HLA B27 related 'unclassifiable ' seronegative spondyloarthropathies

SUMMARY Twenty-five patients (22 males and 3 females) are described who had 'unclassifiable' seronegative peripheral arthritis affecting mainly the large joints of the lower limbs with other typical features of spondyloarthropathies such as heel pain, low back pain, and mucosal ulcers. But their disorders could not be diagnosed as any specific spondyloarthropathy such as ankylosing spondylitis, Reiter's disease, etc. The mean age of onset of disease was 21 *4 years and 60 % of them had mono- or oligoarthritis; 60 % had arthritis of only lower limb joints. Knee, ankle, and hip joints were most commonly involved, often asymmetrically (mean degree of asymmetry = 0.28). Mini-mal radiographic sacroiliitis was present in 4 patients, though 13 had low back pain. HLA B27 antigen was detected in 21 (84%) of these patients and only 5 9 % of 118 controls (relative risk 83). In addition to these 25 patients there were 4 others whose only symptom was severe bilateral heel pain: 3 of them were positive for HLA B27. Seronegative polyarthritis is a heterogeneous clinical entity frequently seen in rheumatological practice. The condition in most of the patients may ultimately evolve into seropositive erosive rheumatoid arthriti