Pseudogout, chondrocalcinosis, CPPD et al: crystal clear… or clear as mud?–The time has come to reconsider the nomenclature of calcium pyrophosphate deposition

Scientific interest in calcium pyrophosphate deposition (CPPD) has been limited by several challenges. These include difficulties in diagnosis due to diverse clinical presentations, the lack of classification criteria, the absence of standardised diagnostic modalities, underrecognition in clinical care, and, most significantly, the lack of evidence-based treatments. Consequently, CPPD was often regarded as the ‘poor cousin’ of gout. Fortunately, in recent years, CPPD has garnered increased attention from the rheumatology community. Milestones such as the first American College of Rheumatology/European Alliance of Association for Rheumatology classification criteria, the European Alliance of Association for Rheumatology recommendations for the use of imaging in clinical practice, validated OMERACT ultrasound definitions and scoring system, and the OMERACT core domain sets for CPPD have significantly advanced the field. Yet, unresolved issues regarding CPPD nomenclature hold back advancement in both research and clinical practice. The terminology surrounding CPPD remains inconsistent in the scientific literature, with numerous terms and acronyms used to describe the condition and its manifestations. For example, many ‘pseudosyndromes’ (eg, pseudogout) and purely radiographic descriptors (eg, chondrocalcinosis) are still commonly used by clinicians and researchers interchangeably, as either the name of the condition or one of its clinical or radiographic manifestations. This lack of standardisation complicates communication among health care professionals, researchers, and between doctors and patients, creating insurmountable barriers to effective care and research advances. In this viewpoint, we highlight the value of standardised terminology, drawing parallels with other rheumatic diseases. We aimed to explore the historical evolution of CPPD nomenclature, assess the impact of previous standardisation efforts, and propose a possible way for a common language.