Gout, Hyperuricemia and Crystal-Associated Disease Network (G-CAN) consensus statement regarding labels and definitions for disease elements in calcium pyrophosphate crystal deposition (CPPD).

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.