What is the difference between a major depressive disorder and a dysthymic disorder?

Intensity. Dysthymic patients are sad, unhappy & have no joy in life to a good instance but not as severe as majot depression hen pts will be totally wihdrawn, no social interactions or motivation to the point of being affecting their daily life.
Intensity & duration. Dysthymia, aka neurotic depression, is a mood disorder consisting of chronic depression, w/ less severe but longer lasting symptoms than mdd. According to the dsm's definition of dysthymia, it is a serious state of chronic depression, which persists for at least 2 years; it is less acute and severe than mdd (which though more severe, can be as brief as 2 weeks).