What Is Rheumatoid Arthritis (RA)?

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes the body’s immune system to attack its own tissues, including the delicate tissues that encapsulate most joints.

See Is My Joint Pain Caused by Rheumatoid Arthritis (RA) or Another Autoimmune Disorder?

Rheumatoid arthritis is an autoimmune disease that causes painful swelling, stiffness, and deformities of the joints. Watch: Rheumatoid Arthritis Overview Video

RA can affect almost any joint in the body, but initial symptoms usually affect the wrists, knuckles, balls of the feet, and/or knees. In addition to triggering painful joint swelling and stiffness, rheumatoid arthritis can cause fever and fatigue and potentially lead to long-term joint deformities.

See Hand Rheumatoid Arthritis Signs and Symptoms

Doctors believe early diagnosis and treatment is crucial to limiting potential tissue damage and preserving joint function, but the diagnostic process can be challenging. There is no single lab test that definitively diagnoses RA, and the disease’s onset can vary significantly: one person can develop puffy, stiff wrist and finger joints over many months, while another person develops fatigue, fever, and a severely inflamed knee almost overnight.

See Blood Tests to Help Diagnose Rheumatoid Arthritis (RA)


How Does Rheumatoid Arthritis Progress Over Time?

Regardless of whether symptoms appear gradually over several months or rapidly over weeks, the disease follows the same progression:

  1. The synovial tissue becomes inflamed
    Initially, rheumatoid arthritis is characterized by the inflammation of the synovial tissue. This tissue is found throughout the body, and encapsulates joints and tendons. When synovial tissue is inflamed it can cause pain, stiffness, and swelling in a joint. This condition is called synovitis.
  2. See Conditions Related to Inflammatory Arthritis

  3. Pannus tissue forms
    Inflammation causes the synovial tissue cells to divide and multiply, which causes the synovial tissue to thicken, resulting in more swelling and pain. As cell division continues, cell growth expands into the joint space. This new tissue is called pannus or rheumatoid pannus.
  4. See What Is Pannus?

  5. Cartilage and other joint tissues are damaged
    The pannus cells release enzymes that damage cartilage and underlying bone. Over time, this damage can alter the alignment of the joints, lead to further pain and, in some cases, cause joint deformities.
  6. See What Is Cartilage?

Not all synovial tissue in the body will undergo these changes simultaneously. People with RA typically have certain joints that experience symptoms and other joints that do not.

Who Gets Rheumatoid Arthritis?

Worldwide, experts estimate 0.4 to 1.3% of the population has RA.1,2 In the United States, that means approximately 1.5 million Americans ages 18 and older live with rheumatoid arthritis.3,4

See Lifestyle Factors and Fatigue Associated with Rheumatoid Arthritis (RA)


While the exact cause of rheumatoid arthritis is unknown, researchers believe a combination of genetic, environmental, and hormonal factors are to blame. The condition is two to three times more prevalent in women, and age at the onset of symptoms is generally between 40 and 60 years old.5


  • 1.Silman AJ, Hochberg MC. Epidemiology of the rheumatic diseases. 2nd edition: Oxford University Press; 2001
  • 2.Sacks JJ, Luo YH, Helmick CG. Prevalence of specific types of arthritis and other rheumatic conditions in the ambulatory health care system in the United States, 2001-2005. Arthritis Care Res (Hoboken). 2010;62(4):460-4.
  • 3.Myasoedova E, Crowson CS, Kremers HM, Therneau TM, Gabriel SE. Is the incidence of rheumatoid arthritis rising?: results from Olmsted County, Minnesota, 1955-2007. Arthritis Rheum. 2010;62(6):1576-82. As cited in Arthritis Data and Statistics. Centers for Disease Control and Prevention. Arthritis-Related Statistics. Accessed May 17, 2016.
  • 4.Dugowson CE, Koepsell TD, Voigt LF, Bley L, Nelson JL, Daling JR. Rheumatoid arthritis in women. Incidence rates in group health cooperative, Seattle, Washington, 1987-1989. Arthritis Rheum. 1991;34(12):1502-7.
  • 5.Gabriel SE. The epidemiology of rheumatoid arthritis. Rheum Dis Clin North Am. 2001;27(2):269-81.