Enthesitis

Enthesitis is one of the key manifestations of spondyloarthritis (SpA) including ankylosing spondylitis (AS) and psoriatic arthritis. Enthesitis can occur alone or in combination with peripheral arthritis, sacroiliitis, or spondylitis. The inflammatory process is typically located at the insertion of the enthesis or ligament to bone, often resulting in osteitis as well. Because of its anatomical and functional complexity the term ’enthesis organ’ has been coined. Biomechanical stress applied to the enthesis seems to play an important role for the occurrence of enthesitis in genetically predisposed individuals. Ultrasound imaging of peripheral entheses reveals enthesis abnormalities including entheseal calcification, bony erosion, or bony proliferation. Power Doppler signals demonstrating increased vascularization of inflamed entheses at the insertional site appear to be the most characteristic finding for enthesitis, yet study results are conflicting. Enthesitis-related osteitis and enthesitis at the spine is best visualized by MRI. Enthesitis may resolve spontaneously or may run a chronic course. Standard treatment includes local steroid injections, non-steroidal anti-inflammatory drugs (NSAIDs), and physical therapy. There is little evidence for the efficacy of disease-modifying antirheumatic drugs (DMARDs) in enthesitis. In contrast, anti-TNF agents and other biologics have proven efficacy, and their use in treatment-resistant enthesitis is recommended in the Assessment of SpondyloArthritis international Society (ASAS)/European League Against Rheumatism (EULAR) recommendations for the management of AS and axial SpA and in the EULAR recommendations for psoriatic arthritis.