When can calcium pyrophosphate deposition disease be considered a polymyalgia rheumatica mimicking disease?

Introduction: Similarly to polymyalgia rheumatica (PMR), calcium pyrophosphate deposition (CPPD) disease is common among older people. Calcium pyrophosphate deposition can present in several forms, including proximal manifestations associated with raised inflammatory markers. Consequently, CPPD disease may be diagnosed as PMR. Recently, a European Alliance of Associations for Rheumatology and American College of Rheumatology (EULAR/ACR) collaborative initiative proposed new classification criteria for symptomatic CPPD disease. This review paper aimed to discuss when CPPD disease could be considered a PMR-mimicking disease in the light of these criteria. Material and methods: We performed a non-systematic literature search on PubMed, regardless of the language. Abstracts submitted at conferences or from non-peer-reviewed sources were not included. Results: The prevalence of CPPD among patients categorized as having PMR supported the inclusion of CPPD among the PMR-like diseases. However, CPPD disease was not diagnosed among the 169 subjects in the non-PMR comparison group in the 2012 EULAR/ACR classification proposal for PMR. According to the 2023 EULAR/ACR study design for symptomatic CPPD, within the 148 definite mimickers forming the derivation cohort, 6 were affected by PMR; only one was affected by PMR within the 162 definite mimickers forming the validation cohort. Finally, in all the studies on this topic, no patient with PMR and CPPD was reported to have a late diagnosis of giant cell arteritis, at least within the term of follow-up of each study. Conclusions: The relationship between PMR and CPPD should be reviewed in light of the 2023 EULAR/ACR classification criteria for symptomatic CPPD disease. Applying these 2023 criteria, we were able to identify three possible scenarios in patients categorized as having PMR according to the 2012 EULAR/ACR criteria: 1) polymyalgic manifestations in patients with already diagnosed CPPD disease (PMR/CPPD or pseudo-PMR CPPD pattern); 2) polymyalgic manifestations categorized as PMR in patients with concurrent diagnosed CPPD disease (symptomatic CPPD with overlapping PMR); 3) polymyalgic manifestations categorized as PMR in patients with undiagnosed chronic CPPD disease (PMR with concurrent undiagnosed CPPD). Further studies are additionally required to confirm the possibility that the PMR/CPPD subset may be a non-vasculitic pattern of disease.