There are about 125 arthritic diseases that affect up to 50 million Americans. They have different causes, treatments and outcomes, but they have in common the potential destruction of joints and pain. Most forms can be controlled with lifestyle changes, drugs or surgery.

Osteoarthritis. The most common form, associated with "wear and tear," or aging. Responds to exercises and physical therapy. Most serious cases benefit from surgical joint replacement. Strikes about 15 million people.

Rheumatoid arthritis. A systemic inflammatory disease involving the destruction of collagen, the connective tissue that is an integral part of cartilage, the elastic tissue that keeps joints moving. Disabling, painful and depressing. Sometimes responds to powerful drugs; helped by aspirin and other anti-inflammatory painkillers. Surgery beneficial in some cases. Exercise, particularly swimming and walking, support groups and relaxation techniques are recommended to help manage symptoms and control pain. Affects about 2.5 million.

Fibromyalgia; other soft-tissue rheumatisms. A group of diseases characterized by muscle and joint pain, fatigue, stiffness, general aching with tender spots. Low to moderate aerobic exercise and relaxation techniques recommended. An estimated 6 million are affected.

Lupus (systemic lupus erythematosus). A systemic disease in which the immune system mistakenly attacks the body's own tissues and leads to inflammatory arthritic symptoms. Also affects skin, kidneys, muscle tissue and the brain. Strikes one in 700 white women and one in 250 black women.

Spondyloarthropathies. A group of diseases that involve the stiffening of the spine. Also can affect eyes, genito-urinary tract. Sometimes linked to venereal diseases such as chlamydia and gonorrhea. Affects an estimated 100,000. More common in young men, rare in women.

Juvenile arthritis. A group of inflammatory arthritic diseases that affects about 200,000 children and adolescents. Symptoms sometimes reduced in adulthood. May involve high, spiking fevers and rashes.

Gout. Disorder caused by collection of uric acid crystals in a joint, often a toe. Affects men at or after middle age, linked to overweight and sedentary lifestyle. Successfully treated with drug therapy. Strikes 5 percent of white men over age 65.