This could be carpal tunnel syndrome which causes clamping up of fingers etc. The cure is to cut a tendon on the wrist, a simple procedure that the doctor can do.
Can be caused be too much pressure on the hands, e.g cycling hands on handlebars, or using a keyboard, or not using your hands and fingers enough. I have this and when it happens I pull the hand and fingers back out of it its painful I know, its like cramp where you just yank your leg straight to pull the muscle out.