Reliability and Diagnostic Accuracy of Radiography for the Diagnosis of Calcium Pyrophosphate Deposition: Performance of the Novel Definitions Developed by an International Multidisciplinary Working Group

Intra-Articular Mineralization on Computerized Tomography of the Knee and Risk of Cartilage Damage: The Multicenter Osteoarthritis Study

OBJECTIVE

Intra-articular (IA) mineralization may contribute to osteoarthritis (OA) structural progression. We studied the association of IA mineralization on knee computed tomography (CT) with cartilage damage worsening on knee magnetic resonance imaging (MRI), with a focus on location- and tissue-specific effects.

METHODS

Participants from the Multicenter Osteoarthritis Study with knee CT and MRI scans were included. Presence of IA mineralization on CT was defined as a Boston University Calcium Knee Score >0 anywhere in the knee. Cartilage worsening on MRI was defined as any increase in the MRI OA Knee Score, including incident damage. We evaluated the association of whole-knee, compartment-specific (ie, medial or lateral), and subregion-specific (ie, location-matched) IA mineralization at baseline with cartilage worsening at two years' follow-up in the corresponding locations using binomial regression with generalized estimating equations, adjusting for age, sex, and body mass index (BMI).

RESULTS

We included 1,673 participants (mean age 60 years, 56% female, mean BMI 29). Nine percent had any IA mineralization in the knee, and 47.4% had any cartilage worsening on follow-up. Mineralization of any tissue in the knee, regardless of location, was not associated with MRI cartilage worsening. However, cartilage mineralization was associated with 1.39 (95% confidence interval 1.04-1.88) times higher risk of cartilage worsening in the same compartment, with similar results in subregion-specific analysis.

CONCLUSION

CT-detected IA mineralization in the cartilage was associated with higher risk of MRI cartilage worsening in the same compartment and subregion over two years. These findings suggest potential localized, tissue-specific effects of IA mineralization on cartilage pathology in knee OA.

2023 EULAR recommendations on imaging in diagnosis and management of crystal-induced arthropathies in clinical practice

OBJECTIVE

To formulate evidence-based recommendations and overarching principles on the use of imaging in the clinical management of crystal-induced arthropathies (CiAs).

METHODS

An international task force of 25 rheumatologists, radiologists, methodologists, healthcare professionals and patient research partners from 11 countries was formed according to the EULAR standard operating procedures. Fourteen key questions on the role of imaging in the most common forms of CiA were generated. The CiA assessed included gout, calcium pyrophosphate deposition disease and basic calcium phosphate deposition disease. Imaging modalities included conventional radiography, ultrasound, CT and MRI. Experts applied research evidence obtained from four systematic literature reviews using MEDLINE, EMBASE and CENTRAL. Task force members provided level of agreement (LoA) anonymously by using a Numerical Rating Scale from 0 to 10.

RESULTS

Five overarching principles and 10 recommendations were developed encompassing the role of imaging in various aspects of patient management: making a diagnosis of CiA, monitoring inflammation and damage, predicting outcome, response to treatment, guided interventions and patient education. Overall, the LoA for the recommendations was high (8.46-9.92).

CONCLUSIONS

These are the first recommendations that encompass the major forms of CiA and guide the use of common imaging modalities in this disease group in clinical practice.

High frequency of BCP, but less CPP crystal-mediated calcification in cartilage and synovial membrane of osteoarthritis patients

OBJECTIVE

Ectopic articular calcification is a common phenomenon of osteoarthritic joints, and closely related to disease progression. Identification of the involved calcium crystal types represents an important topic in research and clinical practice. Difficulties in accurate detection and crystal type identification have led to inconsistent data on the prevalence and spatial distribution of Basic calcium phosphate (BCP) and calcium pyrophosphate (CPP) deposition.

METHOD

Combining multiple imaging methods including conventional radiography, histology and Raman spectroscopy, this study provides a comprehensive analysis of BCP and CPP-based calcification, its frequency and distribution in cartilage and synovial membrane samples of 92 osteoarthritis patients undergoing knee replacement surgery.

