[Mono-arthritis of uncertain etiology--a follow-up study].

78 patients in whom the cause of a monoarticular arthritis remained unclear after an initial workup were contacted for a follow-up interview (and an additional clinical examination in 64 cases) after 6 to 11 years (mean 8 years). The mean age at the onset of symptoms was 39 years, with 51% of the patients presenting in the range between 20 and 40 years. There was a slight male preponderance (56%). Large joints, mainly the knee, and less often the wrist, ankle or hip, were affected in 79%. Finger, toe and other small joints were involved in only 21%. During the course of the disease 14% of the cases developed arthritis in other joints. At the time of follow-up an etiologic or nosologic diagnosis was possible only in 5%: 1 infectious Pneumococcus pneumoniae arthritis, 1 Lyme arthritis (Borrelia burgdorferi), 1 gouty arthritis and 1 erosive seronegative rheumatoid arthritis. 95% of all cases remained unclear. However, 91% of all patients became free of symptoms after 6 years. The remaining patients (9%) suffered from arthralgia of undetermined origin (n = 5), from nonclassified destructive coxitis with consecutive development of unclear gonarthritis (n = 1), or from erosive seronegative rheumatoid arthritis (n = 1). 10 patients (13%) underwent a total of 16 invasive procedures related to their arthritis, such as synoviorthesis, synovectomy or arthrodesis. The result of the erythrocyte sedimentation rate had no influence on the outcome. The following conclusions are offered: monoarticular arthritis initially should prompt a thorough investigation in order to exclude infectious or metabolic etiologies for their destructive potential.(ABSTRACT TRUNCATED AT 250 WORDS)