There have been quite a few photos of the bruise and the appearance of it seems to be consistent.
The 79-year-old is appearing in public with notable marks and bruises.
www.thedailybeast.com
I've seen a few media reports that the bruising is related to chronic venous insufficiency, but I've seen other reports that contradict this:
>>>Bruising of the hands is not a symptom of chronic venous insufficiency, Dini says. In his letter about Trump, Barbabella attributed this to “minor soft tissue irritation from frequent handshaking and the use of aspirin, which is taken as part of a standard cardiovascular prevention regimen.”<<<
After photographs showed President Donald Trump with swollen ankles and bruised hands, the White House revealed he has chronic venous insufficiency—a blood vessel disease that affects circulation in the legs
www.scientificamerican.com