High prevalence of symptomatic enthesopathy of the shoulder in ankylosing spondylitis: Deltoid origin involvement constitutes a hallmark of disease

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Abstract
To examine the prevalence and characteristics of shoulder involvement in ankylosing spondylitis (AS). To analyze the sensitivity and specificity of shoulder lesions defined by magnetic resonance imaging (MRI) in patients with AS. Prevalence of shoulder involvement was ascertained by chart review of 400 AS patients. One hundred of these patients and 285 controls were selected for clinical evaluation. AS patients with a clinically defined shoulder disorder (n = 15) and a control group of 91 patients (94 shoulders) with nonspecific shoulder pain were studied with MRI. Fifty-four MRI-defined variables per shoulder were analyzed by 2 observers. A third cohort of patients with AS (n = 76) was prospectively evaluated by clinical exam for AS-specific shoulder lesions identified on MRI. Shoulder pain was recorded in 3.5% of patients by chart review. Shoulder involvement by clinical evaluation was noted in 24.7% of patients versus 14.2% of controls (odds ratio [OR] 8.17, 95% confidence interval [95% CI] 3.14–21.28, P < 0.001). Rotator cuff tendinitis was significantly more prevalent in patients (15.1%) than controls (3.5%; OR 8.17, 95% CI 2.66–25.14, P < 0.001). Acromioclavicular joint arthrosis was the most common lesion observed in AS shoulders (94%), although specificity was low (32%). Bone marrow edema at any entheseal site was noted in significantly more AS shoulders (70.6%) than in control (19.1%) shoulders (P < 0.001, corrected P = 0.02). Erosion of the greater tuberosity with or without adjacent bone edema had the best combination of sensitivity (58–65%) and specificity (86–92%). Intense acromial entheseal edema at the deltoid origin was observed only in AS shoulders (41.2%; P < 0.001). Evaluation of a prospective cohort of patients with AS showed that 22.4% had rotator cuff enthesopathy. Shoulder lesions in AS are common and characterized clinically by rotator cuff tendinitis and on MRI by intense bone edema localized to the supraspinatus/greater tuberosity and deltoid/acromial entheses. Intense acromial bone edema at the deltoid origin is a hitherto undescribed and highly specific feature of AS. Enthesopathy of the rotator cuff is underrecognized in AS and should be incorporated into instruments measuring enthesitis.