Continued from page 1
The next step is to lie on your side on a bed or procedure table with your knees tucked up to your chest. The skin of your lower back is painted with an iodine-based solution to produce a sterile field. If you have an allergy to iodine, an alcohol-based solution is substituted. The surrounding area is then covered with sterile paper or cloth. The skin and
tissue beneath
skin are then numbed with local anesthetic, and then everything is ready to insert
spinal needle.
The reason
lower back (lumbar spine) is chosen is because here
sac of meninges can be entered without risk of poking a hole in
spinal cord. This is because
spinal cord ends several inches higher within
spinal canal. The composition of
CSF is nearly
same throughout its system. Thus, CSF from
lumbar region is as good for diagnosis as from anywhere else, yet safer to obtain.
Once
spinal needle enters
lumbar sac of fluid, correct positioning of
needle is confirmed by
emergence of clear, colorless drops of fluid from
back of
needle. (When a similar procedure is performed for
purpose of epidural anesthesia,
tip of
needle stops just short of entering
meninges, and
drug is infused outside
sac.) A thin plastic tube is then attached to
back of
needle so
CSF's pressure can be measured. Subsequently, CSF is allowed to drip into each of several sealable test-tubes suitable for sending to
laboratory.
Once adequate fluid has been obtained,
needle is withdrawn and
small puncture site in
skin is covered with an adhesive bandage. Typically, there are no more than a few drops of blood-loss from this test.
How about risks? Fortunately, they are minimal. As with any other test in which a needle is inserted somewhere that Mother Nature never intended, bleeding is a possibility. Luckily, there are no major blood-vessels in
vicinity, so even an off-course needle is unlikely to cause trouble. Theoretically, a needle-insertion could also bring germs into
body and cause infection, but this almost never occurs because
needle is sterile and because
lumbar region had been surgically prepped.
About one-in-five patients experiences a headache from
procedure. When a spinal-tap headache occurs, it always has
following characteristics: it is present while
patient is sitting or standing, and is promptly relieved by lying down. Spinal-tap headaches are due to persistent leaking of CSF through
hole that
needle made in
meninges. (The leaking occurs within
spinal column and doesn't leave
body.) Until
hole seals up again and
full volume of CSF is restored,
CSF cannot provide its usual cushioning effect with changes in head position, and a headache ensues. In such cases
patient remains horizontal until
leak has sealed over.
Reviewing a list of potential complications can have a discouraging effect on people who need a test. But it is reassuring to know that millions of people have had Dr. Quincke's test since he devised it over a century ago. If
test caused unforeseen problems, they should have turned up by now.
(C) 2005 by Gary Cordingley

Gary Cordingley, MD, PhD, is a clinical neurologist, teacher and researcher who works in Athens, Ohio. For more health-related articles, see his website at: http://www.cordingleyneurology.com