[Assessment and course of 110 patients with mono-arthritis]

This is a follow up study of 110 patients referred to the hospital because of mono-arthritis of unknown etiology. Patients with mechanical synovitis and infectious arthritis have been excluded from this study initially. From a total of 110 patients (100%) a diagnosis could be made in 49 patients (44.6%), namely in 24 (21.8%) by the initial very thorough work up or by the repeated examinations during the follow up period in 25 patients (22.8%). In 61 patients (55.4%) the cause of the disease remained unknown despite extensive investigations and follow up controls for many years. Of these 61 cases three (2.7%) developed polyarthritis and six (5.5%) oligoarthritis still of unknown origin. The rest, namely 52 (47.2%) remained mono-arthritis and are called mono-arthritis of unknown origin ("Arthritis unbekannter Ursache"). 67% of these 52 patients with mono-arthritis of unknown origin went into complete remission after one year and 80% after two years. 13 patients (11.8%) of the 110 developed rheumatoid arthritis within one month up to three years. Arthroscopy was important in making some diagnosis initially. Twelve patients had relief of symptoms after arthroscopy, ten of the group with mono-arthritis of unknown origin. 19 patients claimed that the initiating factor was a trauma to the joint.