Detection of enthesitis in children with enthesitis-related arthritis: dolorimetry compared to ultrasonography

Abstract

Objective: To evaluate the distribution of enthesitis and the accuracy of physical examination with a dolorimeter for the detection of enthesitis in children, using ultrasound (US) assessment as the reference standard.

Methods: We performed a prospective cross-sectional study of 30 patients with enthesitis-related arthritis (ERA) and 30 control subjects. The following tendon insertion sites were assessed by standardized physical examination with a dolorimeter and US: common extensor on the lateral humeral epicondyle, common flexor on the medial humeral epicondyle, quadriceps at the superior patella, patellar ligament at the inferior patella, Achilles, and plantar fascia at the calcaneus.

Results: Abnormal findings on US were detected most commonly at the insertion of the quadriceps (30% [18 of 60 sites]), common extensor (12% [7 of 60]), and Achilles (10% [6 of 60]) tendons. The intrarater reliability of US (kappa statistic) was 0.78 (95% confidence interval [95% CI] 0.63-0.93), and the interrater reliability was 0.81 (95% CI 0.67-0.95). Tenderness as detected by standardized dolorimeter examination had poor positive predictive value for US-confirmed enthesitis. In comparison to controls, patients with ERA reported more pain and had lower pain thresholds at every site, including control sites (P < 0.001 for all comparisons). The interrater reliability of dolorimeter examination for detection of enthesitis was low (κ = 0.49 [95% CI 0.33-0.65]).

Conclusion: Compared to US, standardized dolorimeter examination for the detection of enthesitis in children has poor accuracy and reliability. The decreased pain threshold of ERA patients likely contributed to the limited accuracy of the physical examination findings. Further research regarding the utility of US for identifying enthesitis at diagnosis of juvenile idiopathic arthritis, accurately predicting disease progression, and guiding therapeutic decisions is warranted.

Figure 1. Ultrasound examination

Ultrasound examination of the common extensor tendon insertion at the lateral elbow using a Philips IU22 machine with a high-frequency linear array 12 MHz transducer. Power Doppler was assessed in long and transverse imaging planes. A) Images were acquired with the elbow in mild flexion and the forearm pronated. B) An image from the gray-scale evaluation shows the thickness of the tendon, as delineated by the arrowheads. LE= lateral epicondyle, R= radial head. C) An image from the Doppler evaluation shows moderate vascularization. The red regions are increased power Doppler signals, which indicate increased vascularity.

Figure 2. Sites of enthesitis by ultrasound

Sites of US-defined enthesitis in ERA cases and controls, N (%). 60 entheses examined for each of the 6 sites. Enthesitis by US was defined as power Doppler (grade 2 or 3) at the cortical bone insertion, abnormal tendon appearance (loss of fibrillar pattern, regions of hypoechogenicity, or fusiform thickening) or structural abnormalities (calcification, enthesophytes, or erosions). Skeleton downloaded from Wikimedia commons. ERA= enthesitis related arthritis.