RESULTS

Conventional radiography showed calcifications in 35% of patients. Von Kossa staining detected calcified deposits in 88% and 57% of cartilage and synovial samples, respectively. BCP crystals presented as brittle deposits on top of the cartilage surface or embedded in synovial tissue. CPP deposits appeared as larger granular needle-shaped clusters or dense circular pockets below the cartilage surface or within synovial tissue. Spectroscopic analysis detected BCP crystals in 75% of cartilage and 43% of synovial samples. CPP deposition was only detected in 18% of cartilage and 15% of synovial samples, often coinciding with BCP deposits.

CONCLUSION

BCP is the predominant crystal type in calcified cartilage and synovium while CPP deposition is rare, often coinciding with BCP. Distinct and qualitative information on BCP and CPP deposits in joint tissues gives rise to the speculation that different disease entities are involved that might need different treatment strategies.

Describing calcium pyrophosphate deposition: undoing the tower of Babel!

PURPOSE OF REVIEW

In 1977, McCarty astutely observed, 'The variety of names suggested for the condition associated with deposits of calcium pyrophosphate dihydrate crystals is exceeded only by the variations of its clinical presentation'. Fast forward to 2024, a standardized nomenclature for calcium pyrophosphate deposition (CPPD) is still lacking. This review aims to delineate the challenges in characterizing CPPD through nomenclature and imaging.

RECENT FINDINGS

Despite the effort of nomenclature standardization in 2011 by the EULAR, confusion persists in the literature and clinical practice, with pseudo-forms and obscure abbreviations. The Gout, Hyperuricemia and Crystal-Associated Disease Network (G-CAN) has launched a project to redefine CPPD nomenclature and formulate a user-friendly language for effective communication with patients and other stakeholders. Additionally, recent advancements in imaging, have shed light on various aspects of the disorder.

SUMMARY

Almost 60 years from the first description of a clinical manifestation related to calcium pyrophosphate crystals, a common language describing the disorder is still lacking. A redefined CPPD nomenclature, together with lay-friendly terminology, would significantly contribute to the uniformity of CPPD research, enhance public understanding and awareness and improve doctor-patient communication and therefore disease outcomes. Imaging can provide deep insights into CPPD elements, promoting comprehension of this disorder.

[First classification criteria for diseases caused by calcium pyrophosphate deposition (CPPD)-Translation, explanation and assessment]

AIM

For diseases caused by calcium pyrophosphate deposition (CPPD), validated classification criteria were previously lacking. In this article the recently developed and validated classification criteria are translated, explained, and assessed.

METHODS

In recent years a multinational research group developed classification criteria for CPPD disease with the support by the European Alliance of Associations for Rheumatology (EULAR) and the American College of Rheumatology (ACR), following an established method. The developed criteria were finally validated in an independent cohort. The translation and annotation of the new first classification criteria were carried out in an iterative procedure in consensus with the authors.

RESULTS

The presence of a crowned dens syndrome or calcium pyrophosphate crystals in the synovial fluid in patients with pain, swelling or sensitivity of the joints (entry criterion) is sufficient for the classification as CPPD disease, where the symptoms cannot be completely explained by another rheumatic disease (exclusion criterion). If these symptoms are not present, a count of more than 56 points based on weighted criteria comprised of clinical features and the results of laboratory and imaging investigations can be included for classification as a CPPD disease. These criteria had a sensitivity of 92.2% and a specificity of 87.9% in the derivation cohorts (190 CPPD cases and 148 mimics), whereas the sensitivity was 99.2% and the specificity 92.5% in the validation cohorts (251 CPPD cases and 162 mimics).

CONCLUSION

The ACR/EULAR classification criteria 2023 of a CPPD disease will facilitate clinical research in this field. The use in the clinical routine will show how practical the criteria are.

Synthesis of tetraphenylethylene-based small molecular sensor for the selective "turn-on" detection of pyrophosphoric acid in the aqueous solution

Pyrophosphoric acid (PPi) is a crucial indicator for monitoring adenosine triphosphate hydrolysis processes, and abnormal PPi levels in the human body seriously threaten human health. Thus the efficient detection of the concentration of PPi in the aqueous solution is important and urgent. This paper described the successful synthesis of a tetraphenylethylene (TPE) derivative, named as TPE-4B, which contained four chelate pyridinium groups exhibiting aggregation-induced emission characteristics. TPE-4B was explicitly developed for the selective and sensitive fluorescence detection of PPi in aqueous solutions, showing a fluorescence "turn-on" response, and the detection limit was 65 nM. The four chelate pyridinium moieties of TPE-4B exhibited robust electrostatic interactions and binding capacity towards PPi, leading to the formation of aggregations, which was confirmed by zeta potential, dynamic light scattering, and scanning electron microscopy. Compared with free TPE-4B in the aqueous solution, the zeta potential of aggregations decreased from 20.7 to 4.2 mV, the average diameter increased from 155 to 403 nm, and the morphology transformed from porous nanostructures into a block-like format. Leveraging these properties, TPE-4B is a promising candidate for a "turn-on" fluorescence sensor designed to detect PPi in the aqueous solution.

