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Diagnosis: The Basic Facts
MS is a disease of the central nervous system. The central nervous system consists of the brain, spinal cord, and the optic nerves. Surrounding and protecting the nerve fibers (or axons) of the central nervous system is a fatty tissue called myelin, which helps nerve fibers conduct electrical impulses.
In MS, myelin is lost in multiple areas, leaving scar tissue called sclerosis. These damaged areas are also known as plaques or lesions. Sometimes the underlying nerve fiber (or axon) is also damaged or broken.
When myelin or the nerve fiber is destroyed or damaged, the ability of the nerves to conduct electrical impulses to and from the brain is disrupted, and this produces the various symptoms of MS.
MS is not contagious. No one can catch MS from another person.
What Causes MS?
Scientists do not yet know what might cause the immune system to do this. Most agree that several factors are involved, including something in the person's genetic make-up coupled with exposure to something in the outside world, possibly exposure to a common virus or bacterium.
How Is MS Detected?
A physician often requires all three in order to rule out other possible causes for symptoms and to gather facts consistent with a diagnosis of MS.
MS symptoms can include reduced or abnormal sensations, weakness, vision changes, clumsiness, sudden loss of bladder control, and so on. Symptoms might appear in any combination and be mild or severe. They are usually experienced for unpredictable periods of time.
But symptoms alone don't indicate MS. Any one or combination of these symptoms might have causes unrelated to MS.
Signs are indications of the disease that are objectively determined by a physician. Some signs might even explain a person's symptoms, but others have no corresponding symptom.
Common signs that can be detected by the doctor during a physical examination include:
The physical examination may consist of the following:
Magnetic Resonance Imaging
Laboratory tests may be the crucial element of the diagnosis process. The preferred test, which detects plaques or scarring possibly caused by MS, is magnetic resonance imaging (MRI).
The MRI scan is a diagnostic tool that currently offers the most sensitive non-invasive way of imaging the brain.
Unlike Computerized Tomography (CT) or conventional X-ray, the MRI scan does not use radiation. Instead, it uses magnetism and radio waves. Powerful magnetic fields interact with the hydrogen atoms found in the water contained in all body tissues and fluids. Radio frequency signals cause these hydrogen atoms to release energy, and computers translate the changes into cross-sectional images.
The scanning procedure is very sensitive, and can often create pictures of lesions, or areas of damage, that would be missed by a CT scan.
Although the absence of radiation is an asset, the powerful magnetic field of MRI means that it can't be used by people who have cardiac pacemakers or metal implants, such as aneurysm clips, in their bodies. Dental fillings cause no problem.
An abnormal MRI does not necessarily mean MS. There are other diseases that cause lesions in the brain that look like those caused by MS. There are also spots found in healthy individuals, particularly in older persons, which are not related to any ongoing disease process. These are often called UBOs, for unidentified bright objects.
On the other hand, a normal MRI does not absolutely rule out MS. About 5% of people who are confirmed to have MS on the basis of other criteria, do not show any lesions in the brain on MRI. These people may have lesions in the spinal cord or may have lesions that cannot be detected by MRI.
A clear-cut diagnosis might be made based on an evaluation of symptoms, signs, and the results of an MRI, but additional tests may be ordered as well. These include tests of evoked potential, cerebrospinal fluid, and blood.
Evoked potential (EP) tests are electrical diagnostic studies that can show if there is a slowing of messages in various parts of the brain. They often provide evidence of scarring along nerve pathways not apparent any other way.
The EP test most widely accepted as an aid to an MS diagnosis is the Visual Evoked Potential (VEP). The person sits before a screen on which an alternating checkerboard pattern is displayed.
The results are interpreted by a neurologist or neurophysiologist who has special training in this test.
Cerebrospinal fluid, sampled by a lumbar puncture (also called a spinal tap), is tested for levels of certain immune system proteins and for the presence of a staining pattern of antibodies called oligoclonal bands. These bands indicate an immune response within the central nervous system. Oligoclonal bands are found in the spinal fluid of 90-95% of people with MS. However, they are present in other diseases as well, so oligoclonal bands alone cannot be relied on as positive proof of MS.
While there is no definitive blood test for MS, blood tests can positively rule out other causes for various neurologic symptoms, such as Lyme disease, a group of diseases known as "collagen-vascular diseases", certain rare hereditary disorders, and AIDS.
The Diagnosis of MS
Until "1" and "2" have been satisfied, a physician will not be able to make a definite diagnosis of MS. Waiting in limbo is extremely trying. Receiving an incorrect diagnosis may be even worse. Depending on the clinical problems present when a person sees a physician, one or more of the tests described above might be done. Sometimes tests are done several times over a period of months to help gather needed information. A definite MS diagnosis satisfies the McDonald criteria, named for the distinguished neurologist W. Ian McDonald who sparked Society-supported efforts to make the diagnostic process for MS faster and more precise. The McDonald criteria were revised in 2005 to incorporate new data that should speed the diagnosis without compromising accuracy.
Before Definite Diagnosis
The National MS Society does not require people to have a definite diagnosis before offering support, information, and services. Chapters of the National MS Society can also provide referrals to area physicians who have experience diagnosing and treating MS.
A Word on Referral
1. "International Panel Revises Diagnostic Criteria for MS", Research/Clinical Update, Nov 10, 2005. © 2005 National MS Society.
3. " Living with MS," by Debra Frankel, MS, OTR with Hettie Jones © 2005 National MS Society.
4. "Multiple Sclerosis: The Questions You Have-The Answers You Need," by Rosalind C. Kalb, PhD, Third Edition. © 2004 Demos Medical Publishing. (www.demosmedpub.com).
For additional information
|Last updated August 8, 2006|