Abstract
Objective
Due to protean presentations, poor sensitivity of radiographs and variable reliability of synovial fluid analysis, diagnosis of Calcium pyrophosphate deposition disease (CPPD) is a challenge. This study addressed the diagnostic performance of musculoskeletal ultrasound (MSK-USG) in identifying CPPD features in hyaline cartilage, fibrocartilage, tendon, and synovial fluid. We compared ultrasound findings in CPPD to those in osteoarthritis (OA) and gout and healthy control.
Materials & methods
In this retrospective exploratory study, MSK-USG performed between February 2022 and July 2023 were reviewed. Patients retrospectively fulfilled the ACR/ EULAR classification criteria 2023 (score ≥ 56) were included (n = 16). Clinical phenotypes included acute CPP arthritis (44%), CPPD with OA (44%), and chronic CPP arthritis (12%). Ultrasound images were evaluated at common CPPD target sites: hyaline cartilage and fibrocartilage of the knee, wrist triangular fibrocartilage, metacarpophalangeal joints, joint capsules, tendons, and synovial membranes. Ultrasound images of CPPD cases were compared to those of OA, gout, and healthy controls. Sensitivity, specificity, and predictive values were calculated for Ultrasound features.
Results
Compared to healthy controls, Ultrasound features showed a sensitivity of 94.12% (CI: 71.31–99.85), specificity of 100% (CI: 86.77–100), positive predictive value of 100%, and negative predictive value of 99.59% in diagnosing CPPD. Ultrasound findings in hyaline cartilage showed a sensitivity & a specificity of 100% each. Fibrocartilage involvement showed a sensitivity of 93.75% and specificity of 86.67%. Whereas these figures were lowest for tendons with sensitivity of 12.5% (CI: 1.55–38.35) and specificity of 86.67% (CI: 69.28–96.24), respectively. Compared to OA, sensitivity and specificity were 100% and 93.75%, respectively. Specificity was lower when compared to gout (40%).
Conclusions
MSK-USG demonstrated high diagnostic accuracy in identifying CPPD, especially in hyaline cartilage and fibrocartilage. While these findings support the use of Ultrasound as an adjunctive diagnostic tool, particularly in distinguishing CPPD from OA, the small sample size and retrospective design limit generalizability. Prospective studies with larger cohorts and crystal-confirmed cases are needed for validation.
Keywords: CPPD, Bangladesh, Musculoskeletal ultrasonography
Key points
Due to limited data and expertise in detecting CPPD crystals in synovial fluid, patients are often misdiagnosed with conditions such as seronegative rheumatoid arthritis or osteoarthritis. This study aims to highlight the presence of CPPD in Bangladesh and other South Asian countries.
MSK-USG plays a crucial role in the diagnosis of CPPD.
This study will enhance physicians’ understanding of ultrasound findings associated with CPPD.
Introduction
Calcium pyrophosphate deposition disease (CPPD) is the third most common inflammatory arthritis amongst certain populations characterized by the deposition of calcium pyrophosphate (CPP) crystals mainly in the articular tissues, frequently in the fibrocartilage and hyaline cartilage [1–3].
Research in CPPD is always hindmost and no data exist on prevalence of CPPD from South Asia including Bangladesh in published literature. The heterogeneity of presentations, lack of sensitivity of radiographic imaging in diagnosis, variable credence of synovial fluid analysis makes the diagnosis of CPPD laborious [2, 4].
However, with the successful use of musculoskeletal ultrasound (MSK-USG) in the recent years, the new ACR-EULAR classification criteria 2023 for CPPD incorporated ultrasound in it [2, 4–6].
This exploratory study aimed to assess the diagnostic accuracy of MSK-USG in detecting CPPD features in hyaline cartilage, fibrocartilage, tendons, and synovial membrane in a Bangladeshi cohort. Findings were compared with those in age and sex-matched patients with osteoarthritis (OA), gout, and healthy controls.
Materials & methods
Patients & study design
In this retrospective exploratory study, all the MSK-USG scans performed from February 2022 to July 2023 in the rheumatology unit were retrieved and reviewed.
All patients retrospectively fulfilled the ACR/EULAR classification criteria 2023 for CPPD i.e., scoring more than 56 points were included [2]. Exclusion criteria were age < 18 years, a history of intraarticular corticosteroid injection within 3 months, or alternative diagnoses like rheumatoid arthritis (RA).
