PMDD or Premenstrual dysphoric disorder is a severe case of PMS. While PMS causes a lot of distress. PMDD heightens the symptoms of PMS which in turn affects a person day to day function. The cause for PMDD is unknown however, with hormonal changes in the body compounding the symptoms.
PMDD might worsen symptoms in people who suffer from depression, stress and anxiety.
Sources:
https://www.webmd.com/women/pms/premenstrual-dysphoric-disorder
https://my.clevelandclinic.org/health/articles/9132-premenstrual-dysphoric-disorder-pmdd
https://www.hopkinsmedicine.org/health/conditions-and-diseases/premenstrual-dysphoric-disorder-pmdd