Detection of calcium pyrophosphate dihydrate crystals in knee meniscus by dual-energy computed tomography

Dual-energy CT in musculoskeletal imaging: technical considerations and clinical applications

Dual-energy CT stands out as a robust and innovative imaging modality, which has shown impressive advancements and increasing applications in musculoskeletal imaging. It allows to obtain detailed images with novel insights that were once the exclusive prerogative of magnetic resonance imaging. Attenuation data obtained by using different energy spectra enable to provide unique information about tissue characterization in addition to the well-established strengths of CT in the evaluation of bony structures. To understand clearly the potential of this imaging modality, radiologists must be aware of the technical complexity of this imaging tool, the different ways to acquire images and the several algorithms that can be applied in daily clinical practice and for research. Concerning musculoskeletal imaging, dual-energy CT has gained more and more space for evaluating crystal arthropathy, bone marrow edema, and soft tissue structures, including tendons and ligaments. This article aims to analyze and discuss the role of dual-energy CT in musculoskeletal imaging, exploring technical aspects, applications and clinical implications and possible perspectives of this technique.

Dual energy computed tomography cannot effectively differentiate between calcium pyrophosphate and basic calcium phosphate diseases in the clinical setting

Background

Recent reports suggested that dual-energy CT (DECT) may help discriminate between different types of calcium phosphate crystals in vivo, which would have important implications for the characterization of crystal deposition occurring in osteoarthritis.

Purpose

Our aim was to test the hypothesis that DECT can effectively differentiate basic calcium phosphate (BCP) from calcium pyrophosphate (CPP) deposition diseases.

Methods

Discarded tissue after total knee replacement specimens in a 71 year-old patient with knee osteoarthritis and chondrocalcinosis was scanned using DECT at standard clinical parameters. Specimens were then examined on light microscopy which revealed CPP deposition in 4 specimens (medial femoral condyle, lateral tibial plateau and both menisci) without BCP deposition. Regions of interest were placed on post-processed CT images using Rho/Z maps (Syngo.via, Siemens Healthineers, VB10B) in different areas of CPP deposition, trabecular bone BCP (T-BCP) and subchondral bone plate BCP (C-BCP).

Results

Dual Energy Index (DEI) of CPP was 0.12 (SD ​= ​0.02) for reader 1 and 0.09 (SD ​= ​0.03) for reader 2, The effective atomic number (Zeff) of CPP was 10.83 (SD ​= ​0.44) for reader 1 and 10.11 (SD ​= ​0.66) for reader 2. Nearly all DECT parameters of CPP were higher than those of T-BCP, lower than those of C-BCP, and largely overlapping with Aggregate-BCP (aggregate of T-BCP and C-BCP).

Conclusion

Differentiation of different types of calcium crystals using DECT is not feasible in a clinical setting.

The patient with a painful knee

Knee pain encompasses a wide array of differential diagnoses and can often pose a diagnostic challenge, as it can have traumatic or non-traumatic causes. A good clinical history, assessment and anatomical knowledge gives a strong foundation to narrow down the diagnosis, and understanding the correct imaging modality and findings further informs correct and timely management. This article reviews various disease processes including fractures, inflammatory, infective and neoplastic causes, and discusses the assessment and various imaging modalities to aid diagnosis in both primary and secondary care.

A reliable and selective ratiometric sensing probe for fluorometric determination of P2O74- based on AIE of GSH@CuNCs-assisted by Al-N@CQDs

In this study, a novel composite material was developed for the ratiometric detection of pyrophosphate anion (P2O74-). This composite consisted of Al and nitrogen co-doped carbon dots (Al-N@CQDs) and glutathione-capped copper nanoclusters (GSH@CuNCs). The Al-N@CQDs component, with its high reserved coordination capacity of Al3+, induced the non-luminescent behavior of GSH@CuNCs, resulting in an aggregation-induced emission (AIE) effect. The hybrid material (Al-N@CQDs/GSH@CuNCs) exhibited dual-emission signals at 620 nm and 450 nm after integrating the two independent materials utilizing the AIE effect and the fluorescence resonance energy transfer (FRET) approach. This approach represents the first utilization of this composite for ratiometric detection. Nevertheless, upon the addition of P2O74-, the AIE and FRET processes were hindered due to the higher coordination interaction of Al3+ towards P2O74- compared to the amino/carboxyl groups on Al-N@CQDs. This successful interference of the AIE and FRET processes allowed for the effective estimation of P2O74-. The response ratio (F450/F620) increased with increasing the concentration of P2O74- in the range of 0.035-160 µM, with an impressive detection limit of 0.012 µM. This innovative approach of utilizing hybrid CQDs/thiolate-capped nanoclusters as a ratiometric fluorescent sensor for analytical applications introduces new possibilities in the field. The as-fabricated system was successfully applied to detect P2O74- in different real samples such as water, serum, and urine samples with acceptable results.

