Outcome domains reported in calcium pyrophosphate deposition studies:A scoping review by the OMERACT CPPD working group

Introduction Although calcium pyrophosphate deposition (CPPD) is common, there are no validated outcome domains and/or measurements for CPPD studies. The aim of this work was to identify domains that have been reported in prior clinical studies in CPPD, to inform the development of a core set of domains for CPPD studies. Methods We performed a scoping literature review for clinical studies in CPPD, searching in Medline (via PubMed), EMBASE, and Cochrane Central Register of Controlled Trials (CENTRAL) databases; published from January 1, 1946 to January 7, 2020. All reported outcomes and study design data were extracted and mapped to the core areas and domains as defined by the OMERACT Filter 2.1.The protocol was registered on PROSPERO (CRD: 42019137075; 09-07-2019). Findings There were 112 papers identified, comprising of 109 observational studies and three randomized controlled trials. Most studies reported clinical presentations of OA with CPPD or acute CPP crystal arthritis. Outcomes that mapped to 22 domains were identified; the most frequently reported measures mapped to the following domains/sub-domains: imaging (joint damage on imaging tests - 59 studies; joint calcification on imaging tests - 28 studies), joint pain (26 studies), response to treatment (23 studies), side effects of treatment (15 studies), inflammation in the joint fluid or blood (ESR or C-reactive protein - 12 studies; synovial fluid markers - 4 studies; other blood markers - 2 studies), overall function (14 studies), joint swelling (12 studies) and range of joint movement (10 studies). Very few studies mapped to domains related to life impact, societal/resource use or longevity. Conclusion There is substantial variability in outcomes reported in CPPD studies. Outcomes that map to imaging manifestations, joint pain and response to treatment domains are most often reported.