Spondyloarthropathy

Spondyloarthropathies are inflammatory joint diseases associated with the MHC class I molecule HLA-B27. The term seronegative spondylarthropathy is used by medical practitioners because this set of conditions may mimic rheumatoid diseases such as rheumatoid arthritis, but serological (blood) tests are typically negative for rheumatoid factor (RhF).

Subgroups (with increased HLA-B27 frequency) are:

• ankylosing spondylitis Caucasians (AS, 92%),
• ankylosing spondylitis African-Americans (AS, 50%),
• reactive arthritis (Reiter's syndrome) (RS, 60-80%),
• enteropathic arthritis associated with inflammatory bowel disease (IBD, 60%),
• Psoriatic arthritis (60%),
• isolated acute anterior uveitis (AAU, iritis or iridocyclitis, 50%), and
• undifferentiated SpA (USpA, 20-25%).

Whipple disease and Behçet disease may also be linked to HLA-B27, as may undifferentiated spondyloarthropathy.

• Note: One of the causes of erosive or destructive spondyloarthropathy is tertiary hyperparathyroidism.