Oops looks like we missed this one..

I don't have an answer for your question though-
I have more loss of fine finger coordination and sometimes aches or pains in the back of hands or the wrist joint gets sore - but nothing that you can see like you describe.

just totally guessing here -- it could be due to maybe the angles or positions your arm is in- causing a little compression on the nerve or a vein, does it fade away after you stop writing?