I once found temporary relief in doing the "Bridge Pose". I actually got back the strength in my hand and I could write like I always was able. But the response only stayed for a couple of days and then the hands went back to losing muscle tension even when I did the Bridge Pose again.
I can actually write better when I'm standing and writing against a wall, with my arm fully extended and my wrist bent. That sounds like a problem in the elbow or shoulder, doesn't it?