Georgios Filippou, Laura Pezzoni, Emilio Filippucci, Sara K. Tedeschi, Tristan Pascart, Antonella Adinolfi, Edoardo Cipolletta, Charlotte Jauffret, Silvia Sirotti, Abhishek Abhishek, Daniel Albert, Mariano Andres, Herbert Baraf, Fabio Becce, Jessica Bertrand, Edyta Biernat‐Kałuża, Geraldo da Rocha Castelar-Pinheiro, Mats Dehlin, Cèsar Díaz‐Torné, Michael Doherty, Theodore R. Fields, John FitzGerald, Rada Gancheva, Rebecca Grainger, Nitin Kumar, Timothy Kwok, Augustin Latourte, Jean Liew, Worawit Louthrenoo, Péter Mandl, Tobias Manigold, Geraldine McCarthy, Ingrid Möller, Esperanza Naredo, Tuhina Neogi, Tom Niessink, Sébastien Ottaviani, Konstantinos Parperis, Fernando Perez‐ruiz, Carlos Pineda, Francesco Porta, Edward Roddy, Ann Rosenthal, Naomi Schlesinger, Francisca Sivera, Lisa Stamp, Vicky Tai, Anne-Kathrin Tausche, Lene Terslev, Patapong Towiwat, Till Uhlig, Florentin Ananu Vreju, Congcong Yin, Robert Terkeltaub, Nicola Dalbeth
OBJECTIVES: A systematic literature review (SLR) of publications from 2000 to 2022 identified terminology for calcium pyrophosphate crystal deposition (CPPD) and revealed substantial heterogeneity and poor adherence to recommendations. This study aimed to standardise CPPD terminology by developing an international consensus on labels and definitions. METHODS: Members of the Gout, Hyperuricemia and Crystal-Associated Disease Network (G-CAN) were invited by email to participate in a 3-round Delphi exercise. A steering committee identified key components of CPPD aetiology, pathophysiology, and clinical presentation among elements appearing in >10% of SLR papers, adding or removing items when scientifically justified. Participants selected preferred labels for each element. Respondents to the first round were invited to subsequent rounds. This paper reports the resulting G-CAN CPPD nomenclature. RESULTS: Consensus was reached for 'calcium pyrophosphate (CPP) crystal' and 'calcium pyrophosphate crystal deposition (CPPD)' to describe the deposition process. The unified term 'calcium pyrophosphate crystal deposition on imaging' was adopted across imaging modalities, whereas 'chondrocalcinosis' was redefined as conventional radiographic cartilage calcification consistent with CPPD. Four clinical manifestations were identified: 'acute CPP crystal arthritis' (with 'flare' for acute episodes), 'chronic CPP crystal arthritis', 'crowned dens syndrome', and 'osteoarthritis with CPPD'; the term 'pseudogout' received no support. The condition is now classified as 'asymptomatic CPPD' or 'CPPD disease' for symptomatic presentations. CONCLUSIONS: This G-CAN nomenclature is the first systematic effort to align CPPD terminology with contemporary biological and imaging evidence. By resolving longstanding ambiguities-particularly regarding 'chondrocalcinosis'-it provides a framework for consistent research definitions, clinical trial homogeneity, and improved patient care.