Enthesitis in psoriatic arthritis (Part 2): imaging

Enthesitis is a hallmark finding in PsA and may predate the onset of synovitis. Clinical examination of enthesitis provides no structural information, relies on eliciting tenderness at entheseal sites and may not be sensitive or specific. Soft tissue imaging techniques such as musculoskeletal ultrasound and MRI can depict ultrastructural and inflammatory changes. Although these imaging techniques are complimentary, ultrasound can image superficial entheses with high fidelity and examine vascularity with the use of Doppler but cannot image subchondral bone. MRI depicts bone and can visualize bone marrow edema as well as soft tissue edema. However, due to short relaxation times, entheseal structures are not easily differentiated. There has been increasing recognition of biomechanical confounding, especially since the majority of the entheses examined are in the lower extremity. Imaging entheseal indices are being developed to minimize the effect of body weight and activity. In the following article, contemporary concepts of entheses in relation to imaging will be reviewed as well as important confounders in assessing entheseal alterations. The role and limitations of imaging techniques will be discussed.