My friend, MyMsBs provided me some information to some questions I asked him on diagnosing MS. He provided me a very thoughtful and detailed response that I thought I would share with everyone who ever wondered about how doctors go about getting to a dx. Here it is, with his permission to publish:

Hey Ichy!
CSF is just an abbreviation for Cerebrospinal fluid. CSF surrounds your spinal cord and your brain. It provides cushion and buoyancy by allowing the brain to actually "float" in it, thereby greatly reducing the mass of the brain resting inside the cranial cavity. The brain, contrary to popular belief, doesn't occupy the entire area inside the cranium, and CFS fills the gap and helps provide a "shock absorber" like property.

Now on to the McDonald Criteria. Look at the first line: Clinical Presentation. It states that two things be present, "2 or more attacks (relapses), 2 or more objective clinical lesions." The second part of the first line is for "Additional Data Needed": "None; clinical evidence will suffice (additional evidence desirable but must be consistent with MS)"

So, by the first line of the McDonald Criteria to be used for a Dx of MS, an MRI or Spinal Tap aren't even mentioned. So... what do they mean then by "2 or more objective clinical lesions" if you can't look at them?? Confusing right? Not at all. On a complete and thorough physical neurological exam, findings such as a Babinski Reflex, Hoffman's Sign, marked paresis or paralysis of a limb, hyperreflexia etc. all point the neurologist in the right direction to determine where the lesion causing these abnormalities to exist is located in the brain or spinal cord. By this comprehensive neurological exam, a well qualified neuro experienced in MS can tell you almost exactly where a lesion MUST be present to produce such an abnormality.

The Qualified MS Neuro then proceeds to "Rule Out" or exclude all of the other possible causes potentially responsible for these findings. If all of those additional tests are negative for other pathology, you then can conclude a Definitive Diagnosis of MS... "2 or more objective clinical lesions" determined to exist by physical exam, with all other causes for them eliminated. That along with a lengthy enough patient history to show that the events are occuring in different places in the body and seperated by different amounts of time, are all that is necessary to render a positive dx of MS.

Most "general" neurologists and PCP's simply want to see a positive MRI or abnormal CSF in a lumbar puncture to make a dx of MS. While this is not the appropriate way to Dx MS, it can also yield a "False Positive" Dx of MS, and totally miss the true underlying cause of the signs and symptoms of the patient. Anytime I hear of someone who went to, let's say an eye doc, that saw evidence of previous ON, they were sent for an MRI , it came back positive, and they were Dx'd a week later with MS, and after 5 years have seen their neuro 3-4 times total since then, I am automatically skeptical about the accuracy of their dx.

What people MUST remember, is that there is NO pathognomonic test for MS. In other words, spots on an MRI and O-bands in the CSF are highly "suggestive" of MS, but by themselves CANNOT conclude an accurate Dx of MS. Many MS lesions are simply too small to be seen by the human eye, and often can only be found under microscopic exam during a postmortem exam of the brain and spinal cord with a microscope. That being the case, do you think that a lesion (or a multitude of them) 1/100th or even 1/1000th of a mm (although large enough to cause multiple clinical findings) can be seen on an x-ray type film, on which the images aren't even the actual size of the brain or spinal cord, by the human eye? No, they can't.

Here is a good read (link below) I ran across that explains much more about missed dx's and false positive and negative dx's determined only by looking at simple tests, rather than analyzing the patients entire clinical picture, and documenting a detailed history of events or the course of the disease. The neurological history of an MS patient along with physical findings on exam that the neuro can actually illicit and are reproducible, carry far more weight in the diagnostic arena than any spots on an x-ray type film ever will.

Until there is a definitive pathognomonic test that is proven to be positive ONLY for MS (which will require the cause of MS be determined before such a test can exist), the diagnosis of MS will remain a time consuming process of diagnosis by exclusion. In other words, you have to prove that no other disease process is causing the signs/symptoms, and that because all of the signs/symptoms point to MS, it therefore must be MS.

Here is the link to read I suggested:
http://www.medhelp.org/tags/health_page/7687/Multiple-Sclerosis/How-Can-a-Person-with-MS-Have-a-Negative-MRI?hp_id=161

Hope that answers some questions for you!! Feel free to republish this if you think anyone else will benefit from it.

Matz ; }-~

On a follow up to my previous response, I became curious about nerve sizes and did some research. I found that thinly myelinated A-delta fiber nerves, the ones that carry sensations of touch, pain, pressure and temperature often range between 1-5 micrometers, or 1-5/1000ths of an inch in diameter. A standard sheet of copier paper is about 3/1000ths of an inch. As you can surmise by this comparison, spotting a demyelinated area a few thousandths of an inch thick on a reduced size image, with only the human eye, can be comfortably listed as "near impossible".