SPP1 and rheumatoid arthritis: An in-depth understanding of the differences and similarities of the dysregulation of the Wnt pathway and of other serum biomarkers such as serum osteopontin (32) in inflammatory diseases (i.e., PMR, RA, Giant Cell Arteritis, etc.)and on the dysregulation of the RANKL/OPG ratio may prove useful in the future and contribute to improve the management of these conditions.