Clinical and laboratory data of the patients meeting the entry criteria as defined above (n = 16), were recorded from the electronic medical record of the hospital. The ultrasonographic features were largely retrieved from the ultrasound database of the department, except a few documented prospectively, more so of the controls. To distinguish sonographic features of CPPD, ultrasound images were compared with that of 30 healthy controls, 16 patients with OA and 5 patients with gout. Clinical diagnosis of OA was based on ACR criteria [7] and exclusion criteria were history of acute inflammatory arthritis, Prior identification of CPP crystals or urate crystals in synovial fluid, coexisting autoimmune diseases (e.g., RA, SLE). For gout group, patients were selected who fulfill 2015 ACR/EULAR classification criteria for gout [8]. Exclusion criteria were concomitant diagnosis or clinical suspicion of CPPD and absence of typical clinical features.
Clinical assessment
Acute CPP arthritis: The rapid development of severe joint pain, swelling and tenderness that reaches its maximum within 6–24 h, especially with overlying erythema, is highly suggestive of acute crystal inflammation though not specific for acute CPP crystal arthritis [3].
Chronic CPP crystal inflammatory arthritis presents as chronic oligoarthritis or polyarthritis with inflammatory symptoms and signs and occasional systemic symptoms (with elevation of C-reactive protein (CRP) and Erythrocyte sedimentation rate (ESR); this may also include superimposed flares typical of crystal inflammation [3].
Ultrasound assessment
The scans of all the patients who fulfilled the ACR-EULAR classification criteria for CPPD were retrospectively evaluated independently by one rheumatologist and a radiologist. Both sonographers—the rheumatologist and radiologist—had formal training in MSK-USG, including certified workshops. Each had more than five years of experience performing MSK-USG, ensuring standardized acquisition and interpretation of ultrasound images.
To overcome the challenges of disagreement between the 2 sonographers, the Interobserver agreement was assessed by the ‘κ’appa coefficient.
Ultrasonographic images were obtained by a Samsung RS85 prestige machine equipped with a 14 − 7 MHz linear transducer.
The cartilage of the metacarpal heads from the second to the fifth finger was scanned longitudinally on the dorsal side of the hand with the fingers in maximum flexion. The cartilage of the femoral condyles was observed by transverse anterior scans with the knee in maximum flexion and posterior scans with the leg extended. The triangular ligament of the carpus was studied with multiplanar scans, rotating the probe around the ulnar compartment of the wrist [9]. The medial and lateral menisci of the knee were examined with multiplanar scans with the knee flexed at 30–45 and completely extended [9].
Definitions of ultrasound imaging features of CPPD in the various structures imaged are described as per validated published literature and mentioned under the following paragraphs [10].
CPP crystal deposition in fibrocartilage or hyaline cartilage (Figs. 1 and 2)
Fig. 1.
Longitudinal scan of medial compartment showing hyperechoic deposits in medial compartment
Fig. 2.
Knee joint transverse scan showing hyperechoic deposits within hyaline cartilage
Hyperechoic deposits of variable shape and size, localized within the fibrocartilage or hyaline cartilage structure, that remain fixed or move along with the fibrocartilage/hyaline cartilage during dynamic assessment and do not create posterior shadowing.
Synovial membrane (Fig. 3)
Fig. 3.
Hyperechoic deposits in synovial membrane
hyperechoic deposits of variable shape and size, localized within the synovial membrane, that do not create posterior shadowing unless they reach large dimensions.
Joint capsule
hyperechoic deposits of variable shapes and sizes, localized within the capsule, that remain fixed and move along with the capsule during dynamic assessment and do not create posterior shadowing.
Tendon
hyperechoic, linear structures without posterior shadowing, localized within the tendon that remain fixed and move along with the tendon during dynamic assessment.
Statistical analysis
The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and the accuracy of the MSK-USG test for diagnosing patients with CPPD was calculated using the MedCalc web package [11] According to the MedCalc tool, the confidence intervals for sensitivity, specificity and accuracy are calculated using the exact Clopper-Pearson method. Additionally, the confidence intervals for the likelihood ratios are calculated using the & q Log method of Altman et al. 2000 [12].
The confidence intervals for the predictive values are calculated using the standard logit confidence intervals except when the predictive value is 0 or 100%, in which case a Clopper-Pearson confidence interval is reported [13].
