Ultrasound in the Evaluation of Dactylitis and Enthesitis in Psoriatic Arthritis

Dactylitis is a clinical concept that corresponds to the swelling of the whole finger or toe giving a sausage appearance. Although it can be observed in different diseases, it is a distinctive clinical feature of psoriatic arthritis and is associated with a poor prognosis. Ultrasound has made it possible to improve our understanding of the pathogenesis of psoriatic arthritis dactylitis, identifying associated structural alterations, namely, flexor tenosynovitis, subcutaneous tissue edema, pulley inflammation with thickening and intra-pulley Doppler signals, extensor paratenonitis, synovitis, pericapsular bone formation, and flexor enthesitis. Given its complexity, a consensus has yet to be reached on an ultrasound-based definition of dactylitis. In addition, enthesitis is one of the characteristic features of spondyloartritis. Enthesitis, like dactylitis, is among the clinical manifestations in the Assessment of SpondyloArthritis international Society classification criteria for both axial and peripheral spondyloartritis and is a key feature for classifying psoriatic arthritis with the Classification criteria for Psoriatic Arthritis criteria. Ultrasonography is a very useful tool for exploring the enthesis. We have a good sonographic definition, although ultrasound findings do not always allow us to differentiate between mechanical or inflammatory lesions. Elementary lesions that characterize enthesopathy are hypoechogenicity at the enthesis, thickened enthesis, calcification/enthesophyte at enthesis, erosion at enthesis, and Doppler signal at enthesis. Different composite indices have been proposed in order to classify spond yloarthropathies. This article reviews the evaluation of dactylitis and enthesitis from the sonographic perspective.