The relationship between HLA-B27 positive peripheral arthritis and sacroiliitis.

HLA typing for B27 antigen is a helpful diagnostic aid in the classification of peripheral arthritis patients (especially young patients) who are rheumatoid factor negative. We studied 109 patients with seronegative peripheral arthritis belonging to various clinical categories; 23% proved to be B27 positive in comparison to 7% of normal controls. In spite of a paucity of spinal manifestations there was a high prevalence of sacroiliitis (83%) in the B27 positive peripheral arthritis patients as opposed to only 21% in those without B27 antigen. HLA-B27 typing and radiographs of the sacroiliac joints are important differential tests.