Neurologists have long recognized optic neuritis (or retrobulbar neuritis) to be a forerunner of MS in the majority of cases. Recognizing this and the fact that other problems such as transverse myelitis and acute symptoms of brainstem origin also usually end up diagnosed as MS, the McDonald committee has modified the Poser criteria to establish the “McDonald criteria.”
These criteria embrace the rational use of laboratory investigation in making the diagnosis of MS and but have abandoned the terms clinically probable and lab-oratory supported. The committee has simply and clearly outlined MRI criteria that can be used together with a history of a single clinical attack (called clinically isolated syndrome [CIS]) to make a diagnosis of MS with a high degree of certainty.
Approximately one in five or six persons diagnosed with MS based on MRI criteria will not have MS, however. In all probability, most of this small group will have had an attack of acute disseminated encephalomyelitis (a one-time “MS” attack). Recent evidence indicates that this kind of attack seems to be related to a different kind of immune reaction. We anticipate that new tests may help to distinguish this group at the onset of illness.
The decision of the committee to include MRI criteria for a CIS and to equate CIS with a diagnosis of MS was, in part, driven by the evidence from two separate studies. These are the CHAMPS study of Avonex and the ETOMS study of Rebif. These studies showed superior results when interferon-beta-1a treatment was started after the very first clinical attack of MS. The very low dose of Rebif in the ETOMS study yielded inferior results as compared with the CHAMPS study. The FDA has accepted initiation of treatment based on the McDonald criteria, including the “CIS” category.