How To Treat Hard Callolus Looking Spots On Palm?

I am a 33, 6'5" and 250 lbs. I am also a diabetic, which occurred long after my first onset of symptoms. I have hard, dry dark callolus looking spots that appear on the palm of my hands as well as on the fingers and around the cuticle areas. I have been having them since high school and they normally come and go. No one has been able to give me an exact symptom for what it is. I was once told that it was a vitamin e deficiency and given a topical cream for it. I would like to know how to keep them from coming.