Simply put, in bipolar disorder, symptoms of mania or depression are not triggered only by the menstrual cycle, whereas PMDD is triggered entirely by an abnormal brain reaction to the hormone changes across the luteal part of the menstrual cycle.
For those who are unsure if they have PMDD or bipolar disorder then it is important to track your symptoms on a daily basis to see any clear patterns. PMDD will show a very clear ON - OFF pattern around the menstrual cycle. They should also see a skilled Healthcare Professional who can help make a differential diagnosis.
Tracking can help aid an accurate diagnosis. If you feel that bipolar disorder is more fitting to your symptoms but your symptoms ‘flare’ in the luteal phase then you may consider looking into PME - premenstrual exacerbation.