Development of Classification Criteria

• Persistent inflammatory arthritis is defined by joint swelling, pain, and/or warmth in one or more joints that persists.
• A typical episode is defined as an acute onset or worsening of joint pain and swelling/warmth that resolves, regardless of treatment.
• Conditions like hereditary hemochromatosis, primary hyperparathyroidism, hypomagnesemia, Gitelman syndrome, hypophosphatasia, and familial history of CPPD disease should be considered.
• Synovial fluid analysis should be conducted by an expert using compensated polarized light microscopy for crystal identification.
• Imaging of a symptomatic peripheral joint (CR, US, CT, or DECT) is required if criteria are not met.
• Imaging evidence includes calcification of fibrocartilage or hyaline cartilage, not the synovial membrane, joint capsule, or tendon.
• Classification criteria and weights are presented in Table 2.
• The CEC agreed that imaging of a symptomatic peripheral joint is necessary when sufficient criteria are not met.
• A web-based calculator is available at https://bblinks.live/acrclassification-criteria-for-cppd-disease.
• The percent agreement of Steering Committee members for classifying patients for a research study ranged from 53% to 57% (Figure 3).
• Among 190 definite cases in the derivation cohort, 130 met sufficient criteria and 60 remained for scoring.
• These 60 cases had an area under the curve (AUC) of 0.95 (95% CI 0.93-0.98).
• A threshold score of >56 was chosen to maximize specificity and sensitivity.
• When the entire classification criteria system was applied, the threshold score had a sensitivity of 97.8% and specificity of 87.9%.
• Examples of borderline cases included a single episode of acute inflammatory arthritis in the wrist and a single episode in the knee with other conditions present.
• Among 251 definite cases in the validation cohort, 186 met sufficient criteria and 65 remained for scoring.
• The threshold score of >56 had a sensitivity and specificity of 96.5% and 92.5%, respectively, in this subgroup.
• Classification criteria performance in the derivation and validation cohorts demonstrated high sensitivity (99.2%) and specificity (92.5%).
• The percentage of patient profiles classified as CPPD disease increased with the submitting clinician's rating of CPPD.

§ Persistent inflammatory arthritis is defined by ongoing joint swelling with pain and/or warmth in one or more joints, with a typical episode being an acute worsening of joint pain and swelling that resolves regardless of treatment.

§ Certain conditions like hereditary hemochromatosis, primary hyperparathyroidism, hypomagnesemia, Gitelman syndrome, hypophosphatasia, and familial history of CPPD disease should be considered in the diagnosis.

§ Synovial fluid analysis should be done by an expert to identify crystals using compensated polarized light microscopy.

§ Imaging of at least one symptomatic peripheral joint is required for consideration. Imaging evidence includes calcification of fibrocartilage or hyaline cartilage.

§ The American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) classification criteria for CPPD disease include entry, exclusion, sufficient, and scored criteria.

§ A threshold score of >56 was chosen, as it maximizes specificity at 87.9% while retaining a high sensitivity of 92.2%.

§ The classification criteria have good performance, with sensitivity and specificity of 96.5% and 92.5%, respectively, in a subgroup of the validation cohort.

§ The classification framework, including entry, exclusion, sufficient criteria, and the threshold score of >56, had a sensitivity of 99.2% and specificity of 92.5% among all definite cases and definite mimickers in the validation cohort.

§ The percentage of cases classified as CPPD disease increases with the submitting clinician’s rating of CPPD.

§ The study, published in Annals of the Rheumatic Diseases, aimed to develop evidence-based classification criteria for CPPD disease using a multidisciplinary approach.