A short introduction to MULTIPLE SCLEROSIS - Page 2
A diagnosis of MS (Sibley 1990) is usually based on combination of:
- medical history and neurological examination
- evoked potential tests
- magnetic resonance imaging (MRI scan)
- laboratory analysis of cerebrospinal fluid, known as lumbar puncture (this procedure is less frequently used nowadays).
Symptoms-what they are, how long they have been present, how often they occur, and where they occur-as well as any other significant current or previous health problems, will be discussed at the initial consultation with the neurologist.
If MS is suspected, a basic neurological examination should reveal some abnormality. Some of the criteria routinely assessed include vision, gait, motor power, coordination, speech, reflexes, sensation and mental status (Sibley 1990). If vague, symptomatic complaints cannot be substantiated by objective evidence of neurological deficits, the case for a diagnosis of MS is considerably weakened (Herndon 1994; Rolak 1996).
Evoked potential tests
These use painless electrodes, placed on the scalp, to measure the speed at which electrical impulses travel along damaged nerves. Evoked potential tests can pinpoint specific central nervous system pathways affected by inflammation and demyelination. They can therefore indicate the need for MRI, to establish if there are other. "silent" lesions which are not producing symptoms.
There are three main variations of this test: visual evoked potential, which assesses impulse conduction through the optic nerve on visual stimulation, and is the most frequently used of the three; auditory evoked potential, which tracks impulses through the auditory nerve; and the somato-sensory evoked potential, which measures conduction through sensory pathways in response to stimulation of the skin (Rolak 1996; Holland et at 1996).
Magnetic resonance imaging, known as MRI, indicates areas of inflammation in the white matter of the central nervous system, and it has revolutionised the diagnosis of MS. However, it is not a definitive test. Brain lesions resembling those found in MS appear on the MRI brain scans of 10 per cent or more of healthy, middle-aged people (Triluzi & Scotti 1998). Conversely, some people with MS may have normal MRI brain scans. Positive MRI changes are nevertheless seen in about 95 per cent of people with definite MS (Rolak 1996). Spinal cord MRI, combined with brain MRI, can improve the accuracy of diagnosis in some people.
MRI may also be inconclusive in people with mild forms of MS, or in the early stages of the disease (McDonald 1998). Other diseases, including Lyme disease, human T cell lymphotropic virus infection, and systemic lupus erythematosus, can produce similar brain images: thorough clinical and laboratory assessment should eliminate these possibilities (Sibley 1990).
MRI has been used in clinical trials to follow disease progression and assess the effectiveness of new treatments.
However, scan results do not always reflect the level of clinical disability (Clanet and Berry 1998): a person can have many lesions, yet little disability, or severe disability, with few or no detectable lesions.