I also have bruising in between my middle knuckles on my left hand. It was only one place 2 days ago and is now spreading. I do not have diabetes or hypertension, but I do have lupus, RA, serjeons, degenerative joint and fibro milage. I have been going to a chiropractor twice a week for cpl weeks now to try to get some relief for extensive pain in neck, left shoulder and left arm. Feels like pinched nerve. But I still can't find an explanation for the sudden bruising knuckles.