Dual-Energy Computed Tomography and Beyond: Musculoskeletal System

Traditional monoenergetic computed tomography (CT) scans in musculoskeletal imaging provide excellent detail of bones but are limited in the evaluation of soft tissues. Dual-energy CT (DECT) overcomes many of the traditional limitations of CT and offers anatomical details previously seen only on MR imaging. In addition, DECT has benefits in the evaluation and characterization of arthropathies, bone marrow edema, and collagen applications in the evaluation of tendons, ligaments, and vertebral discs. There is current ongoing research in the application of DECT in arthrography and bone mineral density calculation.

ACR Appropriateness Criteria® Chronic Extremity Joint Pain-Suspected Inflammatory Arthritis, Crystalline Arthritis, or Erosive Osteoarthritis: 2022 Update

Evaluation for suspected inflammatory arthritis as a cause for chronic extremity joint pain often relies on imaging. It is essential that imaging results are interpreted in the context of clinical and serologic results to add specificity because there is significant overlap of imaging findings among the various types of arthritis. This document provides recommendations for imaging evaluation of specific types of inflammatory arthritis, including rheumatoid arthritis, seronegative spondyloarthropathy, gout, calcium pyrophosphate dihydrate disease (or pseudogout), and erosive osteoarthritis. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances in which peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Imaging Features of Calcium Pyrophosphate Deposition Disease: Consensus Definitions From an International Multidisciplinary Working Group

OBJECTIVE

To develop definitions for imaging features being considered as potential classification criteria for calcium pyrophosphate deposition (CPPD) disease, additional to clinical and laboratory criteria, and to compile example images of CPPD on different imaging modalities.

METHODS

The American College of Rheumatology and European Alliance of Associations for Rheumatology CPPD classification criteria Imaging Advisory Group (IAG) and Steering Committee drafted definitions of imaging features that are characteristic of CPPD on conventional radiography (CR), conventional computed tomography (CT), dual-energy CT (DECT), and magnetic resonance imaging (MRI). An anonymous expert survey was undertaken by a 35-member Combined Expert Committee, including all IAG members. The IAG and 5 external musculoskeletal radiologists with expertise in CPPD convened virtually to further refine item definitions and voted on example images illustrating CR, CT, and DECT item definitions, with ≥90% agreement required to deem them acceptable.

RESULTS

The Combined Expert Committee survey indicated consensus on all CR definitions. The IAG and external radiologists reached consensus on CT and DECT item definitions, which specify that calcium pyrophosphate deposits appear less dense than cortical bone. The group developed an MRI definition and acknowledged limitations of this modality for CPPD. Ten example images for CPPD were voted acceptable (4 CR, 4 CT, and 2 DECT), and 3 images of basic calcium phosphate deposition were voted acceptable to serve as contrast against imaging features of CPPD.

CONCLUSION

An international group of rheumatologists and musculoskeletal radiologists defined imaging features characteristic of CPPD on CR, CT, and DECT and assembled a set of example images as a reference for future clinical research studies.

Protein-directed synthesis of fluorescent sulfur quantum dots for highly robust detection of pyrophosphate

Inorganic pyrophosphate anions (PPi) play a key role in various biological processes and act as an essential indicator for physiological function evaluation and disease diagnosis. However, there is still a lack of available approaches for straightforward, robust, and convenient PPi detection. Herein, we design an on-off-on fluorescent switching nanoprobe employing Fe³⁺-mediated fluorescent sulfur quantum dots (SQDs) for highly robust detection of PPi. The bovine serum protein (BSA)-capped SQDs with fine water dispersibility and good optical stability are synthesized by an H₂O₂-assisted chemical etching reaction. Specifically, Fe³⁺ can strongly induce the aggregation of the SQDs into relatively larger sizes, resulting in aggregation-induced fluorescence quenching behavior. PPi can selectively bind with Fe³⁺ via emulative coordination and in preventing the aggregation of SQDs this is accompanied by recovery of fluorescence. The physicochemical properties of aggregated and disaggregated SQDs have been systematically investigated. Aggregation and disaggregation of the SQDs and the corresponding quenching and recovery of fluorescence occurs and guarantees the high-contrast sensing performance of the SQD system in complex and challenging aquatic environments. Our designed on-off-on nanoswitch holds great potential for the design of elemental quantum dot-based biosensors for the highly robust detection of analytes in the near future.