For analysis, the disease prevalence used in this study is 7% for the CPPD vs. healthy control groups, 20% for the CPPD vs. OA group and 5% for the CPPD vs. gout group based on existing data.
Square Hospital ethical clearance committee approval was taken in prior for this study outlined as above. As this is retrospective study, the data were collected from electronic record. Human Ethics and Consent to Participate declarations: not applicable.
Results
Characteristics of the study population
Between February 2022 and July 2023, we found sixteen patients with CPPD retrospectively fulfilling the ACR-EULAR criteria 2023 from the electronic medical records of the hospital, of whom 15 (93.75%) were females. The mean age was 65.75 (SD ± 10.03) years. As controls, we assessed 30 healthy people, 16 cases with OA and 5 patients with Gout. The mean symptom duration prior to presentation as per hospital records was 24.37 (
21.66) days. Table 1 represents the demographic features of CPPD and control groups.
Table 1.
Demographic and clinical characteristics of study population
| CPPD n = 16 |
Healthy (control) n = 30 |
OA (control) n = 16 |
Gout (control) n = 5 |
|
|---|---|---|---|---|
| Number of patients | 16 | 30 | 16 | 5 |
| Sex (female: male) | 15:1 | 26:4 | 14:2 | 0:5 |
| Age, mean (SD) | 65.75 ± 10.03) | 65.75 ± 10.03 | 61 ± 5.68 | 64 ± 5.68 |
CPPD = calcium pyrophosphate deposition: OA = osteoarthritis
The clinical patterns of presentation: Acute CPP crystal arthritis and OA with CPPD, each constituted 44% of our cohort, while Chronic CPP crystal arthritis constituted only 12% of cases.
Ultrasound assessments
Compared to heathy controls, MSK-USG showed sensitivity in the diagnosis of CPPD as 94.12% (CI: 71.31–99.85) and Specificity 100% (CI: 86.77–100). Compared to osteoarthritis, MSK-USG showed sensitivity of 100% (CI: 79.41–100) & specificity of 93.75% (CI: 69.77–99.84); when compared to gout, the specificity was as low as 40% (CI: 5.27–85.34) & sensitivity was 100% (CI: 79.41–100). Table 2 represents the performance of MSK-USG in the diagnosis of CPPD.
Table 2.
Performance of MSK-USG for the diagnosis of CPP deposition disease
| CPPD (n-16) vs. healthy control (n = 30) | CPPD (n = 16) vs. OA (n-16) | CPPD (n = 16) vs. Gout (n = 5) | |
|---|---|---|---|
| Sensitivity | 94.12 (71.31–99.85) | 100 (79.41–100) | 100 (79.41–100) |
| Specificity | 100 (86.77–100) | 93.75 (69.77–99.84) | 40 (5.27–85.34) |
| Positive predictive value | 100 (79.48–100) | 80 (37.48–96.39) | 8.06 (4.11–15.25) |
| Negative predictive value | 99.59 (90.99–100) | 100 (78.2–100) | 100 (15.81–100) |
Values are the percentage (95% confidence interval). CPPD = calcium pyrophosphate deposition: OA = osteoarthritis
However, values were different across different structures. Ultrasound findings in hyaline cartilage showed 100% sensitivity and 100% specificity. Findings in tendon showed the lowest of the sensitivity, i.e., 12.5% (CI: 1.55–38.35) and findings in fibrocartilage showed the lowest specificity i.e. 86.67% (CI: 69.28–96.24) in our study. Table 3 lists the variations in the accuracies of performance by ultrasound assessment for CPPD across different structures.
Table 3.
