Rheumatoid Arthritis Diagnosis
Causes of Rheumatoid Arthritis
The underlying event that promotes RA in a person is unknown. Given the known genetic
factors involved in RA, some researchers have suggested that an outside event occurs that
triggers the disease cycle in a person with a particular genetic makeup.
Many researchers are examining the possibility that exposure to an organism (like a
bacteria or virus) may be the first event in the development of RA. The body's normal
response to such an organism is to produce cells that can attack and kill the organism,
protecting the body from the foreign invader. In an autoimmune disease like RA, this
immune cycle spins out of control. The body produces misdirected immune cells, which
accidentally identify parts of the person's body as foreign. These immune cells then
produce a variety of chemicals that injure and destroy parts of the body.
RA can begin very gradually, or it can strike quickly. The first symptoms are pain,
swelling, and stiffness in the joints. The most commonly involved joints include hands,
feet, wrists, elbows, and ankles, although other joints may also be involved. The joints
are affected in a symmetrical fashion. This means that if the right wrist is involved, the
left wrist is also involved. Patients frequently experience painful joint stiffness when
they first get up in the morning, lasting for perhaps an hour. Over time, the joints
become deformed. The joints may be difficult to straighten, and affected fingers and toes
may be permanently bent (flexed). The hands and feet may curve outward in an abnormal way.
Many patients also notice increased fatigue, loss of appetite, weight loss, and
sometimes fever. Rheumatoid nodules are bumps that appear under the skin around the joints
and on the top of the arms and legs. These nodules can also occur in the tissue covering
the outside of the lungs and lining the chest cavity (pleura), and in the tissue covering
the brain and spinal cord (meninges). Lung involvement may cause shortness of breath and
is seen more in men. Vasculitis (inflammation of the blood vessels) may interfere with
blood circulation. This can result in irritated pits (ulcers) in the skin, tissue death
(gangrene), and interference with nerve functioning that causes numbness and tingling.
Rheumatoid Arthritis Diagnosis - test
- Rheumatoid Factor
This is the most useful diagnostic test because 80% of people with RA
eventually show a high concentration of rheumatoid factor in their
blood. Rheumatoid factor is an antibody produced against immunoglobulin
G. (Antibodies are proteins the body manufactures to fight off foreign
substances). However, since not all people with RA have rheumatoid
factor, and because other diseases can test positive for it, this test
by itself is not conclusive.
- Sed Rate
The sed rate or ESR (erythrocyte sedimentation rate) measures how fast
red blood cells (erythrocytes) fall to the bottom of a glass tube filled
with the patient's blood. The higher the sed rate, the more inflammation
the patient has. Elevated sed rates are usually found with RA, but they
also occur with other conditions.
- Hemocrit
A hemocrit measures of the volume of erythrocytes in the blood. Red
blood cells carry oxygen throughout the body via a pigment called
hemoglobin. A low hemocrit means that a person has too few red cells in
the blood, and therefore too little hemoglobin, resulting in an
insufficient supply of oxygen to the cells. This is called anemia.
Anemia is common with RA. Many other conditions, however, can also cause
anemia.
- Synovial fluid analysis
Synovial fluid is obtained through arthrocentesis. In this procedure
fluid is withdrawn from a joint and analyzed. Active inflammation makes
synovial fluid cloudy and abnormally thin, with higher than normal
protein and white blood cells. Conditions other than RA can produce
these abnormalities.
- Radiology
X-rays can reveal cartilage damage that causes joint space narrowing.
They can also show bone erosion and localized osteoporosis. In the early
stages of RA, x-rays are not very useful since joint damage is usually
not present. When several joints are involved, however, a physician may
elect to x-ray one joint (usually hands) as a baseline for comparison
over time.
More detailed information about Rheumatoid Arthritis Diagnosis
There are no tests available that can absolutely diagnose RA. Instead, a number of
tests exist that can suggest the diagnosis of RA. Blood tests include a special test of
red blood cells (called erythrocyte sedimentation rate), which is positive in nearly 100%
of patients with RA. However, this test is also positive in a variety of other diseases.
Tests for anemia are usually positive in patients with RA, but can also be positive in
many other unrelated diseases. Rheumatoid factor is an autoantibody found in about 66% of
patients with RA. However, it is also found in about 5% of all healthy people and in
10-20% of healthy people over the age of 65. Rheumatoid factor is also positive in a large
number of other autoimmune diseases and other infectious diseases.
A long, thin needle can be inserted into a synovial joint to withdraw a sample of the
synovial fluid for examination. In RA, this fluid has certain characteristics that
indicate active inflammation. The fluid will be cloudy, relatively thinner than usual,
with increased protein and decreased or normal glucose. It will also contain a higher than
normal number of white blood cells. While these findings suggest inflammatory arthritis,
they are not specific to RA. |
