Tissue inflammation signatures point towards resolution in adhesive capsulitis

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Sir, Adhesive capsulitis (frozen shoulder) is a remarkable example of a severe, yet self-limiting, inflammatory and fibrotic condition affecting the shoulder joint capsule. Patients experience pain and restricted shoulder motion for up to 3 years, severely limiting activities and disrupting quality of life [1]. The disease mechanisms are poorly understood and there are no truly effective therapies for symptomatic patients. The pathological features of adhesive capsulitis are reported to include leucocyte and myeloid infiltration, fibroblast accumulation and increased vascularity [2]. However, the distinct inflammatory pathways and the phenotypes of tissue resident stromal cells active in disease remain to be identified, and may inform why the condition ultimately spontaneously resolves. In this case study, we use contrasting manifestations of established shoulder disease in similarly aged patients to advance understanding of why inflammation is frequently self-limiting in adhesive capsulitis but persists in shoulder rotator cuff tendon tears. We therefore investigated tissue inflammation signatures using previously validated markers [3, 4] to identify the phenotypes of macrophages and fibroblasts in samples from patients with adhesive capsulitis, comparing them with tissues from patients with shoulder rotator cuff tendon tears and with normal rotator cuff tendons. We also investigated if adhesive capsular tissues expressed proresolving receptors mediating resolution of inflammation.