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

Prevalence of chondrocalcinosis and calcium pyrophosphate deposition disease in a cohort of adult patients with low alkaline phosphatase levels and a positive versus negative genetic ALPL study

Objectives

To estimate the prevalence of chondrocalcinosis and calcium pyrophosphate dihydrate deposition disease (CPPD) in patients with low alkaline phosphatase (ALP) levels and a positive ALPL genetic study (+GT) for hypophosphatasia (HPP) compared to those with the same biochemical abnormality and a negative genetic test (-GT). As a secondary objective, to analyze the biochemical factors associated with its presence in subjects with ALPL variants.

Methods

Seventy-eight subjects with persistently low ALP levels and ALPL genetic test were included. Baseline and 24-mo knee ultrasounds were performed in 42 + GT and 36 -GT subjects, in whom the fibrocartilage, hyaline cartilage of menisci, tendons, and synovial fluid were scanned to detect calcium pyrophosphate deposits. A MyLabTwice ultrasound machine (Esaote) with a multifrequency linear array transducer (4-13 MHz) was used.

Results

A higher percentage of chondrocalcinosis was observed in the +GT group [9/42 (21.4%)] compared to the -GT group [2/36 (5.6%), p=.045)]. Two patients (4.76%), both in the +GT group, had arthritis secondary to CPPD. No new cases were identified at the 24-mo control. When comparing +GT patients with and without chondrocalcinosis, ALP levels were lower, and pyridoxal-5'-phosphate (PLP) and phosphate levels were higher in the former group (p<.05). Logistic regression analysis revealed that higher PLP levels are associated with the presence of chondrocalcinosis (OR: 1.1; 95% confidence interval, CI, 1.001-1.012).

Conclusions

Chondrocalcinosis was a frequent ultrasonographic finding in HPP. Arthritis secondary to calcium pyrophosphate deposits, however, proved less prevalent. Genetic causes, such as HPP, should be considered when evaluating patients with chondrocalcinosis in clinical practice.

Calcium Pyrophosphate Crystal Formation and Deposition: Where Do we Stand and What Does the Future hold?

PURPOSE OF THE REVIEW

Although calcium pyrophosphate deposition (CPPD) has been known since the 1960s, our understanding of its pathogenesis remains rudimentary. This review aims to illustrate the known mechanisms underlying calcium pyrophosphate (CPP) crystal formation and deposition and explore future directions in research. By examining various perspectives, from basic research to clinical and imaging assessments, as well as new emerging methodologies, we can establish a starting point for a deeper understanding of CPPD pathogenesis.

RECENT FINDINGS

Recent years have seen significant advances in CPPD research, particularly in the clinical field with the development of the 2023 ACR/EULAR classification criteria for CPPD disease, and in imaging with the introduction of the OMERACT ultrasonographic definitions and scoring system. However, progress in basic research has been slower. New laboratory approaches, such as Raman spectroscopy and omics sciences, offer promising insights that may help piece together the puzzle of CPPD. CPPD is a common yet understudied condition. As the population ages and CPPD becomes more prevalent, there is an urgent need to better understand the disease and the mechanisms involved in crystal formation and deposition, in order to improve diagnosis and therapeutic approaches.

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.

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.

An update on the study of synovial fluid in the geriatric patient

BACKGROUND

The characteristics of synovial fluid (SF) in geriatric patients differ from those in younger patients. In Mexico, epidemiologic data on the incidence of different rheumatic diseases in geriatric patients are scarce.

OBJECTIVE

To describe the physical characteristics of geriatric SF and the prevalence of crystals in knee and other joint aspirates from patients with previously diagnosed joint disease.

MATERIALS AND METHODS

A retrospective study was performed with a baseline of 517 SF samples between 2011 and 2023. White blood cell count was performed by Neubauer chamber and crystals were identified by polarized light microscopy. Descriptive statistical analysis was performed and prevalence was reported as a percentage.

RESULTS

The mean age of the adults was 73.5±5.0 years, 54.4% were women and 45.6% were men. The mean SF volume was 6.3±9.5mL in older adults and 15.3±24.9mL in those younger than 65 years. The mean viscosity in older adults was 9.5±4.5mm and the mean leukocyte count was 7352±16,402leukocytes/mm3. Seventy percent of the older adults' SFs were referred to the laboratory for osteoarthritis (OA), with lower proportions for rheumatoid arthritis (RA) (14.6%) and gout (5.1%). Of the crystals observed in the geriatric population, 14.6% corresponded to monosodium urate crystals (CUM) and 18.9% to calcium pyrophosphate crystals (CPP).

CONCLUSIONS

The characteristics of LS in older adults were smaller volume, increased viscosity, and non-inflammatory. The main diagnoses were OA, RA, and gout. The crystal content of the SF of the geriatric population corresponded mainly to CPP.

Selective pyrophosphate detection via metal complexes

Pyrophosphate (PPi) anions are crucial in numerous biological and ecological processes involved in energy conversion, enzymatic reactions, and metabolic regulation along with adenosine. They are also significant biological markers for various processes related to diseases. Fluorescent PPi sensors would enable visual and/or biological detection in convenient settings. However, the current availability of commercial sensors has been limited to costly enzymes that are not compatible for imaging. Sensor development has also encountered challenges such as poor selectivity and stability, and limited practical applications. In this review, we analyze the situation of PPi sensing via commercial kits and focus on sensors that use metal complexes. We address their designs, sensing mechanisms, selectivities and detection limits. Finally, we discuss limitations and perspectives for PPi detection and imaging.

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.