Enthesitis in psoriatic arthritis: a distinct domain and an early marker in the spectrum of spondyloarthritis

Background and objectives. Enthesitis is a hallmark of psoriatic arthritis (PsA) and may represent an early pathogenic event in its development. This study aimed to assess the prevalence, severity, and distribution of enthesitis in PsA compared to rheumatoid arthritis (RA), cutaneous psoriasis without arthritis (PsO), and ankylosing spondylitis (AS), as well as its variation across PsA clinical subtypes. Materials and methods. We conducted a mixed (retrospective–prospective), monocentric study including 256 PsA, 147 RA, 171 PsO, and 111 AS patients evaluated at a tertiary rheumatology center (2015–2025). Enthesitis was assessed clinically using LEI and SPARCC indices, and confirmed by musculoskeletal ultrasound (MSUS) and MRI in selected cases. Results. Enthesitis was present in 50.0% of PsA patients, significantly more frequent than in RA (4.8%) or PsO (15.2%), and comparable to AS (60.4%). SPARCC and LEI scores were significantly higher in PsA vs. RA/PsO (p<0.001). Enthesitis was most common in axial and mutilating PsA subtypes and correlated with dactylitis, nail disease, and elevated CRP. MSUS identified subclinical enthesitis in ~10% of PsA and ~20% of PsO patients. Most frequently affected sites were Achilles and plantar fascia insertions. Conclusions. Enthesitis is a frequent and early feature of PsA, with diagnostic and prognostic value. Its presence supports PsA diagnosis and may precede clinical arthritis. Systematic assessment of entheses, including imaging in psoriasis patients with vague musculoskeletal symptoms, could improve early PsA detection and management.