Accuracy of synovial fluid analysis compared to histology for the identification of calcium pyrophosphate crystals: an ancillary study of the OMERACT US Working Group - CPPD subgroup

Diagnosis of calcium pyrophosphate crystal deposition disease by ultrasonography: how many and which sites should be scanned?

OBJECTIVE

To develop the optimal US scanning protocol for the diagnosis of calcium pyrophosphate crystal deposition (CPPD) disease.

METHODS

In this cross-sectional study, consecutive patients with a crystal-proven diagnosis of CPPD disease, and age-, sex-matched disease controls with a negative synovial fluid analysis were prospectively enrolled in two Italian Institutions. Four rheumatologists, blinded to patients' clinical details, performed US examinations using a standardized scanning protocol including 20 joints (shoulders, elbows, wrists, metacarpophalangeal joints from second to fifth fingers, hips, knees, ankles). CPPD was identified as presence/absence, according to the OMERACT definitions. Reduced US scanning protocols were developed by selecting the most informative joints to be imaged by US using the LASSO technique. Patients were randomly divided into training and validation sets. Their diagnostic accuracy was tested comparing the area under the receiver operating characteristic curves.

RESULTS

The number of participants enrolled was 204: 102 with CPPD disease and 102 disease controls [age, mean (s.d.): 71.3 (12.0) vs 71.1 (13.5) years; female: 62.8% vs 57.8%]. The median number of joints with US evidence of CPPD was 5 [interquartile range (IQR): 4-7] and 0 (IQR: 0-1) in patients with CPPD disease and controls, respectively (P < 0.01). The detection of CPPD in ≥2 joints using a reduced scanning protocol (bilateral assessment of knees, wrists and hips) showed a sensitivity of 96.7% (95% CI: 82.8, 99.9) and a specificity of 100 (95% CI: 88.8, 100.0) for the diagnosis of CPPD disease and had good feasibility [mean (s.d.): 12.5 (5.3) min].

CONCLUSION

Bilateral US assessment of knees, wrists and hips had excellent accuracy and good feasibility for the diagnosis of CPPD disease.

Ultrasound reveals a high prevalence of CPPD in consecutive patients with knee pain

The objective of this study is to estimate the prevalence of US findings indicative of calcium pyrophosphate deposition (CPPD) in patients with knee pain. Consecutive patients with knee pain, equally distributed among males and females in seven different age-decades (21-90 years), were enrolled in a cross-sectional study. The presence of US OMERACT-defined CPPD (medial and lateral menisci and femoral hyaline cartilage) and osteophytes (medial and lateral compartments of the tibiofemoral joint) was scored as presence/absence in both knees. Four hundred twenty participants were enrolled (210 men/210 women). Fibrocartilage and hyaline cartilage CPPDs were detected by US in 94/420 (22.4%) and 41/420 (9.8%) participants, respectively. No significant sex differences were noted. The prevalence and the extent of CPPD increased with age. Fibrocartilage and hyaline cartilage CPPDs were identified in 0/60 participants in the third decade, and in 28/60 (46.7%) and 14/60 (23.3%) participants in the ninth decade, respectively (p for trend < 0.01). While fibrocartilage and hyaline cartilage CPPD is virtually absent in subjects younger than 40 and 50 years old, their prevalence steeply increases above from these age groups. Age (aIRR, 1.03; 95% CI, 1.02-1.05), osteophyte score (aIRR, 1.40; 95% CI, 1.22-1.60), and hyaline cartilage CPPD score (aIRR, 2.68; 95% CI, 2.06-3.49) were associated with fibrocartilage CPPD score, whereas age (aIRR, 1.02; 95% CI, 1.01-1.05) and fibrocartilage CPPD score (aIRR, 2.92; 95% CI, 2.29-3.72) were associated with hyaline cartilage CPPD score in multivariable negative binomial regression analyses. In conclusion, we report the US prevalence of CPPD in patients with knee pain. Fibrocartilage CPPD occurs at a younger age and is more prevalent than hyaline cartilage CPPD. Key points • Fibrocartilage CPPD occurs at a younger age and is more prevalent than hyaline cartilage CPPD. • Fibrocartilage and hyaline cartilage CPPDs are virtually absent in subjects younger than 40 and 50 years old. • In subjects older than 80 years, fibrocartilage and hyaline cartilage CPPD prevalence rises up to 46.7% and 23.3%, respectively.

Ultrasound imaging in crystal arthropathies: a pictorial review

OBJECTIVE

The prevalence of crystal arthropathies in the general population is rising. The purpose of this pictorial study is to describe the sonographic elements of the most prevalent crystal arthropathies by emphasizing particular sonographic findings using illustrative images and cases while considering technical details and common pitfalls.

METHODS

Using established recommendations, specialists in the fields of sonography and crystal arthropathies agreed by consensus on the unique ultrasound signs associated with each of the conditions.

RESULTS

Gout, calcium pyrophosphate deposition arthropathy, and hydroxyapatite arthropathy are the three most prevalent crystal arthropathies. Today's high-resolution sonography enables reliable evaluation of the underlying crystal deposits, post-inflammatory changes, and a precise description of joint inflammation.

