| I couldn't resist the title's corny riff on the name of the | | | | you sign a permission form. In this author's opinion, |
| rock band and their movie, but the kind of spinal tap | | | | lumbar puncture is the most benign test for which |
| featured in this article was a spinal tap before Spinal | | | | written permission is traditionally required and is less |
| Tap was Spinal Tap. (Does that make any sense?) | | | | risky than some other procedures--like drawing blood |
| Known more formally as a lumbar puncture, this kind | | | | from a high-pressure artery--for which written |
| of spinal tap is a valuable medical test with an | | | | permission is traditionally omitted. |
| interesting history. In 1891 Heinrich Quincke, of Kiel, | | | | The next step is to lie on your side on a bed or |
| Germany, introduced this procedure as we know it | | | | procedure table with your knees tucked up to your |
| today. His original intent was to help babies suffering | | | | chest. The skin of your lower back is painted with an |
| from hydrocephalus (water on the brain) by draining | | | | iodine-based solution to produce a sterile field. If you |
| away excess fluid, but from the outset he was also | | | | have an allergy to iodine, an alcohol-based solution is |
| interested in lumbar puncture's use as a diagnostic tool. | | | | substituted. The surrounding area is then covered with |
| To understand the usefulness of this test and why | | | | sterile paper or cloth. The skin and the tissue beneath |
| you might someday need to have one, a little | | | | the skin are then numbed with local anesthetic, and |
| background is helpful. The brain and spinal cord are | | | | then everything is ready to insert the spinal needle. |
| wrapped in a membrane called the meninges. Within | | | | The reason the lower back (lumbar spine) is chosen is |
| the meninges, a watery fluid called the cerebrospinal | | | | because here the sac of meninges can be entered |
| fluid (CSF) bathes the inside and outside of the brain | | | | without risk of poking a hole in the spinal cord. This is |
| and the outside of the spinal cord. Within the brain's | | | | because the spinal cord ends several inches higher |
| fluid chambers (ventricles), the body perpetually | | | | within the spinal canal. The composition of the CSF is |
| manufactures new CSF from constituents of the | | | | nearly the same throughout its system. Thus, CSF |
| bloodstream. Once the CSF has percolated through | | | | from the lumbar region is as good for diagnosis as |
| openings to get outside the brain, it is reabsorbed and | | | | from anywhere else, yet safer to obtain. |
| recycled into the bloodstream. The entire volume of | | | | Once the spinal needle enters the lumbar sac of fluid, |
| CSF--about 150 milliliters or five ounces--is made and | | | | correct positioning of the needle is confirmed by the |
| reabsorbed several times per day. | | | | emergence of clear, colorless drops of fluid from the |
| Dr. Quincke understood that analyzing the CSF's | | | | back of the needle. (When a similar procedure is |
| makeup could be useful in diagnosing infections and | | | | performed for the purpose of epidural anesthesia, the |
| other diseases affecting the central nervous system | | | | tip of the needle stops just short of entering the |
| (brain plus spinal cord). Measuring the CSF's protein | | | | meninges, and the drug is infused outside the sac.) A |
| and glucose (sugar) content along with inspecting a | | | | thin plastic tube is then attached to the back of the |
| sample of CSF under a microscope to count red and | | | | needle so the CSF's pressure can be measured. |
| white blood-corpuscles soon became standard | | | | Subsequently, CSF is allowed to drip into each of |
| practices. | | | | several sealable test-tubes suitable for sending to the |
| The premier use of lumbar puncture in both Quincke's | | | | laboratory. |
| time and ours has been to diagnose meningitis. The | | | | Once adequate fluid has been obtained, the needle is |
| suffix "-itis" signifies inflammation, so meningitis means | | | | withdrawn and the small puncture site in the skin is |
| inflammation of the meninges. Most, but not all, | | | | covered with an adhesive bandage. Typically, there |
| instances of meningitis are due to infections, but the | | | | are no more than a few drops of blood-loss from this |
| kinds of infections seen have evolved over the years. | | | | test. |
| In Quincke's lifetime tuberculosis and syphilis germs | | | | How about risks? Fortunately, they are minimal. As |
| were common causes of meningitis, but presently, in | | | | with any other test in which a needle is inserted |
| developed countries these are uncommon. Nowadays, | | | | somewhere that Mother Nature never intended, |
| the usual causes of meningitis are other bacteria, | | | | bleeding is a possibility. Luckily, there are no major |
| viruses or even funguses. In cases of suspected | | | | blood-vessels in the vicinity, so even an off-course |
| infection, CSF protein, glucose and blood-corpuscle | | | | needle is unlikely to cause trouble. Theoretically, a |
| measurements are supplemented by other tests on | | | | needle-insertion could also bring germs into the body |
| the fluid that can track down the specific, infecting | | | | and cause infection, but this almost never occurs |
| organisms. | | | | because the needle is sterile and because the lumbar |
| Another important use of lumbar puncture is to | | | | region had been surgically prepped. |
| diagnose subarachnoid hemorrhage, an abrupt, | | | | About one-in-five patients experiences a headache |
| devastating, and potentially lethal bleed into the CSF | | | | from the procedure. When a spinal-tap headache |
| space caused by rupture of an aneurysm or other | | | | occurs, it always has the following characteristics: it is |
| abnormal blood vessel. In suspected cases--classically | | | | present while the patient is sitting or standing, and is |
| presenting with "the worst headache of my life"--a | | | | promptly relieved by lying down. Spinal-tap headaches |
| computed tomographic (CT) scan is usually performed | | | | are due to persistent leaking of CSF through the hole |
| first. While very sensitive in detecting subarachnoid | | | | that the needle made in the meninges. (The leaking |
| hemorrhages, CT scans can still miss cases. So if the | | | | occurs within the spinal column and doesn't leave the |
| doctor is still suspicious that a bleed occurred, the next | | | | body.) Until the hole seals up again and the full volume |
| step is to do a lumbar puncture which is 100% sensitive | | | | of CSF is restored, the CSF cannot provide its usual |
| in detecting this condition. That is, it never misses. | | | | cushioning effect with changes in head position, and a |
| Lumbar puncture with CSF analysis can also help in | | | | headache ensues. In such cases the patient remains |
| the diagnosis of multiple sclerosis, a disease in which | | | | horizontal until the leak has sealed over. |
| the patient's own immune system attacks the central | | | | Reviewing a list of potential complications can have a |
| nervous system. In this condition the immune reaction | | | | discouraging effect on people who need a test. But it |
| produces abnormal proteins that can be detected and | | | | is reassuring to know that millions of people have had |
| measured in the CSF. | | | | Dr. Quincke's test since he devised it over a century |
| How is the test performed? Well, the first step, of | | | | ago. If the test caused unforeseen problems, they |
| course, is the informed consent process in which your | | | | should have turned up by now. |
| doctor explains the risks and benefits of the test and | | | | |