I agree with @Woolie that there are lots of problems with drawing conclusions from this study. MS is defined as multiple episodes of neurological deficit differing in time and site of involvement. That means that in the ideal situation everyone sent with a diagnosis of MS to a specialist centre does not officially have it. Because ideally they will be sent with their first attack. And the 18% figure is likely to be an artefact of the particular referral dynamics locally. Elsewhere it might be more or less. I doubt it tells us anything very useful.