Let’s say that Lou Kowalski, dockworker, started having the same muscle coordination problems that Lou Gehrig had. He goes to the doctor, doc acknowledges he has some problems, and diagnoses. . . what?
Gehrig was diagnosed with ALS at the Mayo Clinic, so I understand, which was not a likely destination for most people. So what might the “average” doctor/neurologist in the “average” city have likely diagnosed. ALS had been documented by that time, but was it something that might have been considered?
Keep in mind that diagnostic medicine in 1939 was nothing near what it was today. A lot of doctors would have guessed polio (indeed, up into the 50’s and 60’s there was a common perception that Gehrig had died from a form of polio called ALS), some might have guessed muscular dystrophy (if you think about it, MD isn’t a name as much as a description), some might have guessed Parkinson’s disease or any other neuromuscular disease.
Most likely, your average doctor who hadn’t had experience with ALS would have fallen back on some catchall term like “wasting syndrome,” ataxia or chorea.