FWIW it's not technically MS until there's been more than one incident, thus "multiple" in the name. The resultant lesions are usually visible on an MRI. Most people who have one incident to not go on to have multiple.

There's no definitive test other than this: multiple incidents of otherwise-unexplained neural compromise, verified by MRI as lesions on the myelin sheath. MS symptoms are readily addresses by steroids, unlike other similar conditions, so that can also be somewhat diagnostic.

So regardless of how good or skilled your doctor is, some uncertainty is inherent in the disease. That makes distinguishing it from other conditions difficult. If any symptoms recur consider seeing a specialist neurologist.

Source: more experience with it than I'd like.