Performance of MSK-USG in different site for the diagnosis of CPP deposition disease
| Sensitivity | Specificity | PPV | NPV | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CPPD vs. healthy control | CPPD vs. OA | CPPD vs. Gout | CPPD vs. healthy | CPPD vs. OA |
CPPD vs. Gout | CPPD vs. healthy | CPPD vs. OA | CPPD vs. Gout | CPPD vs. healthy | CPPD vs. OA | CPPD vs. Gout | |
| FC | 93.75 (69.77–99.84) | 93.75 (69.77–99.84) | 93.75 (69.77–99.84) | 86.67 (69.28–96.24) | 100 (79.41–100) | 60 (14.66–94.73) | 34.61 (17.40-57.07) | 100 (78.2–100) | 10.98 (4.02–26.66) | 99.46 (96.49–99.92) | 98.75 (86.84–100) | 99.45 (96-99.93) |
| HC | 100 (78.2–100) | 100 (78.2–100) | 100 (78.2–100) | 100 (88.43–100) | 93.75 (69.77–99.84) | 40 (5.27–85.34) | 100 (78.2–100) | 80 (37.48–96.39) | 8.06 (4.11–15.21) | 100 (88.43–100) | 100 (78.2–100) | 100 (15.81–100) |
| SM | 50 (24.65–75.35) | 50 (24.65–75.35) | 50 (24.65–75.35) | 100 (88.43–100) | 100 (79.41–100) | 80 (28.36–99.49) | 100 (63.06–100) | 100 (63.06–100) | 11.63 (2.09–44.82) | 96.37 (94.21–97.78) | 88.89 (83.05–92.89) | 96.82 (94.3-98.32) |
| JC | 25 (7.27–52.38) | 25 (7.27–52.38) | 25 (7.27–52.38) | 100 (88.43–100) | 100 (79.41–100) | 60 (14.66–94.73) | 100 (39.76–100) | 100 (39.76–100) | 3.18 (0.83–11.45) | 94.66 (93.03–95.92) | 84.21 (80.08–87.62) | 93.83 (87.56–97.07) |
| Tendon | 12.5 (1.55–38.35) | 12.5 (1.55–38.35) | 12.5 (1.55–38.35) | 93.33 (77.93–99.18) | 100 (79.4–100) | 60 (14.66–94.73) | 12.37 (2.14–47.64) | 100 (15.81–100) | 1.62 (0.3–8.13) | 93.41 (92-94.58) | 82.5 (65.01–93.58) | 92.87 (86.15–92.46) |
| Combined | 94.12 (71.31–99.85) | 100 (79.41–100) | 100 (7941 − 100) | 100 (86.77–100) | 93.75 (69.77–99.84) | 40 (5.27–85.34) | 100 (86.77–100) | 80 (37.48–96.39) | 8.06 (4.11–15.25) | 99.59 (90.99–100) | 100 (78.2–100) | 100 (25.81–100) |
PPV = positive predictive value: NPV-negative predictive value: FC = fibro cartilage: HC = hyaline cartilage: SM = synovial membrane: JC = joint capsule
All the structures were evaluated through MSK-USG as per the ultrasound components listed under the ACR-EULAR 2023 criteria for CPPD and these items were compared to healthy and disease controls. Ultrasound of tendons showed the lowest sensitivity of 12.5% and ultrasound of hyaline cartilage showed 100% sensitivity for CPPD. Calcifications in the meniscal fibrocartilage of the knee was seen in 4 healthy controls and tendon calcifications were observed in 2 healthy controls.
Synovial fluid analysis reports were available for 8 patients and none of them were found to be positive for crystals. Four of them were found to have raised WBC count 11,535 (± 18831) with predominantly neutrophils in the differential count of 60 (± 31) %.
ESR data was found for 7 patients and the mean was 54 (± 15) mm in first hour and C-reactive protein (CRP) was also raised at 36(± 24) mg/L.
Interobserver agreement
Agreement was assessed for lesion identification across all groups (CPPD, OA, gout, and healthy controls). Included exact agreement percentages and kappa coefficient (κ = 0.87).
Discussion
Literature reports CPPD as a relatively common disease amongst elderly persons in certain populations and it is known to be characterized by deposition of CPP crystals in joint and periarticular tissues [9]. [14], Aging is a major risk factor for CPPD, which was reconfirmed in our study given the mean age of 65 years in our cohort [3]. However, due to lack of appropriate diagnostic test, it is difficult to diagnose CPPD and the exact prevalence and incidence is not known in most countries including Bangladesh [9]. Due to difficulties in diagnosis, chronic CPPD are usually diagnosed as seronegative RA by most medical practitioners and, therefore, the 2011 EULAR recommendation proposed CPPD as a differential diagnosis of seronegative RA and chronic inflammatory arthritis in the elderly population [3, 15]. Moreover, radiography does not exclude the diagnosis of CPPD and low sensitivity of crystals in synovial fluid due to interobserver variability and due to several other obstacles like small crystal size, weak or absent positive birefringence, difficulties in aspiration of joint fluid especially from small joints emphasize the importance of doing MSK-USG for the diagnosis of CPPD [2, 16]. In this study, synovial fluid analysis (SFA) was done only in eight patients and none of them were positive for CPP crystal and failure of detection of crystals might be due to lack of expertise for detection of crystal as well. In addition, the ‘‘shedding theory’’ of CPP also explains the low sensitivity of detection of crystals, as they primarily form in articular tissues rather than shedding into synovial space following diverse stimuli. That means, CPPD could be present in joint tissue much before crystals could be detected in SFA; therefore, imaging technique like ultrasound could identify these crystals better in tissues as was found in our study [6].
