Synovitis occurs in some clinically normal and asymptomatic joints in patients with early arthritis.

Objective: To determine if clinically asymptomatic knee joints in patients with recent onset arthritis reveal histological evidence of synovitis.

Methods: As part of a prospective study of patients with synovitis of less than one year duration, we performed blind needle biopsies on the knees of 20 patients who had synovitis elsewhere but no symptoms or detectable swelling or tenderness of the biopsied joint.

Results: Histologic evidence of synovitis was observed in 11 knees (55%). All patients with synovitis had evidence of synovial lining cell hyperplasia, increased vascularity, and lymphocytic infiltrates. Five of 6 patients with rheumatoid arthritis (RA) and 5 of 8 with undifferentiated arthritis had histological evidence of synovitis, but none of the 5 with reactive arthritis (ReA) had synovitis in the asymptomatic joints. Histologic evidence of synovitis persisted in some after clinical resolution of previous pain and swelling, while it occurred in others with no history of previous involvement of that knee.

Conclusion: Even asymptomatic joints in patients with RA and undifferentiated arthritis of recent onset reveal histologic signs of synovitis. The earliest changes may occur before symptoms. Histologic changes also persist after resolution of previous early symptoms. Evidence of inflammation was not present in asymptomatic joints in our 5 patients diagnosed with ReA.