Understanding Results of the Spinal Tap

QUESTION: We have had a terrible anxiety provoking experience, as our
daughter was admitted to the hospital with meningitis. The doctors were
patient and caring, but when they explained all about the results of the
spinal tap, we were really too upset to understand. Can you tell us what was
meant by talk of cells, pressure and all the rest? Our daughter is fine now
and we are calm enough to listen.
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ANSWER: Even in the best of circumstances, and that certainly does not apply
to the events surrounding a hospital admission, understanding all the
implications of a Lumbar Puncture (spinal tap) is not easy. But the results
that the physician can obtain from this procedure are critical, as it provides
an initial evaluation and diagnosis that not merely helps to establish the
diagnosis of meningitis, but may often identify the condition that is causing
the meningitis. The meninges are the tissues that cover and surround the
brain, and any irritation of these delicate structures produce the symptoms of
meningitis. Headache is the outstanding symptom, as well as fever, nausea,
irritability and confusion, all depending upon the severity and cause of the
inflammation. Since bacterial infection is life threatening, the physician
needs diagnostic information rapidly, and the spinal tap provides five
important bits of data that are extremely useful. They are pressure, number
of cells found, type of cells found, glucose in the spinal fluid, and protein
in the spinal fluid. For example, the pressure of the fluid in the spinal
column is normally about 100-200 mm, but may be increased or decreased
depending upon circumstances. In bacterial meningitis it is elevated.
Normally there are very few cells present, but that number may rise to as many
as 5000 per cubic mm in bacterial infections, yet stay below 700 when a virus
is the infecting agent. The types of cells found also aid the diagnosis, as
lymphocytes are most commonly found in most types of meningitis, while the
bacteria fighting white blood cells (polymorphonuclear leukocytes, to be
exact) are present in bacterial infections. Checking the amount of glucose
and protein in the fluid also help make the diagnosis as they, too, are
altered in different ways with different causes. While additional tests are
available to the physician, they may take precious time to perform, with
results available only after some period of waiting. Since choosing an
appropriate antibiotic and starting medication as soon as possible is the best
way to attack and overcome bacterial meningitis, the spinal tap is truly an
important first test. Not all the symptoms associated with bacterial
meningitis or viral meningitis are caused by these infections. Tumors, lead
toxicity, and even a condition (meningismus) that mimics the symptoms of signs
of meningitis without an infection, can create a diagnostic dilemma for the
physician, and it takes a careful workup to fully explore all the
possibilities. I am glad your daughter did well.