Summary

Enthesitis is a term that refers to inflammation at tendon, ligament, or joint capsule insertions. The entheses are increasinlgly considered to be the primary site of joint inflammation in the spondyloarthropathies including psoriatic arthritis (PsA). Great advances have occurred in the understanding of enthesopathy, which has resulted in a better understanding of the etiopathogenesis of PsA. Enthesitis is difficult to assess on both clinical examination and on imaging because of the overlap in features between mechanical, degenerative, and inflammatory pathologies. Ultrasonography frequently detects entheseal abnormalities in patients with psoriasis, despite the absence of clinical symptoms of arthropathy and the longitudinal value of such lesions for PsA prediction remains unknown. The role of magnetic resonance imaging (MRI) in the assessment and monitoring of enthesitis is not fully agreed on but it is clearly superior for the assessment of spinal polyenthesitis and for diffuse peri-enthseal osteitis that can occur anywhere in the skeleton. Nuclear medicine, including conventional positron-emission tomography (PET) and high-resolution PET scan (hrPET), is more of a research tool for enthesitis and can, for example, help distinguish between PsA and osteoarthritis. Entheseal abnormalities are common in osteoarthritis, which creates diagnostic difficulty from PsA. Entheseal changes, especially on imaging, may also occur in rheumatoid arthritis (RA) and likely reflect the extension of the inflammatory process from the adjacent synovium. The nail is anatomically anchored to the skeleton via a mini-enthesis network. An association between ultrasonography determined distal interphalageal joint (DIP) extensor tendon enthesopathy and clinical nail disease was found, which highlights the pivotal role of the enthesis in this PsA risk factor. This review summarizes the relevant insights and implication of imaging for enthesitis, primarily in PsA but also in other arthropathies.