Data from recent studies, using synovial biopsies of patients with FS, have shown a chronic presence of immune cells (mast cells, macrophages, T and B lymphocytes), as well as inflammatory mediators including cytokines, such as interleukins (IL)-1β, IL-6, IL-8, and tumor necrosis factor-alpha (TNF-α) (22), and matrix metalloproteinases (MMPs) (23) in the affected shoulder. Here, IL1B is linked to Feingold syndrome.