Dean was an internal medicine specialist. I say "was" because he hasn't practiced in more than a decade. Details of Dean's medical career have always been sketchy; I've heard rumors that he might have lost a couple of high-dollar malpractice suits, and that helped convince him to give up medicine.
By comparison, Bill Frist was one of the nation's preeminent heart surgeons before entering politics; and he graduated at the top of his class from Harvard Medical School.