Endometriosis, a disease in which tissue of the uterus is on the outside of the uterus and in other parts of the body, can be a source of severe pain and infertility. Endometriosis is caused by a hormonal immune system that may also contribute to many other conditions including irritable bowel syndrome (IBS), migraine headaches, allergies, hypothyroidism, autoimmune disorders and heart disease. Gynecologist Karen Wang, M.D., discusses the complexity of diagnosis and treatment of the condition.