Arthritis Diagnosis 

Imaging 

X-rays of the hands and feet are generally performed in  people with a polyarthritis. In rheumatoid arthritis, there may be no changes in the early stages of the disease,  or the x-ray may demonstrate juxta-articular osteopenia, soft tissue swelling and loss of joint space. As the disease advances, there may be bony erosions and sublaxation. X-rays of other joints may be taken if symptoms of pain or swelling occur in those joints. 

Other medical imaging techniques such as magnetic resonance imaging and ultrasound are also used in rheumatoid arthritis. 

Blood tests 

When RA is clinically suspected, immunological studies are required, such as testing for the presence of rheumatoid factor (RF,  a specific antibody).[7] A negative RF does not rule out RA; rather, the arthritis is called seronegative. This is the case in about 15% of patients.[8] During the first year of illness, rheumatoid factor is more likely to be negative with some individuals converting to seropositive status over time. RF is also seen in other illnesses,  for example Sjögren's syndrome, and in approximately 10% of the healthy population, therefore the test is not very specific. 

Because of this low specificity, new serological test have been developed, which tests for the presence of so called anti-citrullinated protein antibodies (ACPAs). Like RF, these tests are positive in only  a proportion (67%) of all RA cases, but are rarely positive  if RA is not present, giving it a specificity of around 95%.[8] As with RF, there is evidence for ACPAs being present in many cases even before onset of clinical disease. 

The most common tests for ACPAs are the anti-CCP (cyclic citrullinated peptide) test and the Anti-MCV assay (antibodies against mutated citrullinated Vimentin). Recently a serological point-of-care test (POCT) for the early detection of RA has been developed. This assay combines the detection of rheumatoid factor and anti-MCV for diagnosis of rheumatoid  arthritis and shows  a sensitivity of 72%  and specificity of 99.7%. 

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 other immunological tests (e.g. antinuclear antibody/ANA) are all performed at this stage. Elevated ferritin levels can reveal hemochromatosis, a mimic RA, or be a sign of Still's disease, a seronegative, usually juvenile, variant of rheumatoid 

Diagnostic criteria 

The American College of Rheumatology has defined (1987) the following criteria for the classification of rheumatoid arthritis: 

• Morning stiffness of >1 hour most mornings for at least 6 weeks. 
• Arthritis  and soft-tissue swelling of >3 of 14 joints/joint groups, present for at least 6 weeks 
• Arthritis of hand joints, present for at least 6 weeks 
• Symmetric arthritis, present for at least 6 weeks 
• Subcutaneous nodules in specific places 
• Rheumatoid factor at a level above the 95th percentile 
• Radiological changes suggestive of joint erosion 

At least four criteria  have to be met  for classification as RA. These criteria are not intended for  the diagnosis for routine clinical care; they were primarily intended to categorize research. For example: one  of the criteria is the presence of bone erosion on X-Ray. Prevention of bone erosion is one of the main aims of treatment because it is generally irreversible. To wait until all of the ACR criteria for rheumatoid  arthritis are met  may sometimes result in a worse outcome. Most sufferers and rheumatologists would agree that it would be better to treat the condition as early as possible and prevent bone erosion from occurring, even if this means treating people who don't fulfill the ACR criteria. The ACR criteria are, however, very useful for categorising established rheumatoid arthritis, for example for epidemiological purposes. 

Differential diagnosis 

Several other medical conditions can resemble RA, and usually need to be distinguished from it at  the time  of diagnosis: 

• Crystal induced  arthritis (gout, and pseudogout) - usually involves particular joints and can be distinguished  with aspiration of joint fluid if in doubt 
• Osteoarthritis - distinguished with X-rays of  the affected joints and blood tests 
• Systemic lupus erythematosus (SLE) - distinguished by specific clinical symptoms and blood tests (antibodies against double-stranded DNA) 
• One of the several types of psoriatic arthritis resembles RA - nail changes and skin symptoms distinguish between them 
• Lyme disease causes erosive arthritis and  may closely resemble RA - it may be distinguished by blood test in endemic areas 
• Reactive arthritis (previously Reiter's disease) - asymmetrically involves heel, sacroiliac joints, and large joints of the leg. It is usually associated  with urethritis, conjunctivitis, iritis, painless buccal ulcers, and keratoderma blennorrhagica. 
• Ankylosing spondylitis - this involves  the spine  and is usually diagnosed in males, although a RA-like symmetrical small-joint polyarthritis  may occur in  the context of this condition. 

Rarer causes that usually behave differently but may cause joint pains: 

• Sarcoidosis, amyloidosis,  and Whipple's disease can also resemble RA. 
• Hemochromatosis may cause hand joint arthritis. 
• Acute rheumatic fever can be differentiated from RA by a migratory pattern of joint involvement and evidence of antecedent streptococcal infection. Bacterial arthritis (such as streptococcus) is usually asymmetric, while RA usually involves both sides of the body symmetrically. 
• Gonococcal arthritis (another bacterial arthritis) is also initially migratory and can involve tendons around the wrists and ankles.