Clinical and histologic observations of monoarthritis. Anticipation of its progression to rheumatoid arthritis.

Synovial biopsies were performed on 84 patients with monoarticular synovitis from 1960 to 1984. Twenty-seven (32%) of 84 patients were pathologically differentiated; however, the other patients remained classified as nonspecific monoarthritic. Follow-up studies of nonspecific monoarthritis ranging from five to 25 years (average, 15 years) were carried out in 34 patients. Five patients (15%) disclosed polyarticular involvement and were diagnosed as having classic rheumatoid arthritis (RA) within five years after initial biopsy (RA group). In the remainder (non-RA group), 19 patients recovered completely and nine of ten patients complained of a slight degree of joint involvement. A good prognosis was observed in younger patients and in those who showed minimal histologic changes in the synovium. Initial laboratory examinations, including a white cell count, erythrocyte sedimentation rate, C-reactive protein, and agglutination test, did not show any differences between the RA and the non-RA groups. To determine predicting factors for RA, a comparative histologic study of the initial specimens was performed. Specimens from the RA group showed a predominant appearance of lymphoid aggregates, high endothelial postcapillary venules, and proliferative plasma cell infiltration. These histologic features suggest the future appearance of RA; therefore, careful observation and early treatment should be considered for these patients.