Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. The white discoloration could be a side effect of any previous treatment that you might have been given for your swollen and painful elbow. A lot of sports therapists administer steroid injections into a painful joint or tendon in that region to being down the pain and inflammation. Too superficial injection of steroid can lead to a transient depigmentation. Another possible cause of this white patch could be that it is a vitiligo patch. I suggest you to kindly visit a dermatologist in your region so as to ascertain the exact cause. Hope I have answered your query. Let me know if I can assist you further.