In this study, high sensitivity and specificity strengthen the case for MSK-USG as a diagnostic modality of CPPD disease, which also echo 2023 ACR/ EULAR classification criteria that give a major weightage to ultrasound features for diagnosing CPPD disease. Imaging and clinical features or identification of CPPD crystals from synovial fluid was sufficient for classification of CPPD when these are present [2]. Compared to healthy controls, sensitivity of MSK-USG for diagnosing CPPD in our study was 94.12%, while it was 100% when compared to OA and gout. The specificity, however, were 100%, 93.75% and 40% respectively, compared to healthy control, OA, and gout; and this is consistent with other published literature [17]. Other studies, however, found varied metrics such as specificity of 77.1% and sensitivity of 74.4% by Lee KA et al. We found hyaline cartilage calcification with 100% sensitivity and 93.75% specificity, which is consistent with some studies. Better visualization by parapatellar view and presence of effusion can further increase the visualization of hyaline cartilage. This specific ultrasound finding has high specificity because of its ability to differentiate various forms of crystal arthropathies [4]. Out of our 16 cases, synovial effusion was present in 15 cases. In this study, fibrocartilage involvement (Fig. 1A) showed a little bit lower sensitivity of 93.75% than hyaline cartilage (Fig. 1B). Whereas, in some studies fibrocartilage involvement is seen more than any other structure and underlying pathogenic aspects do support this observation as CPP crystals first deposit on fibrocartilage and only at a later stage, they deposit in hyaline cartilage [6, 9, 18]. Varus knee alignment that generally determines a medial meniscus extrusion from the joint line, help ultrasound to access a larger portion of the meniscus allowing a better identification of CPP crystals [14]. But there are complexities in identifying crystals in fibrocartilage, as the ligaments crossing these structures are hyperechogenic resembling crystals and thereby, making it sometimes difficult to identify [6].
Tendon involvement showed 12.5% sensitivity with 93.3% specificity indicating late involvement of tendon structure in the natural course of CPPD [1].
This study showed high positive predictive value (PPV) both in comparison to healthy controls and diseased controls namely OA at 100% and 80%, respectively; however, in comparison to gout, the PPV was only 8.06%. This high PPV indicate, MSK-USG can be used as a routine test to diagnose CPPD; on the other hand, very high negative predictive value (NPPV), found in this study while comparing to healthy control (99.59%), as well as in comparison with OA (100%) indicate that MSK-USG can be used as screening test for CPPD.
Regarding clinical phenotypes, acute CPP arthritis and OA with CPPD constituted 44% each of the CPPD cases in our study, whereas chronic CPP arthritis constituted only 12% of our cases. CPPD with OA is a frequent manifestation and it is a difficult subtype to be diagnosed, as some grade of OA changes do co-exist in the same joint. However, CPPD with OA is associated with more inflammatory features and the main difference is presence of effusion and higher white cell count in synovial fluid [3, 6, 16]. Our study also demonstrated similar findings.
One of the major strengths of our study includes demonstration of diagnostic performance of MSK-USG alone as a diagnostic tool. All the images are evaluated by both radiologist and rheumatologist. Despite the small sample size, especially for the gout, and the absence of crystal confirmation through synovial fluid analysis or histopathology, our findings support the diagnostic utility of MSK-USG, in line with the 2023 ACR/EULAR classification criteria. These results highlight the potential of MSK-USG as a frontline imaging modality for CPPD diagnosis, especially in resource-constrained settings where crystal analysis is not routinely available.