Identifying Potential Classification Criteria for Calcium Pyrophosphate Deposition Disease: Item Generation and Item Reduction

OBJECTIVE

Classification criteria for calcium pyrophosphate deposition (CPPD) disease will facilitate clinical research on this common crystalline arthritis. Our objective was to report on the first 2 phases of a 4-phase process for developing CPPD classification criteria.

METHODS

CPPD classification criteria development is overseen by a 12-member steering committee. Item generation (phase I) included a scoping literature review of 5 literature databases and contributions from a 35-member combined expert committee and 2 patient research partners. Item reduction and refinement (phase II) involved a combined expert committee meeting, discussions among clinical, imaging, and laboratory advisory groups, and an item-rating exercise to assess the influence of individual items toward classification. The steering committee reviewed the modal rating score for each item (range -3 [strongly pushes away from CPPD] to +3 [strongly pushes toward CPPD]) to determine items to retain for future phases of criteria development.

RESULTS

Item generation yielded 420 items (312 from the literature, 108 from experts/patients). The advisory groups eliminated items that they agreed were unlikely to distinguish between CPPD and other forms of arthritis, yielding 127 items for the item-rating exercise. Fifty-six items, most of which had a modal rating of +/- 2 or 3, were retained for future phases. As numerous imaging items were rated +3, the steering committee recommended focusing on imaging of the knee and wrist and 1 additional affected joint for calcification suggestive of CPP crystal deposition.

CONCLUSION

A data- and expert-driven process is underway to develop CPPD classification criteria. Candidate items comprise clinical, imaging, and laboratory features.

Periarticular calcifications

Periarticular calcification and ossification is a frequent finding on imaging and may sometimes pose a diagnostic challenge. The differential diagnoses for this radiological finding are wide and can be classified into broad groups such as idiopathic, developmental, trauma, burns, infection, tumor, connective tissue disease, crystalline, metabolic, vascular, and foreign bodies. With careful consideration of the clinical and imaging findings as well as awareness of mimickers of periarticular mineralization, the list of differential diagnoses can be narrowed down. This article aims to review the clinical-radiologic findings of periarticular calcified or ossified lesions with relevant imaging illustrations.

Chondrocalcinosis does not affect functional outcome and prosthesis survival in patients after total or unicompartmental knee arthroplasty: a systematic review

PURPOSE

There are contentious data about the role calcium pyrophosphate (CPP) crystals and chondrocalcinosis (CC) play in the progression of osteoarthritis (OA), as well as in the outcomes after knee arthroplasty. Hence, the purpose of this systematic review was to analyse the clinical and functional outcome, progression of OA and prosthesis survivorship after unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) in patients with CC compared to patients without CC.

METHODS

A systematic review of the literature in PubMed, Medline, Embase and Web of Science was performed using the "Preferred Reporting Items for Systematic Reviews and Meta-Analysis" (PRISMA) guidelines. Articles which reported the outcome and survival rates of prosthesis after TKA or UKA in patients with CC were included.

RESULTS

A total of 3718 patient knees were included in eight selected publications, with a median sample sizes of 234 knees (range 78-1000) and 954 knees (range 408-1500) for publications including UKA and TKA, respectively. At time of surgery, the mean age was 69 years and the prevalence for CC ranged from 12.6 to 36%. Chondrocalcinosis did not significantly influence the functional and clinical outcome, the implant survival as well as the radiologic progression of OA disease after UKA and TKA.

CONCLUSION

The presence of CPP crystals in tissue samples, synovial fluid or evidence of calcifications on preoperative radiographs did not significantly influence the postoperative functional and activity scores. It also had no significant influence on prosthesis survival rate, whether it was a UKA or a TKA. This study shows that the impact of a subclinical form of chondrocalcinosis may not be of clinical relevance in the context of arthroplasty.

LEVEL OF EVIDENCE

IV.

