Long-term outcome of undifferentiated spondylarthropathy

Undifferentiated spondylarthropathy is one of the common disease subsets in the group of so-called seronegative spondarthritides. It is not exactly known how often it differentiates into ankylosing spondylitis or other well-defined disease subsets over time. The present study was designed to find out the long-term outcome in this subset. Thirty-five patients diagnosed with undifferentiated spondylarthropathy between January 1987 and December 1988 were recruited. Twenty-two (63%) of them were available for detailed assessment I I years after the original diagnosis. Their baseline characteristics did not differ from those of the original cohort of 35 patients and were as follows: male:female ratio 19:3, median age of onset 17 years (range 8-39), and median duration of disease 8 months (range 4-24). Clinical features were enthesitis (45%) and inflammatory pain in the back (100%), buttock (77%), hip (64%), shoulder (18%), knee (82%), ankle (77%), and hand and wrists (50%). There was no restriction in spinal movement. Family history was positive in two cases. Radiologically, the only finding was grade I sacroiliitis in 17 patients (77%). Human leukocyte antigen (HLA)-B27 was positive in all. Functionally, all were in class 1. During follow-up, one patient developed psoriatic skin lesions after 9 years. Uveitis developed in four patients (18%). After a median follow-up of I I years, 15 (68%) had ankylosing spondylitis, one developed psoriatic arthritis, four remained undifferentiated, and two had natural remission. Functionally, 19 patients (86%) were in class I and three (14%) were in class III. No patient had bamboo spine, but three underwent total hip replacement. Thus, a majority of patients (68%) with undifferentiated spondylarthropathy gradually developed ankylosing spondylitis of mild severity.