What Causes Itching In Trunk, Arms And Legs Causing Bumps And Sores?

My father 75 is having problems w/ itching mainly trunk but also arms and legs. he has hx of colon ca post colon resection, and single vessel cardiac bypass. recently on prednisone for colitis sx's. no real rash but small bumbs appear after itching, turns into small sore then leaves a scar after healed. also on lasix, K+, lavastatin, metoprolol, lisinopril, thyroid, ASA. Seems to be worse at nite.