Arthritis

I

Introduction

Arthritis, any of more than 100 different diseases causing pain, stiffness, and in most cases, swelling in the joints. According to the National Arthritis Foundation, arthritis is the number-one cause of physical disability, affecting more than 20 percent of all Americans and about 50 percent of those over 65. Arthritis affects people of both sexes and of all races, socioeconomic levels, and geographic areas. Although most forms of arthritis are more common in adults, about 300,000 children in the United States suffer from some type of arthritis-related disease.

Arthritis affects movable joints, that is, those joints where bones meet and move relative to one another. Movable joints cushion the bones and prevent them from rubbing against each other during movement. These joints are composed of cartilage—smooth, elastic tissue—surrounded by a casing called the joint capsule. The joint capsule is lined with a synovial membrane that secretes synovial fluid, a liquid that fills the joint cavity and further reduces friction between the bones. Although all arthritic conditions involve joint pain, the severity, duration, and effects of this pain vary considerably from one condition to another.

II

Kinds of Arthritis

A

Osteoarthritis

The most common form of arthritis is osteoarthritis (OA), also known as degenerative joint disease. The disease is most prevalent in people aged 55 and older, and it affects more women than men. In OA, the cartilage cushion in the joints breaks down, causing the bones to rub together. Pain, stiffness, and sometimes the formation of bone growths, called spurs, result. OA can affect any joint, but it is most common in the hands, feet, spine, and large, weight-bearing joints such as the hips and knees.

Although OA is often attributed to general wear and tear associated with aging, it can also be caused or exacerbated by a number of other problems, including obesity, injury, or repeated joint stress. Many researchers believe that OA is in part hereditary, and may be due to genetic abnormalities in the cells that produce cartilage.

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B

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is often regarded as the most serious, painful, and disabling of all forms of arthritis. RA usually begins between the ages of 20 and 40 and is three times more likely to affect women than men. RA occurs most often in the same joints on both sides of the body, such as the hands, wrists, elbows, shoulders, knees, ankles, and feet.

RA is a type of inflammatory arthritis. As the name implies, inflammatory types of arthritis are characterized by inflammation in joints and tendons. In inflammatory arthritis, the synovial membrane becomes swollen and inflamed, causing pain and stiffness. Chemicals released in the inflamed tissue increase blood flow to the joint, causing it to look red and feel warm to the touch. To reduce pain, patients with arthritis may favor affected joints, holding them in a fixed position. This causes the muscles surrounding the joints to stiffen and weaken and the tendons, which attach muscles to bone or to other muscles, to tighten. As a result, joints may contract or change shape and patients may eventually lose mobility.

Rheumatoid arthritis is an autoimmune disease—that is, a disease in which the body’s disease-fighting immune system attacks its own healthy tissues. In RA, the immune system attacks the synovium. The resulting inflammation can lead to widespread and severe joint damage, which may eventually restrict a patient’s mobility. In severe cases, the bone itself erodes and joints may dislocate, causing the joint to freeze in one position.

The causes of arthritis-related autoimmune responses are not well understood, but scientists believe genetics may play a role. Although some genes have been identified that predispose people to RA, these genes are not the only factor. Researchers continue to search for other genes involved, and for external triggers, such as viruses, bacteria, or other environmental agents, that may set off the disease in genetically predisposed people.

C

Juvenile Rheumatoid Arthritis

Juvenile rheumatoid arthritis (JRA) is the most common form of arthritis in children. JRA causes pain, swelling, and stiffness. It can be mild and disappear after several years, or in severe cases, JRA can last a lifetime. There are three forms of JRA: systemic JRA, polyarticular JRA, and pauciarticular JRA.

Systemic JRA, commonly known as Still’s disease, accounts for 10 to 20 percent of all JRA cases. It first appears as a high fever and characteristic rash, followed sometimes months later by joint pain and swelling. Still’s disease may also affect children’s internal organs, causing, for instance, swelling of the outer lining of the heart, the heart itself, or the lungs. Although most of the problems associated with Still’s disease usually subside within a few months, the arthritis may persist into adulthood.

Polyarticular JRA starts with pain, stiffness, and swelling in five or more joints, usually the small joints of the fingers and hands, accompanied by a low fever. Polyarticular JRA often affects the same joints on both sides of the body. The third type of JRA, pauciarticular JRA, affects four or fewer joints—usually the large joints on only one side of the body. In most children, arthritis disappears after several years, but joint stiffness and damage can persist into adulthood.