Our study does have several limitations. Our sample size is small. Despite being diagnosed as CPPD disease according to ACR-EULAR criteria 2023, none of the cases was proven by positive crystal analysis and histopathological data. Without histopathological analysis, it may not be possible to detect the exact nature of calcifications visualized by MSK-USG, especially for differentiation between basic calcium phosphate (BCP) and CPP crystals [4, 19]. Also we applied the new ACR-EULAR criteria largely on a retrospective cohort, necessitating a prospective validation study to prove our point that ultrasonography alone is a highly effective method to diagnose CPPD.
In conclusion, this exploratory study demonstrates that MSK-USG is a valuable bedside tool with excellent sensitivity, specificity, and positive predictive value in the CPPD, particularly in distinguishing it from OA. Among the anatomical sites evaluated, hyaline cartilage and fibrocartilage calcification showed the highest diagnostic accuracy, reinforcing its role as a key sonographic feature of CPPD. In contrast, tendon involvement was infrequently detected and demonstrated the lowest sensitivity, suggesting its limited utility in early diagnosis. Larger, prospective studies incorporating crystal-proven cases are needed to validate these findings and to further define the diagnostic role of MSK-USG in CPPD diagnosis.
Acknowledgements
Department of radiology & imaging, Square hospitals LTD.
Abbreviations
- CPPD
Calcium pyrophosphate deposition disease
- OA
Osteoarthritis
- MSK-USG
Musculoskeletal ultrasound
- CPP
Calcium pyrophosphate
- PPV
Positive predictive value
- BCP
Basic calcium phosphate
- NPPV
Negative predictive value
- RA
Rheumatoid arthritis
- FC
Fibro cartilage
- HC
Hyaline cartilage
- SM
Synovial membrane
- JC
Joint capsule
- SFA
Synovial fluid analysis
Author contributions
FS: concept, data collection, write the manuscript JF: Imaging, data collection AMA: review the manuscript MRH: review the manuscript ZA: review the manuscript MIH: statistical analysis.
Funding
None.
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethics approval and consent to participate
Ethical approval was taken from Square Hospital ethical clearance committee Data were collected from electronic record. No consent from patient was required.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Lee KA, Lee SH, Kim HR. Diagnostic value of ultrasound in calcium pyrophosphate deposition disease of the knee joint. Osteoarthritis Cartilage. 2019;27(5):781–787. doi: 10.1016/j.joca.2018.11.013. Epub 2019 Feb 6. PMID: 30738145. [DOI] [PubMed]
- 2.Abhishek A, Tedeschi SK, Pascart T, Latourte A, Dalbeth N. etal. The 2023 ACR/EULAR classification criteria for calcium pyrophosphate deposition disease. Ann Rheum Dis 2023 Jul 26:ard-2023-224575. 10.1136/ard-2023-224575. Epub ahead of print. PMID: 37495237. [DOI] [PMC free article] [PubMed]
- 3.Zhang W, Doherty M, Bardin T, Barskova V, Guerne PA. European league against rheumatism recommendations for calcium pyrophosphate deposition. Part I: terminology and diagnosis. Ann Rheum Dis. 2011;70(4):563–70. Epub 2011 Jan 7. PMID: 21216817. [DOI] [PubMed] [Google Scholar]
- 4.Ottaviani S, Juge PA, Aubrun A, Palazzo E, Dieudé P. Sensitivity and reproducibility of ultrasonography in calcium pyrophosphate crystal deposition in knee cartilage: A Cross-sectional study. J Rheumatol. 2015;42(8):1511–3. 10.3899/jrheum.141067. Epub 2015 Jun 15. PMID: 26077407. [DOI] [PubMed] [Google Scholar]
- 5.Filippou G, Adinolfi A, Iagnocco A, Filippucci E, Cimmino MA. Ultrasound in the diagnosis of calcium pyrophosphate dihydrate deposition disease. A systematic literature review and a meta-analysis. Osteoarthritis Cartilage. 2016;24(6):973–81. 10.1016/j.joca.2016.01.136. Epub 2016 Jan 27. PMID: 26826301. [DOI] [PubMed] [Google Scholar]
