Rheumatoid arthritis: Diagnosis

The American Rheumatism Association criteria for classification of RA are (1987 revision):

Sr. no.	Criteria	Definintion
1.	Morning stiffness	Morning stiffness in and around the joints lasting at least 1 hour before maximal improvement.
2.	Arthritis of three or more joint areas	At least three joint areas simultaneously have soft tissue swelling or fluid (not bony overgrowth alone) observed by a physician. The 14 possible joints are (right or left): PIP, MCP, wrist, elbow, knee, ankle,and MTP joints.
3.	Arthritis of hand joints	At least one joint area swollen as above in wrist, MCP, or PIP joint.
4.	Symmetric arthritis	Simultaneous involvement of the same joint areas (as in 2) on both sides of the body (bilateral involvement of PIP, MCP, or MTP joints is acceptable without absolute symmetry).
5.	Rheumatoid nodules	Subcutaneous nodules, over bony prominences, or extensor surfaces, or in juxta-articular regions, observed by a physician.
6.	Serum rheumatoid factor	Demonstration of abnormal amounts of serum rheumatoid factor by any method that has been positive in less than 5% of normal control subjects.
7.	Radiographic changes	Radiographic changes typical of rheumatoid arthritis on posteroanterior hand and wrist x-rays, which must include erosions or uniequivocal bony decalcification localized to or most marked adjacent to the involved joints (osteoarthritis changes alone do not qualify).

For classification purposes, a patient is said to have rheumatoid arthritis if he or she has satisfied at least four of these seven criteria. Criteria 1 through 4 must be present for at least 6 weeks. Patients with two clinical diagnosis are not excluded. Designation as classic, definite, or probable rheumatoid arthritis is not to be made.

PIP: proximal interphalangeal

MCP: metacarpophalandeal

MTP: metatarsophalangeal

Laboratory abnormalities that may be seen include normocytic, normochromic anemia; thrombocytopenia; leukopenia;elevated erythrocye sedimentation rate (ESR);positive rheumatoid factor (60% to 70% of patients); and positive antinuclear antibodies (ANA) (25% of patients).

Examination of aspirated synovial synovial fluid may reveal turbidity,  leukocytosis, reduced viscosity, and normal or low glucose relative to serum concentrations.

Radiologic findings include soft tissue swelling and osteoporosis near the joint (periarticular osteoporosis). Erosions occurring later in the disease course are usually seen first in the MCP and PIP joints of the hands and metatarsophalangeal (MTP) joints of the feet.