Multiple sclerosis (MS) is difficult to diagnose for two reasons. First, MS symptoms may come and go over a period of years, and can resemble several other illnesses. Second, there is no single specific diagnostic test for MS. Diagnosis is based upon the patient's history combined with the results of a neurological evaluation, diagnostic tests, and any symptoms present at the time of the evaluation.

Before a definite diagnosis can be made, other conditions must be ruled out. MS symptoms can resemble those caused by stroke, brain infection, vitamin deficiency, vascular inflammation, or even migraine headaches. Because so many conditions can mimic MS, diagnostic tests are often used to finalize a diagnosis. However, normal test results are possible even when a person actually has MS. For this reason, it is important to find a neurologist who has experience with MS. Experienced doctors can be found at any of the 140 Consortium of MS Centers in the United States and Canada.

These are the procedures used to help diagnose MS:

Diagnosis begins with a neurological history and an examination. The history should suggest acute attacks or slow worsening. The purpose of the examination is to detect abnormalities in the central nervous system. The neurologist will assess each area of the patient's basic function: cranial nerve function, motor skills, sensory capacity, mental status, coordination, and reflexes. He or she will observe the patient's balance, eye movements, gait, posture, speech and coordination. The doctor may ask questions to assess memory, judgment and clarity of thought.

The MRI is a non-invasive test that is completely painless but rather noisy. In this procedure, which lasts between 30 and 90 minutes, patients are scanned in a tunnel-like structure that uses radio waves, magnetism, and a computer to produce detailed images of body structures. To help diagnosis MS, a specialist uses the MRI to measure lesions (scar tissue also known as "plaques") in the brain. The MRI can detect brain lesions better than a CT scan: It reveals their size, quantity, and distribution. When a chemical compound, gadolinium, is administered during the MRI, the test can even distinguish between new active lesions and older inactive ones. The images generated by the scan are read on computer screens. In people with MS, the MRI results are generally abnormal. Most people (95 percent) who have had MS for three years have lesions that show up during the brain scan. The remaining 5 percent probably have spinal cord lesions or lesions that cannot be detected with MRI. Sometimes a MRI of the spinal cord is also done.

When the neurological exam and MRI are inconclusive, other tests are used to help diagnose or rule out MS. These include:

Evoked Potential Tests. There are three tests that measure the speed of electrical impulses carried by the nerves. Because the rate of conduction is much slower through demyelinated nerve fibers, these tests are helpful in diagnosing MS. It usually takes about two hours to administer all three tests.

Visual Evoked Potential Test (VEP). This test measures the time it takes for nerve impulses to travel from the retina of the eye to the occipital lobe of the brain. VEP is a painless test that involves watching lights or patterns flash across a screen. The visual stimulation creates electrical impulses that travel to the brain. The impulses are tracked and recorded with electrodes on the scalp. Most patients with definite MS (up to 80-90 percent) have abnormal conduction rates, as do 58 percent of those with probable MS. Recent studies have shown that people whose VEP is abnormal are 2.5 to 9 times more likely to develop clinically definite MS than people with normal VEPs.

Auditory Evoked Potential Test (AEP). The AEP measures the time it takes for nerve impulses to travel from the ear to the brain. This test can detect lesions in the auditory pathways of the brain stem. This painless test involves listening to a series of clicks and tones. Electrodes on the ear lobe and the scalp record the speed of the nerve impulses created by the sounds. The test is done on both ears. Abnormal responses are found in up to 40 percent of those with probable MS and in up to 67 percent of those with definite MS.

Somatosensory Evoked Responses (SER). This slightly uncomfortable test takes about a half-hour. A small amount of current is made to travel from electrodes on the scalp, wrists and knees to the cortex of the brain. The SER measures and records the time this takes. SER abnormalities are present in up to 77 percent of those with definite MS and in up to 67 percent of those with probable MS.

Lumbar Puncture or Spinal Tap. An analysis of cerebrospinal fluid can help with the diagnosis of MS. After the patient receives local anesthetic, cerebrospinal fluid is obtained by inserting a very thin needle into the spinal canal and withdrawing small amounts of fluid. This clear, colorless fluid is evaluated for two major immunological abnormalities: the presence of immunoglobulin oligoclonal bands and intrathecal immunoglobulin (intra CNS) IgG production. Oligoclonal bands are ultimately found in 90-95 percent of patients with MS. The bands indicate an immune response in the central nervous system. Other diseases can cause oligoclonal bands, so their presence is not a definite indicator of MS. Increased intrathecal IgG synthesis is ultimately found in 70-90 percent of MS patients.

Blood Tests. Blood tests are used to rule out other conditions with symptoms similar to MS, including Lyme disease, AIDS, and certain genetic disorders.

A definite diagnosis of MS can be given if these criteria are met: 1. The disease has followed a consistent course. The relapsing-remitting course will have had at least two bouts separated by at least a month; the progressive course will have shown slow or stepwise progress for at least 6 months.

2. There are documented neurologic abnormalities in more than one site in the brain or spinal cord white matter. If there is history or evidence in examination of only one lesion, an additional lesion must be evident on the basis of evoked responses or MRI. Spinal fluid abnormalities (oligoclonal bands or intrathecal IgG production) make the diagnosis more likely.

3. The onset of symptoms was between the ages of 10 and 50.

4. There is no other more likely neurological explanation for the patient's symptoms and test results.

References

First published October 1, 1999
Last updated May 2, 2003
Copyright © 1999 Accordant Health Services, Inc. All Rights Reserved.

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