- 6.Filippou G, Sirotti S. How can ultrasonography help in the management of CPPD? From diagnosis to clinical subset identification. Curr Opin Rheumatol. 2023;35(3):185–93. 10.1097/BOR.0000000000000939. Epub 2023 Mar 14. PMID: 36943699. [DOI] [PubMed] [Google Scholar]
- 7.Altman R, Asch E, Bloch D, et al. Development of criteria for the classification and reporting of osteoarthritis: classification of osteoarthritis of the knee. Arthritis Rheum. 1986;29(8):1039–49. 10.1002/art.1780290816. [DOI] [PubMed] [Google Scholar]
- 8.Neogi T, Jansen TL, Dalbeth N, et al. 2015 gout classification criteria: an American college of rheumatology/european league against rheumatism collaborative initiative. Ann Rheum Dis. 2015;74(10):1789–98. 10.1136/annrheumdis-2015-208237. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Filippou G, Filippucci E, Tardella M, Bertoldi I, Di Carlo M. etal. Extent and distribution of CPP deposits in patients affected by calcium pyrophosphate dihydrate deposition disease: an ultrasonographic study. Ann Rheum Dis. 2013;72(11):1836-9. 10.1136/annrheumdis-2012-202748. Epub 2013 Mar 26. PMID: 23532170. [DOI] [PubMed]
- 10.Tedeschi SK, Becce F, Pascart T, Guermazi A, Budzik JF. Imaging features of calcium pyrophosphate deposition disease: consensus definitions from an international multidisciplinary working group. Arthritis Care Res (Hoboken). 2023;75(4):825–34. 10.1002/acr.24898. Epub 2022 Nov 23. PMID: 35439343; PMCID: PMC957921. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.MedCalc Software Ltd. Diagnostic test evaluation calculator https://www.medcalc.org/calc/diagnostic_test.php (Version 22.009; accessed September 4, 2023.
- 12.Altman DG, Machin D, Bryant TN, Gardner MJ, editors. Statistics with confidence. 2nd ed. BMJ Books; 2000.
- 13.Mercaldo ND, Lau KF, Zhou XH. Confidence intervals for predictive values with an emphasis to case-control studies. Stat Med. 2007;26:2170–83. [DOI] [PubMed] [Google Scholar]
- 14.Filippou G, Scanu A, Adinolfi A, Toscano C, Gambera D. etal. Criterion validity of ultrasound in the identification of calcium pyrophosphate crystal deposits at the knee: an OMERACT ultrasound study. Ann Rheum Dis. 2021;80(2):261–7. 10.1136/annrheumdis-2020-217998. Epub 2020 Sep 28. PMID: 32988839. [DOI] [PubMed] [Google Scholar]
- 15.Krekeler M, Baraliakos X, Tsiami S, Braun J. High prevalence of chondrocalcinosis and frequent comorbidity with calcium pyrophosphate deposition disease in patients with seronegative rheumatoid arthritis. RMD Open. 2022;8(2):e002383. 10.1136/rmdopen-2022-002383. PMID: 35701012; PMCID: PMC9198698. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Filippou G, Filippucci E, Mandl P, Abhishek A. A critical review of the available evidence on the diagnosis and clinical features of CPPD: do we really need imaging? Clin Rheumatol. 2021;40(7):2581–92. 10.1007/s10067-020-05516-3. Epub 2020 Nov 24. PMID: 33231775. [DOI] [PubMed] [Google Scholar]
- 17.Löffler C, Sattler H, Peters L, Löffler U, Uppenkamp M, Bergner R. Distinguishing gouty arthritis from calcium pyrophosphate disease and other arthritides. J Rheumatol. 2015;42(3):513–20. 10.3899/jrheum.140634. Epub 2014 Nov 15. PMID: 25399385. [DOI] [PubMed] [Google Scholar]
- 18.Filippucci E, Riveros MG, Georgescu D, Salaffi F, Grassi W. Hyaline cartilage involvement in patients with gout and calcium pyrophosphate deposition disease. An ultrasound study. Osteoarthritis Cartilage. 2009;17(2):178–81. 10.1016/j.joca.2008.06.003. Epub 2008 Jul 26. PMID: 18657999. [DOI] [PubMed] [Google Scholar]
- 19.Cipolletta E, Di Matteo A, Smerilli G, Di Carlo M, Di Battista J, Abhishek A, Grassi W, Filippucci E. Ultrasound findings of calcium pyrophosphate deposition disease at metacarpophalangeal joints. Rheumatology (Oxford). 2022;61(10):3997–4005. 10.1093/rheumatology/keac063. PMID: 35104308. [DOI] [PubMed]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
No datasets were generated or analysed during the current study.