Undiagnosed chronic monarthritis. Clinical and evolutionary profile

The features and clinical course in 38 patients (25 women, 13 men) who had chronic monarthritis of undetermined origin (UCM) were surveyed over a mean followup period of 24.6 months. At the end of the study, the cause was still unknown in 26 patients (65.7%). In 10 patients, symptoms resolved spontaneously. In the remaining 12 patients, a diagnosis became apparent after a mean period of 17.2 months; diagnoses included spondylarthritis (6 patients), rheumatoid arthritis (3 patients), osteoarthritis (1 patient), erosive arthropathy (1 patient), and glomus tumor (1 patient). Patients in whom a diagnosis emerged were more likely to have positive findings on the following studies: rheumatoid factor (2 of 12); HLA-B27 typing (6 of 11); bone scan, positive over the sacroiliac joint or non-index joint(s) (4 of 6); and roentgenograms of the sacroiliac joint (3 of 8). Findings of these same studies were notably negative in the subgroup of patients with UCM that spontaneously resolved.