In case anyone cares, the Scientific American article actually has a typo:
(emphasis added)
The sentence should read, “The other classic syndrome is called progressive bulbar palsy—or progressive supranuclear palsy”. (with ‘bulbar’ referring to the brain stem)
Well, OUR medical knowledge of his case here on the straightdope is pretty darned limited. Particular in comparison to the knowledge possessed by his doctors, ie, all of it. I’m fine siding with the best doctors in the world here.
I’ve always heard that ALS is traditionally diagnosed via “exhaustion”, in that they basically have to rule a bunch of stuff out that can be diagnosed more directly and presents with similar symptoms before settling on ALS.
(I only know anything about ALS because of involvement with ALS charities, not through any expert level knowledge.)
The “About” page on the ALS Association website seems to suggest this is still how it is done:
I can confirm this from more direct experience (stepfather, alas). And so it stands to reason that a disease which is diagnosed by process of elimination is more likely than most to actually be an umbrella term for what are really, in some sense, different diseases.