Scleroderma also affects circulation to the fingers and toes.

I had a patient with this problem, and her hands were turning BLACK and her doctor was discussing amputation after all the drugs tried failed.

She took my advice and did epsom salt soaks for her hands and they started to get better. So I moved her up to oral magnesium (SlowMag), and natural vitamin E to improve her blood flow, and she reversed almost 100%. She had some purple cast now and then, but for the most part her hands were much more normal.
When circulation gets this poor the nerve ending can die off from lack of glucose and oxygen and from the build up of toxins from energy metabolism of the tissues.

So poor circulation from ANY cause is a prime candidate for PN in the hands and feet IMO.