Should oligoarthritis be reclassified? Ultrasound reveals a high prevalence of subclinical disease

Objective: To determine the prevalence of subclinical synovitis using ultrasound (US) imaging of both painful and asymptomatic joints, in patients with early (<12 months), untreated oligoarthritis (5 joints).

Methods: Eighty patients underwent a detailed clinical assessment by two physicians. All painful joints were identified, which were immediately scanned by a sonographer. In the last 40 patients, an additional standard group of joints was scanned to establish the prevalence of synovitis in asymptomatic joints.

Results: In 80 patients, 644 painful joints (with and without clinical synovitis) were identified and each underwent a US assessment. Of these joints, 185 had clinical synovitis, of which, US detected synovitis in only 79% (147/185). In the other 38 joints US demonstrated tenosynovitis instead of synovitis in 12 joints and possible, but not definite, synovitis in 11 joints. Fifteen joints were, however, normal on US. In 459 joints that were not clinically synovitic, US detected synovitis in 33% (150/459). In 64% (51/80) of patients, US detected synovitis in more joints than clinical examination and in 36% (29/80) of patients, US detected a polyarthritis (>6 joints). Of the 826 asymptomatic (non-painful) joints scanned, 13% (107/826) had US detected synovitis.

Conclusion: Sonography detected more synovitis than clinical examination in patients with oligoarthritis. In almost two thirds of patients there was evidence of subclinical disease while one third could be reclassified as polyarticular. These findings suggest that a definition of oligoarthritis based purely on clinical findings may be inappropriate, which may have important implications for disease management.