Index finger use

I've seen an interview where Keith Richards talked about soaking his hands in very hot water before playing. That's probably great for the joints, but would soften callouses if you kept them in there too long.:hmm

Additionally, I would do a fasting blood test. Ask your doctor to look specifically for high levels of iron (the condition is hemochromatosis). The onset of symptoms are as you describe, in the hands, starting with the tip of the index fingers, and will progress to arthritis. The good news is you can stop this in its tracks, and reverse the symptoms if you start quickly. The therapy is basically that you'll have to give blood several times until your blood iron levels get lower, then give blood on a regular basis (a couple of times a year).