Possible Causes Of Rheumatoid Arthritis - Rheumatoid Arthritis: Arthritis

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Possible causes of rheumatoid arthritis

Scientists don't know what causes rheumatoid arthritis, but they are investigating many hypotheses. The disorder runs in families, is more common among women, and may initially resemble some forms of infectious diseases, such as viral arthritis.

Genetic factors. Rheumatologists have long theorized that some insult (perhaps a microbe or an environmental toxin) triggers rheumatoid arthritis in genetically susceptible people. Now geneticists believe that HLA genes may provide the link. HLA-DR genes — of which several dozen have now been identified — are instrumental in identifying and disposing of foreign antigens. Scientists reported in 1978 that 70% of people with rheumatoid arthritis had molecules of certain DR4 subsets on their lymphocytes, while only 28% of healthy subjects had such molecules. Subsequently, several other genes in the HLA family have been implicated as well.

Infectious agents. Scientists have searched — without success — for evidence that individuals with rheumatoid arthritis might harbor certain bacteria known to cause other types of arthritis, such as Mycoplasma (which causes pneumonia or genital infections) or Chlamydia (one of several sexually transmitted organisms that can cause Reiter's syndrome). A more likely role for bacteria would be through an immune system error: Lymphocytes might produce antibodies against a bacterial product that also react against a connective tissue protein. Other researchers believe that a virus is the most likely culprit.

This form of arthritis attacks multiple joints and is usually symmetrical — it affects joints similarly on both sides of the body, particularly the finger joints, base of the thumbs, wrists, elbows, knees, ankles, or feet. It nearly always involves the wrists and the middle and large knuckles, but seldom the joints nearest the fingertips (see Figure 8). At times, joint pain may be constant, even without movement. Morning stiffness that lasts for an hour or longer is a hallmark of the disease and one of the main ways doctors gauge the severity of inflammation.

The course of rheumatoid arthritis is unpredictable. Early on, the symptoms frequently abate or even disappear, only to flare up weeks or months later. Occasionally complete remission occurs, usually within the first year. But for some people the process is destructive, ending in severe disability within a few years.

Figure 8: Rheumatoid arthritis of the hand An x-ray revealing rheumatoid arthritis of the right hand.

Last updated:	September 05, 2008