Relation of Intra-Articular Mineralization to Knee Pain in Knee Osteoarthritis: A Longitudinal Analysis in the MOST Study

OBJECTIVE

Intra-articular (IA) calcium crystal deposition is common in knee osteoarthritis (OA), but of unclear significance. It is possible that low-grade, crystal-related inflammation may contribute to knee pain. We examined the longitudinal relation of computed tomography (CT)-detected IA mineralization to the development of knee pain.

METHODS

We used data from the National Institutes of Health-funded longitudinal Multicenter Osteoarthritis Study. Participants had knee radiographs and bilateral knee CTs at baseline, and pain assessments every 8 months for 2 years. CT images were scored using the Boston University Calcium Knee Score. We longitudinally examined the relation of CT-detected IA mineralization to the risk of frequent knee pain (FKP), intermittent or constant knee pain worsening, and pain severity worsening using generalized linear mixed-effects models.

RESULTS

We included 2,093 participants (mean age 61 years, 57% women, mean body mass index 28.8 kg/m2 ). Overall, 10.2% of knees had IA mineralization. The presence of any IA mineralization in the cartilage was associated with 2.0 times higher odds of having FKP (95% confidence interval [CI] 1.38-2.78) and 1.86 times more frequent intermittent or constant pain (95% CI 1.20-2.78), with similar results seen for the presence of any IA mineralization in the meniscus or joint capsule. A higher burden of IA mineralization anywhere within the knee was associated with a higher odds of all pain outcomes (odds ratio ranged from 2.14 to 2.21).

CONCLUSION

CT-detected IA mineralization was associated with risk of having more frequent, persistent, and worsening knee pain over 2 years. Targeting IA mineralization may have therapeutic potential for pain improvement in knee OA.

The 2023 ACR/EULAR Classification Criteria for Calcium Pyrophosphate Deposition Disease

OBJECTIVE

Calcium pyrophosphate deposition (CPPD) disease is prevalent and has diverse presentations, but there are no validated classification criteria for this symptomatic arthritis. The American College of Rheumatology (ACR) and EULAR have developed the first-ever validated classification criteria for symptomatic CPPD disease.

METHODS

Supported by the ACR and EULAR, a multinational group of investigators followed established methodology to develop these disease classification criteria. The group generated lists of candidate items and refined their definitions, collected de-identified patient profiles, evaluated strengths of associations between candidate items and CPPD disease, developed a classification criteria framework, and used multi-criterion decision analysis to define criteria weights and a classification threshold score. The criteria were validated in an independent cohort.

RESULTS

Among patients with joint pain, swelling, or tenderness (entry criterion) whose symptoms are not fully explained by an alternative disease (exclusion criterion), the presence of crowned dens syndrome or calcium pyrophosphate crystals in synovial fluid are sufficient to classify a patient as having CPPD disease. In the absence of these findings, a score >56 points using weighted criteria, comprising clinical features, associated metabolic disorders, and results of laboratory and imaging investigations, can be used to classify as CPPD disease. These criteria had a sensitivity of 92.2% and specificity of 87.9% in the derivation cohort (190 CPPD cases, 148 mimickers), whereas sensitivity was 99.2% and specificity was 92.5% in the validation cohort (251 CPPD cases, 162 mimickers).

CONCLUSION

The 2023 ACR/EULAR CPPD disease classification criteria have excellent performance characteristics and will facilitate research in this field.

The 2023 ACR/EULAR classification criteria for calcium pyrophosphate deposition disease

OBJECTIVE

Calcium pyrophosphate deposition (CPPD) disease is prevalent and has diverse presentations, but there are no validated classification criteria for this symptomatic arthritis. The American College of Rheumatology (ACR) and EULAR have developed the first-ever validated classification criteria for symptomatic CPPD disease.

