Classification of inflammatory arthritis

Inflammatory arthritis is generally classified into seropositive and seronegative groups. These are based on the presence of rheumatoid factor, an immunoglobulin which reacts with gamma globulin, in the blood of the majority of patients with seropositive disease and in a small minority of patients with seronegative disease. The prototype seropositive form of arthritis is rheumatoid arthritis. Other members include the group of conditions labelled collagen vascular diseases, such as systemic lupus erythematosus, scleroderma, vasculitis, Sjogren’s syndrome. Only rheumatoid arthritis will be considered in this paper.

Among the seronegative inflammatory joint diseases is a group labelled spondyloarthritis. This condition is characterized by inflammatory disease of the joints of the back, both the sacroiliac joints and the apophyseal joints of the spine. Members of this group include ankylosing spondylitis, psoriatic arthritis, reactive arthritis, and arthritis of inflammatory bowel disease. While the prototype for this group is ankylosing spondylitis, psoriatic arthritis will also be discussed.

In addition to the presence of rheumatoid factor, there are extra-articular features which distinguish the seropositive from the seronegative forms of inflammatory arthritis.