The term Spinal Tap has always had a negative association. Patients shudder when they hear a doctor say, ”you need to have a spinal tap.” Oh, no, not that! Its The Godfather of all tests—worst of the worst! Do you really have to, Doc? Do you?”
In the 80’s, Rob Reiner wrote and directed a movie titled “This is Spinal Tap” about a fictitious British rock band, who played louder than anyone could stand, and was composed of obnoxious, oddballs. The band’s name was “Spinal Tap”—the negative association lives on.
Actually, a spinal tap, correctly called a lumbar puncture (LP), isn’t the worst of all the tests man can inflict upon his fellow man! Needle biopsies of the bone marrow, liver, kidneys, and lungs are far more dangerous and uncomfortable than spinal taps. It’s just the idea of having a big needle put in your back that upsets people. The unfounded fear of spinal cord damage and paralysis has caused more than a few people to refuse the test. I’ve never seen or heard of that happening because the spinal cord ends 5 inches above the puncture site.
The lumbar puncture is a test that’s done far too infrequently. A professor once told me, during the evaluation of a patient, if you think about doing it, you should. A doctor never regrets doing one. It is a “diagnostic tool for conditions of the central nervous system” particularly helpful when you suspect infection or brain hemorrhage. The information obtained from a spinal tap is helpful, even if it’s negative.
Why do doctors do a spinal tap? Because it’s the easiest way to obtain a sample of cerebrospinal fluid (CSF), needed to diagnose brain and spinal cord diseases. The brain and spinal cord are covered by a thick membrane, the Dura Mater. The Dura lines the inner surface of the closed, bony space that confines the brain and spinal cord. CSF is a clear, watery substance found flowing between the Dura and the brain. It bathes the entire brain and spinal cord. It is produced inside the brain by specialized cells called the Choroid Plexus located in a network of cavities (open spaces) called Ventricles. CSF circulates around the brain and spinal cord and is renewed 4 times every 24 hours. It cushions and protects the brain while also contributing to growth and regeneration of brain cells.
Sampling and analyzing CSF is useful for diagnosing diseases of the central nervous system, such as meningitis, encephalitis, and subarachnoid hemorrhage. Bacterial and viral infections are the most common, but parasitic and fungal infections also occur in the central nervous system. Imaging studies such as Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) have had a big impact on the performance of spinal taps. Doctors have relied too heavily on the results of imaging studies and forgotten to do spinal taps when they should be done. CT and MRI are sensitive tests but not for diagnosing everything.
During a spinal tap, spinal fluid is withdrawn from a space at the lower end of the spinal canal called the lumbar cistern. The patient lies on his side in the knee-chest position. Then a sizable needle is passed between two lower vertebrae into the cistern. The skin is anesthetized first and blood is drawn to patch the needle puncture site in the Dura after the tap. This “blood patch” seals the puncture site to prevent a CSF leak. Cerebrospinal fluid is collected in sterile, sealable glass tubes and sent to the lab for analysis.
CSF is tested for several items (parameters) which are the following:
Color: Clear—normal
Cloudy—possible infection
Xanthochromia—amber/yellow color from broken-down red blood cells
Pressure:
Opening—high or low—indication of over-production of CSF, blockage of normal
flow, or a sign of a CSF leak.
Closing
Cell count:
Red blood cells—indication of hemorrhage
White blood cells, and type—indication of infection
Protein—elevated in many diseases
Glucose—elevated in meningitis, hemorrhage
Gram stain—tests for presence of bacteria
Fungi—special stains used
Culture—test for identification of bacteria type
Specialized Tests—done when certain conditions are suspected
This is probably too much “Doctor-speak,” but these tests all have an important purpose. My favorite neurologist of all time, Dr. Bill Fulton, did spinal taps on nearly every patient he saw. He didn’t do them for money or to get more practice (he didn’t need that). He did them because he always felt testing the spinal fluid gave him an immense amount of information. He did an India Ink stain test on nearly every specimen. India Ink stain detects a rare fungal infection of the brain called Cryptococcosis. It causes severe, often fatal meningitis which can be mis-diagnosed as dementia. Before the days of routine CT scanning, I saw an elderly lady in the ER with the recent onset of fever, headache, and confusion. I did a lumbar puncture (LP) and sent the fluid for analysis including an India Ink stain.
I still vividly remember the shock I felt when the lab called to tell me her CSF was abnormal and her India Ink test was positive—she had Cryptococcosis! She was transferred to ICU, started on IV anti-fungal drugs, and referred to Dr. Fulton. Unfortunately, she succumbed to the disease. Had I not done a spinal tap or India Ink test, she probably would still have died, but knowing her actual diagnosis, allowed us to start the correct treatment early. That was her only chance to survive.
Dr. G’s Opinion: If I felt a spinal tap was indicated, I never hesitated to do one. The parents of babies were the hardest to convince, but babies and toddlers were the easiest to do LP’s on. If my helper held the child still, I could get spinal fluid in just a few seconds. The results were the bad part because abnormal CSF meant the child had a serious illness and could die. I did LP’s in the office, in the ER, in Hospital beds, and pediatric treatment rooms. The difficulty and danger of a spinal tap is a cultural myth. In a cooperative, still, un-wiggly person it’s an easy procedure.
Today’s doctors rely too heavily on CT and MRI and neglect the most definitive test. It takes time and patience to explain the procedure, convince the patient to have it, and get it set up to perform. Many doctors are too impatient to bother and omit the test that gives them a wealth of information. As I said before, CT and MRI can’t diagnose everything. Doing an LP supplements those studies, and may in fact, provide more helpful information. Remove from your mind fear of paralysis or spinal cord or nerve injury. Those things don’t happen. Knowing what a patient’s spinal fluid is like is more valuable in diagnosing central nervous system disorders than just about anything else.
Reference: Shahan B, Choi EY, Nieves G. Cerebrospinal Fluid Analysis Amer Fam Phys 2021 April 1;103(7):422-429.
Sakka L, Coll G, Chazal J. Anatomy and Physiology of cerebrospinal fluid. Eur Ann Otorhinolaryngology 2011;128:309-316.
