Background In the last decade, ultrasonography (US) demonstrated to be a useful tool for the diagnosis of calcium pyrophosphate dihydrate deposition disease (CPPD) but the heterogeneity of the criteria used for calcium pyrophosphate crystal (CPP) US detection remains the main limit of this technique regarding reproducibility.
Objectives The aim of this study was to define, on the basis of a systematic literature review and experts' opinion, the criteria for US identification of CPP deposits.
Methods The first step of this study was the systematic literature review, aimed to identify all the studies regarding US and CPPD and to retrieve the definitions used for the description of the CPP deposits. In the second step, a rheumatologist expert in musculoskeletal ultrasound (MSUS) drew up a first group of definitions for US CPPD identification based on the results of the literature research.
In the third step, the propositions were evaluated by a task force composed by 7 members: 4 senior rheumatologists experienced in MSUS, 1 senior rheumatologist expert in imaging, 1 radiologist expert in musculoskeletal imaging and 1 junior rheumatologist with 3 years' experience in MSUS. This step was carried out with the Delphi technique. The consensus was considered obtained for a score greater than or equal to 7.
Results Based on the results of the systematic review, we created five groups of definitions. The first four groups were based on the structure under examination: fibrocartilage, hyaline cartilage, tendons and synovial fluid. For each group we defined: echogenity, shape, localization and behavior during dynamic scanning of CPP deposits. The fifth group contained the most important recommendations and tricks for a correct identification of deposits as described in the literature and also based on the experience of the panel of experts. Three Delphi rounds were needed in order to reach a consensus on each preposition
Final definitions for US identification of CPP deposits are summarized in the Table 1.
Conclusions This is the first attempt, to our knowledge, carried out by a group of experts in order to define US criteria for CPPD identification. The use of these criteria could improve the reproducibility of US among sonographers and promote a greater diffusion of ultrasound as a diagnostic tool for the diagnosis of CPPD.
Disclosure of Interest None declared