Timeframe & technology: similar to 1920s/1930s
Basically -- Character A, a man in his 40s and in generally good health otherwise -- barring smoking -- needs to fall very, very sick, very slowly. For story reasons, it can't be the obvious culprit of tuberculosis. I'm seeking a disease that was hard to treat prior to antibiotics, produces nonspecific symptoms at the start, progresses over the course of a year or so (not too fussy about the specific length here, but it has to be at least several months) and eventually renders him bedridden (and possibly kills him), but without affecting his mental abilities very much.
The illness can be infectious or genetic.
I would also like to know what sort of treatment would have been available for said disease in that timeframe.
Research done: to be honest, not very much. I'm not entirely sure where to start looking with this. A lot of long-term, inherited fatal illnesses I can think of tend to affect cognition, but I need him to be in relatively sound mind up 'til the end.
Thanks in advance!