Hi and welcome to Healthcare magic.Thank you for the query.
It can be damage of nerves in shoulder are or compression of nerves in neck area which is called thoracic outlet snydrome.YOu should do x ray
check to find is there any particular cause. Secondly it can be any kind of neuropathia and if nothing is found on tests, then nerve biopsy
may be necessary
Wish you good health. Regards