from the book, "Multiple Sclerosis" The Questions, The Answers", edited by Rosalind C. Kalb., Ph.D
There is another post here from this same book, where the discussion is on the signs and symptoms of someone who might have MS (signs are those things that the physician can test for, and get the same results on a repeated test; symptoms are those things that a patient reports -- like, numbness, tingling, problems walking, fatigue, etc.)
This post picks up where that one left off: The patient has come to the neuro and reported various symptoms; the doctor does his clinical testing, sends the person off for MRIs, blood tests, and maybe a spinal tap. After all the testing is done, and the results are in, (and now, quoting from the book):
"In order to make a definite diagnosis of MS, the physician must find the following:
*plaques or lesions in at least two distinct areas of the Central Nervous System white matter;
*evidence that the plaques have occurred at different points in time; and perhaps most importantly
*that these plaques in the white matter have no other reasonable explanation.
In other words, MS is a diagnosis that can be made only after every other possible explanation of the signs and symptoms has been ruled out."
and a bit later,
"For some people, no tests beyond (the patient's history) and neurological exam are necessary to make the diagnosis. If the doctor is able to find evidence of multiple lesions in the Central Nervous System that have occurred at different points in time
and have no other reasonable explanation, the diagnosis can be made without any other testing being done. However most physicians will not rely entirely on this type of evaluation and will do at least one other test to confirm the diagnosis."
Here are some of the tests commonly used: MRI of the brain, which is abnormal in about 90% of people with definitive MS. The MRI of the spine -- which is not as frequently positive as MRI of the brain.
Some doctors use the CAT scan, but this has pretty much been replaced with the MRI.
Visual evoked potential (VEP) and the somatosensory evoked potential (SSEP). These tests, which look at the speed and efficiency of myelin conduction, are frequently abnormal in definite MS. VEP's have a 90% rate, SSEP not quite as high.
Lumbar Puncture, or spinal tap, where the doctor is looking for 1) elevations in immunoglobulin G (IgG), a protein which is indicative of some abnormality in the immune system; and 2) the presence of a specific IgG that appears in the flue as oligoclonal bands.
Neither of these is specific to MS, making a lumbar puncture primarly useful for confirming the diagnosis of MS when there is other suggestive evidence.
So a patient goes in with symptoms, the doctor finds signs, does testing (along with these tests, often a bunch of blood tests), and then lays out all the evidence. Think of it as "circumstantial evidence", as there is no direct evidence that is specific to MS. He lays out the evidence, and if there is enough of it to point to MS, then he'll likely diagnosis it as MS.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....