3. Lupus
Lupus is an autoimmune disease, popularized a few years ago by the hit television show House M. D., that can affect a large number of systems and tissues in your body. Basically, the pathological mechanism behind lupus is an alteration on how your immune system works, causing your immune cells to attack your own tissues. Lupus is difficult to diagnose because symptoms vary widely from case to case, and most of them are very similar to many other conditions.
Perhaps its most characteristic symptom is a butterfly-shaped red rash appearing on the face of the patient, covering the nose and both cheeks. Other symptoms may include fever, joint pain, and swelling, fatigue, chest pain, headaches, and confusion. Just as it happens with arthritis, even if there is no linking mechanism that has been identified by the medical community, it has been observed that people with lupus are more likely to develop fibromyalgia in the future.