Ego-syntonic means that the behavior is in "sync" with one’s self image/beliefs (ego). They don't realize that their actions are wrong, which causes no mental conflict/guilt as a result of his actions and is therefore difficult to treat.
Ego-dystonic means that the behavior is out of "sync" with one’s self image/beliefs (ego). They realize that their actions are wrong, which causes mental conflict and therefore they are easier to treat with CBT etc.