HLA-B27 and involvement of sacroiliac joints in rheumatoid arthritis.

The frequency of radiographic signs of sacroiliac joint involvement (greater than or equal to 2 and greater than or equal to 3 according to the New York criteria) was significantly higher in 28 HLA-B27 positive patients with classical seropositive rheumatoid arthritis (RA), than in 28 B27 negative RA controls. The B27 positive RA patients had more subcutaneous nodules (p less than 0.01), worse functional class (p less than 0.05), and higher levels of erythrocyte sedimentation rate (ESR) (p less than 0.05) and haptoglobin (p less than 0.05). Sacroiliitis, independent of HLA-B27, was associated with higher levels of ESR (p less than 0.05), and with a higher frequency of positive ANA test (p less than 0.05). It is neither related to the functional class nor to the duration of the disease.