The Arthritis Foundation says:
Fibromyalgia is a syndrome characterized by long-lasting widespread pain and tenderness at specific points on the body. The term “fibromyalgia” means pain in the muscles, ligaments and tendons. Although not defining characteristics, sleep disturbances and fatigue are also integral symptoms of fibromyalgia.
This condition is referred to as a syndrome because it’s a set of signs and symptoms that occur together with no known cause or identifiable reason. Although considered an arthritis-related condition, fibromyalgia is not truly a form of arthritis because it does not cause inflammation or damage to the joints, muscles or other tissues. It is, however, considered a rheumatic condition because it impairs the joints and/or soft tissues and causes chronic pain.
Fibromyalgia is an especially confusing and often misunderstood condition. Because its symptoms are quite common and laboratory tests results generally are normal, people with fibromyalgia were once told that their condition was “all in their head.” However, medical studies have proven that fibromyalgia does indeed exist, and it is estimated to affect about two percent of the U.S. population today.
More information is available here.
Psoriatic arthritis is an inflammatory joint disease associated with psoriasis, a chronic skin disease. It is estimated that between five and 23 percent of people with psoriasis will develop psoriatic arthritis. The joint disease can present itself in a variety of ways and its symptoms can be similar to those of various other forms of arthritis. On average, joint disease appears about 10 years after the first signs of psoriasis.
Psoriasis is an inflammatory skin disease … The fingernails and toenails also are commonly affected by psoriasis, with pitting, separation of the nail from the underlying nail bed, and transverse ridging and cracking. Nail involvement is the only clinical feature that identifies patients with psoriasis who are likely to develop arthritis.
