Premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD) both share the same set of physical and emotional symptoms, which occur prior to the start of the menstrual cycle. Where they differ, however, is in the severity of their emotional symptoms and the fact that they may interfere with daily functioning. For example, a woman with PMS might feel mild depression prior to her period, where a woman with PMDD might experience severe, debilitating depression.
PMDD is also less common than PMS. While about 20% to 50% of women will experience PMS symptoms, only about 3% to 5% of them will experience symptoms severe enough to meet the DSM-IV diagnostic criteria for PMDD.
Source:
Jacobson, James L. and Alan M. Jacobson. Psychiatric Secrets. 2nd ed. Philadelphia: Hanley & Belfus, 2001.
