Morphologic, dynamic and high-resolution microscopy MRI in early-onset spondyloarthritis finger dactylitis

Objective: Up to now, the pathophysiology of SpA dactylitis has not been entirely clarified. It is not clear which are the involved tissues and which is the primary lesion of the "sausage-like" digit. The aim of our study was to examine the finger structures in early-onset finger dactylitis using high-resolution microscopy MRI together with morphologic and dynamic MRI. Subjects and methods: In a 6-month period, 13 SpA patients (7 females and 6 males), mean age 54.07 years (range 37-73 years) and mean disease duration 7.07 years (range 1-44 years) with early-onset finger dactylitis (less than 3 months) were recruited. Nine patients had PsA, 3 HLA-B27-positive uSpA and 1 HLA-B27-negative uSpA. One patient had 2 dactylitis fingers. Ten healthy volunteers matched for age and sex with no personal and family history of SpA were enrolled. All dactylitis fingers and randomly selected fingers of the normal control subjects were imaged by morphologic, dynamic and high-resolution microscopy MRI. Results: We have found flexor tenosynovitis in all the 14 dactylitis fingers, joint synovitis in 5 and oedema in the finger soft tissue in 10. In 2 dactylitis fingers, there was oedema at the insertion of the joint capsule suggesting enthesitis. In 5 dactylitis fingers, there was only mild enhancement at the enthesis organ (collateral ligament, flexor and extensor tendons). Conclusions: Our MRI study on early-onset dactylitis demonstrates that flexor tenosynovitis, joint synovitis and oedema of the digit soft tissue are the predominant alterations visible in the early phase of evolution of dactylitis and that, therefore, enthesitis may not be considered the primary lesion of dactylitis.