Undifferentiated spondyloarthropathy in Korea: focusing on peripheral arthritis.

Undifferentiated spondyloarthropathy (USpA) includes the forms that do not meet criteria for the established categories of spondyloarthropathy. The clinical spectrum of USpA is therefore wide and few studies have been published on USpA, especially peripheral arthritis. A total of 107 patients fulfilling the European Spondyloarthropathy Study Group criteria for SpA were studied retrospectively by a chart review and interview by a rheumatologist. Peripheral arthritis, excluding hip and shoulder involvement, occurred in 97 of the 107 patients (91%). Joint involvement tended to be monoarticular or pauciarticular, and most frequently developed in peripheral joints including the knee and ankle. Among the 97 patients with peripheral arthritis, only 37 (35%) had a persistent arthritis. HLA-B27 was detected in 80 patients (78%). Peripheral arthritis was found in the lower extremities regardless of symmetry or asymmetry and tended to run a benign course with only a few patients having persistent arthritis.