How is rheumatoid arthritis diagnosed?
Rheumatoid arthritis diagnosis can be difficult; specially if it’s early in the course of the disease. There is no one test that will definitively diagnose rheumatoid arthritis (RA). For example, the blood tests may be negative in someone who has rheumatoid arthritis and positive in someone else who doesn’t. In early rheumatoid arthritis, the xrays may be completely normal. A skilled rheumatologist is able to carefully investigate all the available data and determine if someone has rheumatoid arthritis.
Besides a careful history and physical exam, several clues can help in the rheumatoid arthritis diagnosis process:
When rheumatoid arthritis is suspected clinically, certain laboratory tests can help confirm the diagnosis.
Rheumatoid factor (RF)– rheumatoid factor is present in about 80% of people with rheumatoid arthritis. In about 20% of people, the diagnosis established in the absence of this antibody. False positive rheumatoid factor can be seen in a minority of healthy people and can be associated with bacterial endocarditis, hepatitis C, chronic liver disease, sarcoidosis, or aging.
Anti-citrullinated peptite antibody (ACPA or anti-CCP)– these antibodies can also be seen in about 70% of people with rheumatoid arthritis. CCP is more specific than rheumatoid arthritis for diagnosis of RA.
It is possible to have rheumatoid arthritis with a negative RF and CCP. These cases are called “seronegative” RA. Presence of RF and/or CCP antibodies are associated with a more aggressive disease.
Other laboratory abnormalities
People with rheumatoid arthritis commonly have elevated inflammatory markers erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Anemia of chronic disease is not uncommon. They may also have a low positive anti-nuclear antibody (ANA).
Xrays are commonly obtained at the time of rheumatoid arthritis diagnosis. Xrays of the hands and feet are most commonly taken, since these are the areas most affected by RA. In early RA, xrays may be normal. As the disease progresses RA-specific findings may become apparent on the xrays including thinning of the bone around a joint, narrowing of the joint, subluxation and deformity of a joint, and erosions around the joint. Xrays are also used during the treatment of rheumatoid arthritis to assess response to treatment and ensure the disease is not progressing.
MRI is sometimes used in the diagnosis of rheumatoid arthritis when it is highly suspected but the antibodies are negative and xrays are normal. Presence of synovitis- inflammation of the joint- or bony erosions typical of RA help confirm the diagnosis.
The use of ultrasound is becoming increasingly popular both in the diagnosis and followup of RA, since it is a relatively inexpensive and noninvasive procedure that can be easily performed in the office. Studies have shown that ultrasound can be as sensitive as MRI in picking up joint inflammation and erosion. The accuracy of the ultrasound findings depends on the expertise of the person performing the ultrasound.
Examination of fluid from a swollen joint can be helpful to distinguish rheumatoid arthritis from osteoarthritis, gout, or infection. Unlike the fluid from an osteoarthritic joint, the RA joint fluid will show abundant inflammation. Presence of uric acid crystals in the joint fluid may indicate that gout is the correct diagnosis.
Classification criteria for RA were originally designed to for research purposes, but have been used by many physicians as a means to confirm the diagnosis of rheumatoid arthritis.
The initial criteria were first established in 1987 jointly by the American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR). It required presence of symptoms for at least 3 months, and at least 4 out of 7 criteria to classify as RA.
The 1987 ACR/EULAR classification criteria for rheumatoid arthritis
|1. Morning stiffness
|Morning stiffness in and around the joints, lasting at least 1 hour
|2. Arthritis of ≥3 joints
|The qualified areas are PIP, MCP, wrist, elbow, knee, ankle, and MTP joints
|3. Arthritis of hand joints
|At least 1 area swollen in a wrist, MCP, or PIP joint
|4. Symmetric arthritis
|Simultaneous involvement of the same joint areas on both sides of the body
|5. Rheumatoid nodules
|Subcutaneous nodules over bony prominences, extensor surfaces, or around joints
|6. Rheumatoid factor
|Positive rheumatoid factor
|7. Radiographic changes
|Including erosions or periarticular demineralization
As advances in diagnostic abilities allowed for earlier diagnosis of rheumatoid arthritis, the 1987 criteria was criticized for not allowing for early diagnosis of RA. For example, people with early rheumatoid arthritis may not have rheumatoid nodules or any radiographic changes.
The most recent ACR/EULAR rheumatoid arthritis classification criteria, introduced in 2010, has been useful to diagnose RA earlier than the previous criteria. A total of 6 points is required to meet the criteria.
This criteria is used most often to establish early diagnosis of RA. It is recognized that some people with longstanding RA may qualify the 1987 criteria but not the ones from 2010. Large joints refers to shoulders, elbows, hips, knees, and ankles. Small joints refers to metacarpophalangeal (MCP) joints, proximal interphalangeal (PIP) joints, 2nd-5th metatarsophalangeal joints, thumb interphalangeal joints, and wrists.
Why is it important to diagnose rheumatoid arthritis early?
The goal in management of rheuamtoid arthritis is to control the symptoms and prevent joint damage. In the past several years, studies have shown that the earlier the rheumatoid arthritis diagnosis is established, and the earlier treatment is initiated, the better the outcome of the disease. For this reason, it is important to diagnose rheumatoid arthritis as early as possible.