What Causes Purple Rash On Hands?

my friend is male and 67 years old. takes no medication except for daily baby aspirin and occasional Viagra. He has large dark purplish/black "bruising" on the tops of his hands. It is very unsightly and embarrassing to him. I took him to a dermatologist and he was prescribed some meds that were to expensive ($600 plus). I don't remember the name if it. What causes this and is it simply bruising? My father had this as well, but he took blood thinners due to a series of strokes.