CONCLUSIONS

High-prevalence crystal arthropathies are reliably detectable by ultrasound with current ultrasound equipment. It is necessary to have extensive ultrasound training, know specific sonographic findings, and understand all possible differential diagnoses for disorders affecting the musculoskeletal system.

How can ultrasonography help in the management of CPPD? From diagnosis to clinical subset identification

PURPOSE OF REVIEW

Clinical manifestations of calcium pyrophosphate deposition (CPPD) disease are quite heterogeneous, ranging from asymptomatic presentation to severe forms of arthritis. In recent years, imaging, particularly ultrasound (US) has gained a central role for the diagnosis of CPPD. However, many questions are still open. Aim of this review is to present how US could be a key tool in the diagnosis and assessment of CPPD and for the identification of subsets of the disease.

RECENT FINDINGS

awareness and research interest around CPPD is increasing in the recent years, as several international taskforces are working on the validation of outcome measures and classification criteria for CPPD, but many pieces of the puzzle are still missing. Recent studies demonstrated that CPPD is an underdiagnosed disease, frequently misdiagnosed as rheumatoid arthritis or polymyalgia rheumatica. US has been increasingly used in the past decade for the diagnosis of CPPD and US definitions have been validated by the OMERACT US working group in the recent years, making of US a valuable tool for diagnosis.

SUMMARY

The most challenging aspects of CPPD are the differential diagnosis with other form of arthritis of the elderly, and the classification of patients in clinical subsets. In this review, we will present the available data for the use of US in the diagnosis of CPPD and we will provide a mainly experienced-based approach to the potential role of the technique in differential diagnosis and phenotypization of patients.

The effect of crystal composition and environment on the color Doppler ultrasound twinkling artifact

Objective.Pathological mineralizations form throughout the body and can be difficult to detect using conventional imaging methods. Color Doppler ultrasound twinkling highlights ∼60% of kidney stones with a rapid color shift and is theorized to arise from crevice microbubbles as twinkling disappears on kidney stones at elevated pressures and scratched acrylic balls in ethanol. Twinkling also sometimes appears on other pathological mineralizations; however, it is unclear whether the etiology of twinkling is the same as for kidney stones.Approach.In this study, five cholesterol, calcium phosphate, and uric acid crystals were grownin vitroand imaged in Doppler mode with a research ultrasound system and L7-4 transducer in water. To evaluate the influence of pressure on twinkling, the same crystals were imaged in a high-pressure chamber. Then, the effect of surface tension on twinkling was evaluated by imaging crystals in different concentrations of surfactant (1%, 2%, 3%, 4%) and ethanol (10%, 30%, 50%, 70%), artificial urine, bovine blood, and a tissue-mimicking phantom.Main results. Results showed that all crystals twinkled in water, with cholesterol twinkling significantly more than calcium phosphate and uric acid. When the ambient pressure was increased, twinkling disappeared for all tested crystals when pressures reached 7 MPa (absolute) and reappeared when returned to ambient pressure (0.1 MPa). Similarly, twinkling across all crystals decreased with surface tension when imaged in the surfactant and ethanol (statistically significant when surface tension <22 mN m^-1) and decreased in blood (surface tension = 52.7 mN m^-1) but was unaffected by artificial urine (similar surface tension to water). In the tissue-mimicking phantom, twinkling increased for cholesterol and calcium phosphate crystals with no change observed in uric acid crystals.Significance.Overall, these results support the theory that bubbles are present on crystals and cause twinkling, which could be leveraged to improve twinkling for the detection of other pathological mineralizations.

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

OBJECTIVE

To assess the reliability and diagnostic accuracy of new radiographic imaging definitions developed by an international multidisciplinary working group for identification of calcium pyrophosphate deposition (CPPD).

METHODS

Patients with knee osteoarthritis scheduled for knee replacement were enrolled. Two radiologists and 2 rheumatologists twice assessed radiographic images for presence or absence of CPPD in menisci, hyaline cartilage, tendons, joint capsule, or synovial membrane, using the new definitions. In case of disagreement, a consensus decision was made and considered for the assessment of diagnostic performance. Histologic examination of postsurgical specimens under compensated polarized light microscopy was the reference standard. Prevalence-adjusted bias-adjusted kappa values were used to assess reliability, and diagnostic performance statistics were calculated.

RESULTS

Sixty-seven patients were enrolled for the reliability study. The interobserver reliability was substantial in most of the assessed structures when considering all 4 readers (κ range 0.59-0.90), substantial to almost perfect among radiologists (κ range 0.70-0.91), and moderate to almost perfect among rheumatologists (κ range 0.46-0.88). The intraobserver reliability was substantial to almost perfect for all the observers (κ range 0.70-1). Fifty-one patients were included in the accuracy study. Radiography demonstrated an overall specificity of 92% for CPPD, but sensitivity remained low for all sites and for the overall diagnosis (54%).

CONCLUSION

The new radiographic definitions of CPPD are highly specific against the gold standard of histologic diagnosis. When the described radiographic findings are present, these definitions allow for a definitive diagnosis of CPPD, rather than other calcium-containing crystal depositions; however, a negative radiographic finding does not exclude the diagnosis.