Medical School (Psychiatrist) is an extremely harsh environment
Everyone who has gone through Internship comes out... changed
It is hard to explain, but the closest similar process is active combat
Most physicians are examples of PTSD to some degree
PhD Psychologist is a very different trading path
A psychopaths is not affected by stress in the same way psychotypical people are, so it would stand to reason he would be able to handle the pressure of medical school quite easily. At the same time, he would probably adopt a facade of PTSD as a socially acceptable mask.