Which ultrasound lesions contribute to dactylitis in psoriatic arthritis and their reliability in a clinical setting

Objectives To explore the frequency of ultrasound elementary lesions in dactylitis in psoriatic arthritis (PsA), and the reliability of scoring these lesions in a clinical setting. Methods In 31 patients with PsA and clinical dactylitis, ultrasound assessment of the affected finger or toe was performed using greyscale and color Doppler mode. One examiner scanned all patients and a second examiner scanned 10 patients for inter-reader reliability. For each digit, the following lesions were evaluated: subcutaneous edema; soft tissue thickening; synovitis of the digital joints; tenosynovitis of the flexor tendon; enthesitis at the deep flexor tendon and the extensor tendon entheses; and paratenonitis of the extensor tendon. A dactylitis sum-score was calculated. Findings in clinically tender and non-tender digits were compared. Results The most frequent lesions were soft tissue thickening (81%) and subcutaneous edema (74%) followed by synovitis (56-68%) and flexor tenosynovitis (52%). Color Doppler was most frequently found subcutaneously (55%) and around the flexor tendons (45%). All lesions were typically found in combinations, most commonly subcutaneous edema and synovitis (71%), subcutaneous edema and flexor tenosynovitis (52%), and all three in combination (52%). Tender digits had a higher dactylitis sum-score and numerically higher prevalence of most lesions than non-tender digits. Intra- and inter-reader agreements were moderate to excellent, though lower for few components of digital enthesitis, especially hypoechogenicity. Conclusion Dactylitis in PsA appears to encompass several lesions, most often subcutaneous changes combined with synovitis and/or flexor tenosynovitis. Reliability of scoring established ultrasound lesions of dactylitis in a clinical setting is moderate-excellent.