MS's New Challenge: The McDonald Criteria 3 of 4
Cerebrospinal Fluid; is it useful?
Spinal fluid immunologic markers were not felt by the international committee to be necessary for the diagnosis of relapsing forms of MS. However, CSF analysis was deemed necessary for diagnosing primary progressive MS (PPMS). PPMS is often difficult to diagnosis with this conditions' paucity of identifiable abnormalities on brain MRI. With respect to CSF testing, the presence of oligoclonal IgG bands in the CSF not present in serum - or an elevated IgG index - is considered to be supportive of a diagnosis of MS. In the presence of CSF Ig abnormalities by isoelectric focusing method, the MRI criteria for dissemination in space are relaxed, requiring only two MS lesions.
The international committee also considered that visual evoked potential responses provide diagnostically valuable data of dissemination of lesions in space - other evoked potentials do not.
The American Academy of Neurology Quality Standards Subcommittee practice parameter guidelines were taken into consideration when establishing the recommendations noted above.
How does this work in Practice?
How does one use these guidelines in a clinical neurology practice? The following guidelines are outlined in the McDonald criteria:
If a patient has had two or more attacks with objective evidence of involvement of two or more areas of the CNS, and there is no better diagnosis, then the criteria for MS has been established. This becomes important in regions where access to neuroimaging is limited. Obviously, if neuroimaging or CSF is also assessed, the findings should be consistent with the diagnosis of MS.
If your patient has had one attack and evidence of two lesions in the CNS, then the clinician will need to obtain evidence for dissemination in time - this can then be accomplished by either noting a second clinical event or a change on subsequent MRI.
If your patient has had two or more attacks but evidence on exam of involvement of only one area of the CNS, confirmation of dissemination in space must be established. A second attack, involving a new area of the CNS, or changes on subsequent MRI scans will fulfill this criterion.
When patients have had one attack and evidence of only one area of CNS involvement (optic neuritis, for example), dissemination in both space and time must be confirmed clinically or by fulfilling the MRI criteria for dissemination for each.
In primary progressive MS, the risk of confounding diagnoses is greater than for other forms of MS. For this reason, in the case of insidious onset and progression of neurologic dysfunction suggestive of MS, one needs to find positive CSF and evidence of dissemination in time by MRI or continued progression for at lease one year and dissemination in space by MRI or two or more spinal MRI abnormalities or four to eight cerebral MRI lesions and one spinal cord lesion or an abnormal VEP and four to eight cerebral lesions on MRI or an abnormal VEP and fewer than four cerebral lesions plus one spinal cord lesion. This requires a considerable amount of work on the part of the clinician, but fortunately, PPMS is a rarely seen diagnosis.
A careful review of the McDonald criteria, along with posting the elements of the new component aspects of the criteria in a place that the clinician can easily refer to it, will help considerably in clarifying what has been a confusing arena; the result of coupling new technology with a clinically based diagnostic skills.