American physician here. I don't speak French but it does not sound like one needs to for this.
You are right to be irritated, "brain trouble" is extremely non-specific. Anything in the entire textbook of neurology could fit.
You mention multiple sclerosis, alcoholism, intoxication of any kind, but equally a hundred other things.
The term may have had some specific cultural meaning "between the lines" in that time and place, but if so I do not know it. Sorry.

Robert Roth MD
Kingston NY USA