Raglet, I am by no means suggesting that you have a certain disorder or disease, BUT I have seen similar stricture of the hand in my mother 10 or so years ago. She was doagnosed at the Mayo as having Shy-Drager a Parkinsons-plus syndrome. It is now called Multiple System Atrophy. She had it for 17 years and ultimately her hands began to atrophy with her fingers curling inward. At that time Mayo was beginning to do clinical trials with a new drug, now known at Botox. They gave her injections into the muscles of her lower arm and hand which allows the muscles to "relax" for a few months at a time. She said, however, that the inections were painful and she ultimately stopped. But that was a long time ago. Perhaps you could ask your physician if they're doing that regularly. I know that aside from Hollywood A-lister getting their faces injected to stop the "worry lines" and "frown line" that it's being used to prevent migraines, stop or reduce excessive sweating and has several benefits.
Botulinium toxin, hey, it's "natural".