It is a syndrome in the sense that it can appear by itself and accompany other conditions such as infections, trauma both emotional or physical, inflammatory rheumatic conditions or by itself. It is not an auto-immune disorder. It is more of a sign and symptom complex of increased perception of pain. It can cause joint pain, and patients may confuse it with arthritis, but arthritis requires joint swelling. In Fibromyalgia, there is no joint swelling.
Diagnosis is made by a symptom complex.
In Fibromyalgia, there is muscle pain. That's what's characteristic of the condition. In addition to the muscle, the pain is above and below the waist and the patients have an exam to assess these areas of extreme tenderness, so called trigger points. These trigger points are distributed anatomically in a way in which you can examine exactly where those tender spots are. The diagnosis is a diagnosis of exclusion.