Rheumatoid arthritis (RA) is one of the most debilitating types of arthritis. It can cause the joints to swell and eventually become deformed, making it difficult to perform routine tasks.

RA begins in the joints, where two or more bones meet. There are several types of joints. Arthritis occurs mostly in synovial joints, which can move, such as those in the hands, wrists, ankles, knees and feet. For each synovial joint, a space enclosed by the ligaments and adjoining bones forms a cavity called the joint capsule. The outer layer of the capsule is formed by a fibrous membrane. The inside of the capsule is lined with a membrane called the synovium. This membrane secretes synovial fluid, which fills the joint capsule and provides lubrication. The ends of the bones encased in the capsule are cushioned in soft cartilage. The cartilage and synovial fluid permit the bones to move without rubbing against each other.

People with RA experience inflammation in the joint capsules, which affects the movement of the joint and causes pain. RA is an autoimmune condition, which means people with RA have an abnormal immune response. Normally, the immune system protects the body from outside invaders, such as germs. Immune cells (e.g., white blood cells) attack these invaders and flush them out or make them inactive. Part of this process normally produces some inflammation in tissue.

For someone with autoimmune response, the immune system misidentifies regular body tissue as an outside invader. It attacks the tissue and tries to destroy it. In RA, certain types of white blood cells attack parts of the synovium, causing the inflammation that characterizes RA. The process by which this occurs is not well understood. The synovium thickens, which causes the joint to swell. The synovium can form a body called a pannus, which has granular tissue that covers the bone and cartilage. The pannus tissue reacts with enzymes and erodes the bone surface.

RA usually begins in the smaller joints of the fingers or feet. It frequently occurs in the same joints on both sides of the body. It eventually may move to involve more joints, including the wrists, ankles, elbows and knees.

RA is a chronic condition, but attacks may vary. There are periods of severe inflammation called flare-ups, and RA can go into remission for long periods of time. A few people may experience one flare-up followed by remission. However, RA is generally a progressive (worsening) illness. It may start in a few small joints and eventually spread to other joints and tissues, such as cartilage, bones and ligaments. Some RA patients eventually have substantial functional disability that prevents them from working.

RA is a systemic disease, meaning it can involve other body systems. RA can affect the linings of the heart, lungs and blood vessels, and increases the risk of heart disease and heart failure. It can also affect the eyes and the nerves. Inflammation of the blood vessels (vasculitis) can be life-threatening, causing skin ulcerations and infections, bleeding ulcers, hemorrhage and nerve problems.

Rheumatologists classify the status of RA patients based on their ability to function:

• Class I. Completely able to perform usual activities of daily living.
  
  
• Class II. Able to perform usual self-care and work activities, but limited in other activities (i.e., sports or chores).
  
  
• Class III. Able to perform self-care activities but limited in work and other activities.
  
  
• Class IV. Limited in ability to perform usual self-care, work and other activities.

RA can occur at any age and in all races and ethnic groups. It generally begins between the ages of 30 and 50. Although adults are primarily affected, there is also a disease called juvenile rheumatoid arthritis that can affect children.

Women are more commonly affected by RA than men. Of the 1.3 million Americans with RA, at least two-thirds are women, according to the Centers for Disease Control and Prevention (CDC). Women with RA tend to experience remission of symptoms during pregnancy and flare-ups after giving birth or while breastfeeding.

RA is not the same as osteoarthritis (OA), the degenerative form of arthritis most common among elderly people. Although both forms of arthritis cause joint pain, there are several major differences:

• OA involves degeneration of joint cartilage. RA involves inflammation of the membranes lining joints, caused by immune dysfunction.
  

  

• RA usually occurs symmetrically, such as in both hands or both knees. OA may occur on one side (e.g., in one knee).
  
  
• OA affects only the joints. RA can affect other systems in the body, including the lungs, nerves or heart.
  
  
• OA usually affects people over age 50. RA affects people between 20 to 60 years of age.