Enthesitis of proximal insertion of the deltoid in the course of seronegative spondyloarthritis. An atypical enthesitis that can mime impingement syndrome

Objective: to study the frequence of deltoideal proximal insertion enthesitis (DPIE) in patients affected with spondyloarthritis (SpA) and to evaluate its clinical, sonographic and radiological characteristics. Methods: a retrospective study of clinical, sonographic and radiological examinations of the shoulders of 100 symptomatic consecutive outpatients with SpA, compared to 4 groups of control patients: 100 with Rheumatoid Arthritis, 100 with Osteoarthritis, 100 with Painful Shoulder, and 50 with shoulders undamaged by local pathological processes. Results: the frequence of DPIE in the course of SpA was 9%. DPIE appears most frequently in Psoriatic Arthritis (PsA) (17%, 7/41). DPIE does not appear to be related to the sex or the age of the patient. The clinical signs and symptoms are similar to those of an impingement syndrome. Sonography reveals thickening and hypoechogenicity of the enthesis, associated or not to the subchondral osseous rearrangement and enthesophytosis. Radiology only reveals the enthesophytosis in the later stages. Conclusions: DPIE can determine shoulder pain in the course of SpA, and in particular in PsA. The clinical manifestations of DPIE are very similar to those of an impingement syndrome; sonography can differentiate the two conditions.