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Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic, inflammatory autoimmune disorder that causes the immune system to attack the joints. It is a disabling and painful inflammatory condition, which can lead to substantial loss of mobility due to pain and joint destruction. The disease is also systemic in that it often also affects many extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and muscles.

Derived from the Greek rheumatos= flowing, -oid= in the shape of, arthr= joint, itis= condition involving inflammation

Symptoms of Rheumatoid Arthritis

The American College of Rheumatology has defined (1987) the following criteria for Rheumatoid Arthritis:

  • Morning stiffness of >1 hour.
  • Arthritis and soft-tissue swelling of >3 of 14 joints/joint groups
  • Arthritis of hand joints
  • Symmetric arthritis
  • Subcutaneous nodules in specific places
  • Rheumatoid factor at a level above the 95th percentile
  • Radiological changes suggestive of joint erosion

Four criteria have to be met, although many patients are treated despite not meeting the criteria.

The symptoms that distinguish rheumatoid arthritis are inflammation and soft-tissue swelling of many joints at the same time (polyarthritis). The hands are generally affected in a symmetric fashion. The pain generally improves with use of the affected joints, and there is usually stiffness of all joints in the morning that lasts over 1 hour.

If the arthritis has been longstanding, the inflammatory activity has led to erosion and destruction of the joint surface, which impairs their range of movement and leads to deformity. The fingers are typically deviated towards the little finger (ulnar deviation) and can assume unnatural shapes.

Subcutaneous nodules on extensor surfaces, e.g. the elbows, are often present.

Diagnosis of Rheumatoid Arthritis

When RA is being clinically suspected, immunological studies are required, such as rheumatoid factor (RF, a specific antibody). A negative RF does not rule out RA; rather, the arthritis is called seronegative. During the first year of illness, rheumatoid factor is frequently negative. 80% patients eventually convert to seropositive status. RF is also seen in other illnesses, like Sjogren's syndrome, therefore the test is not very specific. Because of this low specificity, a new serological test has been developed in recent years, which tests for the presence of so called anti-citrullinated protein (ACP) antibodies.

Like RF, this test can detect approximately 80% of all RA patients, but is rarely positive in non-RA patients, giving it a specificity of around 98%. In addition, ACP antibodies can be often detected in early stages of the disease, or even before disease onset. Currently, most common test for ACP antibodies is the anti-CCP (cyclic citrulinated peptide) test. Also, several other blood tests are usually done to allow for other causes of arthritis, such as lupus erythematosus. The erythrocyte sedimentation rate (ESR), C-reactive protein, full blood count, renal function, liver enzymes and immunological tests (e.g. antinuclear antibody/ANA) are all performed at this stage. Ferritin can reveal hemochromatosis, which can mimic RA.

Pathophysiology

The cause of Rheumatoid Arthritis is unknown, but long suspected to be infectious. Mycoplasma, Erysipelothrix, Epstein-Barr virus, parvovirus and rubella have been suspected but never supported in epidemiological studies. As in other autoimmune diseases, the "mistaken identity" theory suggests that an offending organism causes an immune response that leaves behind antibodies that are specific to that organism. The antibodies are not specific enough, though. They begin an immune attack against, in this case, the synovium, because some molecule in the synovium "looks like" a molecule on the offending organism that created the initial immune reaction.

Autoimmune diseases require that the affected individual have a defect in the ability to distinguish self from foreign molecules. This ability is acquired in the first year of life. There are markers on many cells that confer this self-identifying feature. However, some classes of markers allow for RA to happen. 90% of patients with RA have the cluster of markers known as the HLA-DR4/DR1 cluster, whereas only 40% of controls do. Thus, in theory, RA requires susceptibility to the disease through genetic endowment with specific markers and an infectious event that triggers an autoimmune response.