Are lupus and fibromyalgia related? How are they diagnosed?

Fibromyalgia typically presents with generalized muscle pain and fatigue, symptoms that are common in SLE. however, SLE causes multiple symptoms and signs, including skin rash, joint swelling and often lung, heart and kidney abnormalities, none of which are present in fibromyalgia. SLE is also characterized by immune related laboratory findings.
However, 20-40% of patients with lupus also have concurrent fibromyalgia.
Rheumatologists generally can differentiate SLE from fibromyalgia by a careful history and physical examination.