Ultrasound of shoulder and knee improves the accuracy of the 2012 EULAR/ACR provisional classification criteria for polymyalgia rheumatica

OBJECTIVE: Recent studies suggest that the knee is frequently involved in PMR. In this study, we aimed to determine whether the US assessment of the shoulder and knee discriminates between PMR and other differential diagnoses and improves the accuracy of the 2012 EULAR/ACR provisional classification criteria for PMR. METHODS: We consecutively enrolled 81 untreated patients who received a diagnosis of PMR. These patients were divided into two groups based on the final diagnosis made at 1-year follow-up: PMR-definite group (n = 60) and PMR-mimic group (n = 21). We also enrolled age/sex-matched untreated RA patients with shoulder pain from an independent cohort (RA group, n = 60). All patients underwent comprehensive US assessment of the shoulder and knee for synovitis, bursitis, tenosynovitis, tendinitis and ligament inflammation at baseline. RESULTS: US scores for tenosynovitis, tendinitis and ligament inflammation better discriminated the PMR-definite group from the PMR-mimic and RA groups than do those for synovitis or bursitis. Among logistic regression models to identify US variables that were associated with the PMR-definite group, the best fitted model included two US variables: the bilateral involvement of the shoulder (long head of biceps, supraspinatus or subscapularis tendon) and the bilateral involvement of the knee (popliteus tendon or medial or lateral collateral ligament). Incorporating these two items into the 2012 EULAR/ACR provisional classification criteria numerically increased the accuracy to classify the PMR-definite group. CONCLUSION: US assessment of the tendon/ligament-related lesions in the shoulder and knee may improve the accuracy of the 2012 EULAR/ACR provisional classification criteria for PMR.