain supine as much as possible for the first 24 hours after the LP. For a total of 48 hours after the LP, I request that they refrain from activities that could increase intra-thoracic, and thereby, intra-cranial pressure. Those activities would include but not be limited to: heavy lifting, exercise, sneezing, coughing, straining with a bowel movement, and sexual activity.
If a post-LP headache develops, that is, a headache that comes on with sitting and standing but is relieved with lying flat, I ask patients to try to stay supine, to drink plenty of fluids and to call me. If the headache persists for more than a few days, a simple procedure called a blood patch may be necessary.
What if I’m Very Nervous?
Occasionally, no matter how much reassurance I provide, some of my patients remain very nervous about the LP. In those cases, I suggest a little lorazepam (Ativan®), a sedative for short-term management of anxiety, before the LP to calm them down for the procedure. It usually works like a charm! Finally, I always ask that my patient have someone drive them to and from the procedure for safety purposes.
“Dr. Z” is Staff Physician in the Department of Neurology at Kaiser-Permanente NW in Clackamas, Oregon. When he’s not working, Dr. Z enjoys traveling and has visited 85 countries! He also enjoys running, weight lifting and the arts.
(Last reviewed 7/2009)