Arthritis is a general term for approximately 100 diseases that produce either INFLAMMATION of connective tissues, particularly in joints, or noninflammatory degeneration of these tissues. The word means "joint inflammation," but because other structures are also affected, the diseases are often called connective tissue diseases. The terms rheumatism and rheumatic diseases are also used. Besides conditions so named, the diseases include gout, lupus erythematosus, ankylosing spondylitis, degenerative joint disease, and many others, among them the more recently identified LYME DISEASE. Causes of these disorders include immune-system reactions and the wear and tear of aging, while research indicates that the nervous system may often be equally involved. About one out of seven Americans exhibit some form of arthritis. INFLAMMATORY CONNECTIVE TISSUE DISEASES This varied group of diseases produces inflammation in the connective tissues, particularly in the joints. The signs of inflammation--warmth, redness, swelling, and pain--may be apparent. Microscopic examination of the lesions reveals prominent blood vessels, abnormal accumulations of white blood cells, and varying degrees of wound healing with scarring. In some diseases, the inflammation is clearly an immune reaction, the body\'s defense against invading microorganisms. In others, the cause is different or unknown. Infectious Arthritis This disease is most common in young adults. Infection in a joint is usually caused by bacteria or other microorganisms that invade the joint from its blood vessels. Within hours or a few days the joint, usually the knee or elbow, becomes inflamed. There is an abnormal accumulation of synovial, or joint, fluid, which may be cloudy and contain large numbers of white blood cells. Gonococcal arthritis, a complication of gonorrhea, is the most common form of infectious arthritis. Treatment with antibiotics and aspiration of synovial fluid is usually promptly effective, and only minor residual damage is done to the joint. Occasionally the infection is prolonged and produces joint destruction and requires surgery. Rheumatic Fever This is a form of infectious arthritis caused by hemolytic streptococcus, a bacterium. Unlike typical infectious arthritis, however, the disease is most common in children aged 5 to 15 years, begins weeks after the onset of the streptococcal infection, and streptococci cannot be isolated from the joint fluid. The inflammatory process may involve the heart and produce rheumatic heart disease. The symptoms of RHEUMATIC FEVER usually occur 2 to 3 weeks after the onset of a severe streptococcal sore throat. Acute pain and swelling "migrate" from joint to joint over a period of several days. The inflammation, which persists for less than three months, can usually be controlled by aspirin and rest, and it produces no residual deformity. Less than 1 percent of children with streptococcal sore throats develop rheumatic fever, and a small number of these will develop rheumatic heart disease. Rheumatic fever only rarely occurs if the streptococcal sore throat is treated early with an antibiotic such as penicillin. The inflammation of the joints and the heart in rheumatic fever apparently occurs because the body\'s immune response to the streptococcus damages tissues. For this reason, rheumatic fever has been termed an autoimmune disease. Gout and Pseudogout The inflammatory process in these diseases is unrelated to infection. Rather, inflammation is incited by the deposition in the joint of uric acid present in the bloodstream. An attack of acute gouty arthritis is caused by the formation of needlelike crystals of the deposited uric acid. When these crystals are ingested by white blood cells, the cells release enzymes that evoke inflammations. Uric acid is a normal breakdown product of urine metabolism. Abnormally elevated blood levels of uric acid, which are associated with gouty arthritis, arise through either excessive production of uric acid or decreased excretion of uric acid by the kidneys. Some cases of hyperuricemia and gout are caused by known specific enzymatic defects. Many are associated with metabolic alterations that occur in obesity. When extreme, the gouty process results in large deposits of uric acid, or tophi, around joints. Acute attacks subside when the patient receives anti-inflammatory drugs. Further attacks may be prevented by colchicine, a drug that inhibits the ingestion of crystals by white blood cells. Serum uric acid levels decline and tophi resolve when the excess uric acid production is controlled by weight reduction and by drugs such as allopurinol, a purine analog that inhibits both formation of purines and