METHODS

Supported by the ACR and EULAR, a multinational group of investigators followed established methodology to develop these disease classification criteria. The group generated lists of candidate items and refined their definitions, collected de-identified patient profiles, evaluated strengths of associations between candidate items and CPPD disease, developed a classification criteria framework, and used multi-criterion decision analysis to define criteria weights and a classification threshold score. The criteria were validated in an independent cohort.

RESULTS

Among patients with joint pain, swelling, or tenderness (entry criterion) whose symptoms are not fully explained by an alternative disease (exclusion criterion), the presence of crowned dens syndrome or calcium pyrophosphate crystals in synovial fluid are sufficient to classify a patient as having CPPD disease. In the absence of these findings, a score>56 points using weighted criteria, comprising clinical features, associated metabolic disorders, and results of laboratory and imaging investigations, can be used to classify as CPPD disease. These criteria had a sensitivity of 92.2% and specificity of 87.9% in the derivation cohort (190 CPPD cases, 148 mimickers), whereas sensitivity was 99.2% and specificity was 92.5% in the validation cohort (251 CPPD cases, 162 mimickers).

CONCLUSION

The 2023 ACR/EULAR CPPD disease classification criteria have excellent performance characteristics and will facilitate research in this field.

Evaluating the safety and short-term equivalence of colchicine versus prednisone in older patients with acute calcium pyrophosphate crystal arthritis (COLCHICORT): an open-label, multicentre, randomised trial

BACKGROUND

Acute calcium pyrophosphate crystal arthritis causes intense joint pain mainly affecting older people. Because guidance and evidence remain scarce, management of this disease relies on expert opinion. We therefore aimed to compare the safety and short-term equivalence of low-dose colchicine with oral prednisone in older patients with acute calcium pyrophosphate crystal arthritis.

METHODS

We did an open-label, multicentre, randomised, trial (COLCHICORT) at six hospitals in Paris and northern France. We enrolled patients who were admitted to hospital who were 65 years or older and who presented with acute calcium pyrophosphate crystal arthritis with a symptom duration of less than 36 h. Diagnosis of calcium pyrophosphate crystal arthritis was made by the identification of calcium pyrophosphate crystals on synovial fluid analysis or typical clinical presentation (onset of joint pain and swelling). Key exclusion criteria included absence of calcium pyrophosphate crystals on synovial fluid analysis or a history of gout. Participants were randomly allocated (1:1), using a centralised electronic treatment group allocation module, to receive either colchicine 1·5 mg on day 1 and 1 mg on day 2 (ie, the colchicine group) or oral prednisone 30 mg on days 1 and 2 (ie, the prednisone group). The primary outcome was change in joint pain (measured by visual analogue scale [VAS] from 0 mm to 100 mm) at 24 h. Equivalence was determined whether the 95% CI of the between-group difference at 24 h was within the -13 mm to +13 mm margin in the per-protocol analysis. Adverse events were recorded using the National Cancer Institute Common Terminology Criteria for Adverse Events (version 4.0). This trial is completed and is registered with ClinicalTrials.gov, NCT03128905.

FINDINGS

Between Feb 5, 2018, and May 7, 2022, 111 patients who were admitted to hospital were randomly assigned (57 [51%] to the colchicine group and 54 [49%] to the prednisone group). 95 (86%) of 111 patients were included in the per-protocol analysis (49 [52%] in the colchicine group and 46 [48%] in the prednisone group). The median age was 88·0 years (IQR 82·0-91·0) and 69 (73%) of 95 participants were women and 26 (27%) were men. Acute calcium pyrophosphate crystal arthritis affected mainly the knee in 46 (48%) of 95 participants, the wrist in 19 (20%), and the ankle in 12 (13%). Pain VAS at baseline was 68 mm (SD 17). At 24 h, change in pain VAS was -36 mm (SD 32) in the colchicine group and -38 mm (SD 23) in the prednisone group. The between-group difference in change in pain VAS at 24 h was -1 mm (95% CI -12 to 10), showing equivalence between the two drugs. In the colchicine group, 12 (22%) of 55 patients had diarrhoea, one (2%) had hypertension, and none had hyperglycaemia. In the prednisone group, three (6%) of 54 had diarrhoea, six (11%) had hypertension, and three (6%) had hyperglycaemia. No deaths occurred in the colchicine group; two deaths occurred in the prednisone group, which were deemed unrelated to prednisone (one due to infectious valvular endocarditis leading to heart failure, and one due to a stroke).

