Magnetic resonance imaging (MRI) has been shown in a number of studies to be a very sensitive method for detecting focal areas of damage in the white matter of the cerebral hemispheres. This sensitivity has been reflected in the wave of enthusiasm with which MRI has been used in the diagnostic evaluation of suspected multiple sclerosis (MS). MRI cannot, at this time, distinguish between various tissue characteristics such as edema, infarction, inflammation, or demyelination. The detection of a discrete white matter lesion that has a strong signal on spin echo (SE) or a weak signal on inversion recovery (IR) has no specificity for MS or demyelination but can be used as evidence of neurological abnormality just as can nystagmus or a Babinski sign.
As is the case with evoked potentials, the main value of MRI in the diagnosis of MS lies in demonstrating lesions that are not clinically detectable in order to satisfy the criterion of dissemination in space. The degree to which patterns of one, two, three, or several discrete white matter lesions are specific for MS is not yet known. Systematic studies have shown that MRI is positive in 70-95% of patients with clinically definite MS (CDMS). In cases of suspected MS, MRI is positive (to some degree) in approximately 50% of cases. Follow-up studies, not yet completed, will tell just how accurately a positive MRI study will predict a diagnosis of CDMS.
It is therefore proposed that MFU studies suggestive of MS be treated as follows: