The McDonald Criteria for Multiple Sclerosis: time for clarification.

The McDonald Criteria for Multiple Sclerosis in general have replaced the Poser criteria. Despite this, many consider that there are still areas of ambiguity. In this study, neurologists completed a questionnaire about familiarity with, usefulness and applicability of the McDonald Criteria for Multiple Sclerosis. Understanding of 'attack'; objective clinical evidence; 'two or more lesions' and their ability to interpret case scenarios was evaluated. Responses were analysed overall and by skill group. Ninety-seven consultants and 30 trainees responded, of whom 37 operated a multiple sclerosis clinic ('experts'). Some (62%) thought the McDonald Criteria for Multiple Sclerosis were useful, and 31% found them confusing or difficult to apply; 38% thought the criteria should be applied universally, others (14-28%) favoured their use for drug trials/research, and 17% rarely used them. Thirty-six (29.1%) thought the McDonald Criteria for Multiple Sclerosis specified two categories: 'MS and not MS', but others considered 'possible' or 'probable' multiple sclerosis were permitted. Experts understood better 'an attack' and 'objective clinical evidence'. All skill groups comprehended poorly what constituted an episode of demyelination, and whether Lhermitte's phenomenon was acceptable as evidence for cervical cord demyelination. A consistent response was given by 44-50% to 'two or more lesions', although this is not well defined. Criteria for primary progressive multiple sclerosis were understood well. We conclude that the McDonald Criteria for Multiple Sclerosis have improved diagnosis but areas of misinterpretation remain, particularly the definition of 'an attack', 'objective clinical evidence' and 'two or more lesions'. There was uncertainty about how many multiple sclerosis categories were permitted and whether the terms 'possible' and 'probable' were allowable. Further clarification might allow the criteria to be applied more consistently.