INTERPRETATION

Colchicine and prednisone exhibit equivalent short-term efficacy for the treatment of acute calcium pyrophosphate crystal arthritis, with different safety profiles in the older population.

FUNDING

French Inter-regional Hospital Program of Clinical Research.

Development and validation of an OMERACT ultrasound scoring system for the extent of calcium pyrophosphate crystal deposition at the joint level and patient level

BACKGROUND

The Calcium Pyrophosphate Deposition (CPPD) subgroup of the Outcome Measures in Rheumatology (OMERACT) Ultrasound working group was established to validate ultrasound as an outcome measure instrument for CPPD, and in 2017 has developed and validated standardised definitions for elementary lesions for the detection of calcium pyrophosphate crystals in joints. The aim of this study was to develop and evaluate the reliability of a consensus-based ultrasound scoring system for CPPD extent, representing the next phase in the OMERACT methodology.

METHODS

In this study the novel scoring system for CPPD was developed through a stepwise process, following an established OMERACT ultrasound methodology. Following a previous systematic review to gather available evidence on existing scoring systems for CPPD, the novel scoring system was developed through a Delphi survey based on the expert opinion of the members of the OMERACT Ultrasound working group-CPPD subgroup. The reliability of the scoring system was then tested on a web-based and patient-based exercise. Intra-reader and inter-reader reliability of the new scoring system was assessed using weighted Light's κ coefficients.

FINDINGS

The four-grade semiquantitative scoring system consisted of: grade 0 (no findings consistent with CPPD), grade 1 (≤3 single spots or 1 small deposit), grade 2 (>3 single spots or >1 small deposit or ≥1 larger deposit occupying ≤50% of the structure under examination in the reference image-ie, the scanning view with the highest grade of depositions), and grade 3 (deposits that occupy more than 50% of the structure under examination in the reference image). The score should be applied to the knee (menisci and hyaline cartilage) and the triangular fibrocartilage complex of the wrist. The intra-reader and inter-reader reliabilities on static images were almost perfect (κ 0·90 [95% CI 0·79-1·00] and κ 0·84 [0·79-0·88]), and on the eight patients recruited (four [50%] female and four [50%] male) were substantial (κ 0·72 [95% CI 0·47 to 0·96] and 0·66 [0·61 to 0·71]).

INTERPRETATION

This OMERACT ultrasound scoring system for CPPD was reliable on both static images and patients. The scoring system might be a valuable tool for ensuring valid and comparable results in clinical trials and could help monitor the extent of crystal deposition in patients with CPPD in clinical practice.

FUNDING

The Italian Ministry of Health - Ricerca Corrente.

Which are the most frequently involved peripheral joints in calcium pyrophosphate crystal deposition at imaging? A systematic literature review and meta-analysis by the OMERACT ultrasound – CPPD subgroup

Objectives

To identify the prevalence of calcium pyrophosphate crystal deposition (CPPD) using ultrasound and conventional radiology at peripheral joints in patients with suspected or definite CPPD.

Methods

A systematic literature search was performed in PubMed and Embase using pre-defined search strategies from inception to April 2021 to identify studies that evaluated conventional radiology and ultrasound in detecting CPPD at peripheral joints, including definite or suspected CPPD [Research question 1 (RQ1) and Research Question 2 (RQ2), respectively]. For the meta-analysis, the first, second, and third sub-analysis included studies with the knee, and knee or wrist as the index joint for CPPD (without restrictions on the reference standard) and synovial fluid analysis or histology as a reference standard (without restrictions on the index joint), respectively.

Results

One-thousand eight hundred and twenty-seven manuscripts were identified, of which 94 articles were finally included. Twenty-two and seventy-two papers were included in RQ1 and RQ2, respectively. The knee had the highest prevalence for RQ1 and RQ2 by both conventional radiology and ultrasound, followed by the wrist with the highest prevalence for RQ1. The hand had the lowest CPPD prevalence. The third sub-analysis showed a higher CPPD prevalence on ultrasound than conventional radiology at the knee (only data available).

Conclusion

Among all peripheral joints, the knees and wrists could be regarded as the target joints for CPPD detection by imaging. Furthermore, ultrasound seems to detect a higher number of calcium pyrophosphate deposits than conventional radiology, even when using a more restrictive reference standard.