Kidney disorders, Liver disease, blood disease, hormone imbalance, growths pressing on nerves,
vitamin E, b1,
b6, b12 and niacin deficiencies, alcoholism,
carpal tunnel, ulnar/peroneal/radial nerve palsy, arm position putting pressure on nerves in neck/spine.
If it is in the neck, great, but I think it's best to check for other more serious issues first because the sooner they are addressed the better.