MS's New Challenge: The McDonald Criteria 2 of 4

 

 

In a Nutshell

 

The general conclusions of the new criteria are:

  • The diagnosis of MS requires objective evidence of lesions disseminated in time and space.
  • MRI may contribute to determining dissemination in time and/or space.
  • 3 diagnostic categories were established: possible MS, MS, or not MS.
  • Other supportive tests include CSF and VEP
  • The category of probable MS had little practical value for clinicians - and has had no value in clinical trial utilization; it has therefore been eliminated.

Importance of MRI

Although the McDonald criteria retain the time-honored (and well-established) basis for diagnosing MS by clinical means, MRI now plays a much larger role in our new diagnostic guidelines. Although the gold standard thus remains a complete neurologic history and detailed neurological examination providing evidence for more than one episode involving more than one area of the CNS - and no better diagnosis present - neuroimaging now may provide evidence of dissemination in the nervous system. 

If an MRI of the brain or spinal cord performed at three or more months after an initial clinical event demonstrates a new Gadolinium-enhancing lesion, this would indicate a new CNS inflammatory event. The duration of Gadolinium enhancement in MS is generally less than 6 weeks. If one does not see a new Gadolinium enhancing lesions but does see a new T2 lesion (presuming an MRI was done at the time of the initial event), then one should perform a repeat MRI scan after another three months. All events within the first 30 days after an exacerbation are considered part of the initial exacerbation; the new T2 lesion developing within the 30 days following an exacerbation would not count as a new event - the new lesions seen on the 3-month scan, however, would be a new a presumably separate demyelinating event. This is, of course, only a guideline given by the committee. Individual neurologists must make their own call on this information.

The McDonald criteria recognized the need for standardization of MR imaging; a consensus meeting organized by the Consortium of MS Centers issued recommendations regarding the requirements fro MRI. These include contiguous slices with a thickness of 3mm, standard T1, T2 and FLAIR and T1 Gadolinium enhanced sequences in at least two planes (coupled with a adequate field strength - 1.5 Tesla).

Table 2. New diagnostic criteria for MRI determination of dissemination in time

  • Gadolinium enhancing lesion demonstrated in a scan done at least 3 months following onset of a clinical attack at a site different from attack, or
  • In the absence of Gadolinium enhancing lesions at the 3 month scan; follow up scan after an additional 3 months showing a Gadolinium enhancing lesion or new T2 lesion.