Review: Outcome measures in calcium pyrophosphate deposition

This review highlights outcomes for patients with calcium pyrophosphate deposition (CPPD) reported in prior studies and underscores challenges to assessing outcomes of this condition. Prior clinical studies of interventions for CPPD focused on joint damage and calcification on imaging tests, joint pain, swelling, and inflammatory biomarkers. Qualitative interviews with patients with CPPD and healthcare providers additionally identified flares, overall function, and use of analgesic medications as important outcomes. Imaging evidence of joint damage and calcification is likely to be outcomes in future clinical studies of CPPD, though reliability and sensitivity to change in CPPD require further testing for several imaging modalities. Challenges to outcome measurement in CPPD include questions of attribution of signs and symptoms to CPPD versus co-existing forms of arthritis, lack of therapies to prevent or dissolve calcium pyrophosphate crystal deposition, absence of validated patient- or physician-reported CPPD outcome measures, and scarcity of large cohorts in which to study outcomes of different clinical presentations of CPPD.

The role of dual energy computed tomography in the differentiation of acute gout flares and acute calcium pyrophosphate crystal arthritis

Objectives

To analyse the diagnostic impact of dual energy computed tomography (DECT) in acute gout flares and acute calcium pyrophosphate (CPP) crystal arthritis when compared to the gold standard of arthrocentesis with compensated polarised light microscopy. Microscopy results were also compared to musculoskeletal ultrasound (MUS), conventional radiographs, and the suspected clinical diagnosis (SCD).

Methods

Thirty-six patients with a suspected gout flare (n = 24) or acute CPP crystal arthritis (n = 11, n = 1 suffered from neither) who received a DECT and underwent arthrocentesis were included. Two independent readers assessed DECT images for signs of monosodium urate crystals or calcium pyrophosphate deposition.

Results

Sensitivity of DECT for gout was 63% (95% CI 0.41–0.81) with a specificity of 92% (0.41–0.81) while sensitivity and specificity for acute CPP arthritis were 55% (0.23–0.83) and 92% (0.74–0.99), respectively. MUS had the highest sensitivity of all imaging modalities with 92% (0.73–0.99) and a specificity of 83% (0.52–0.98) for gout, while sensitivity and specificity for acute CPP crystal arthritis were 91% (0.59–1.00) and 92% (0.74–0.99), respectively.

Conclusion

DECT is an adequate non-invasive diagnostic tool for acute gout flares but might have a lower sensitivity than described by previous studies. Both MUS and SCD had higher sensitivities than DECT for acute gout flares and acute CPP crystal arthritis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10067-021-05949-4.

Dual-Energy Computed Tomography for Detection and Characterization of Monosodium Urate, Calcium Pyrophosphate, and Hydroxyapatite: A Phantom Study on Diagnostic Performance

OBJECTIVES

The aim of this study was to determine the diagnostic performance of dual-energy computed tomography (DECT) to detect and distinguish crystal deposits in a phantom. The primary objective was to determine the cutoff DECT ratio and the cross-sectional area (CSA) of a crystal deposit necessary to differentiate monosodium urate (MSU), calcium pyrophosphate (CPP), and calcium hydroxyapatite (HA) using DECT. Our secondary objective was to determine the concentration for limit of detection for MSU, CPP, and HA crystal deposits. Exploratory objectives included the comparison between 2 generations of DECT scanners from the same manufacturer as well as different scanner settings.

MATERIALS AND METHODS

We used a cylindrical soft tissue phantom with synthetic MSU, CPP, and HA crystals suspended in resin. Crystal suspension concentration increased with similar attenuation between MSU, CPP, and HA in conventional CT. The phantom was scanned on 2 dual-source DECT scanners, at 2 dose levels and all available tube voltage combinations. Both scanners had a tin (Sn) filter at the high-energy spectra. Dual-energy CT ratios were calculated for a given tube voltage combination by dividing linear regression lines of CT numbers against concentration. Dual-energy CT ratios were compared using an analysis of covariance. Receiver operating characteristic curves and corresponding areas under the curve (AUCs) were calculated for individual crystal suspension comparisons (HA vs CPP, MSU vs CPP, and MSU vs HA).

RESULTS

At standard clinical scan settings with 8 mGy and 80/Sn150 kV, the DECT ratios were as follows: CPP, 2.02 (95% confidence interval [CI], 1.98-2.07); HA, 2.00 (95% CI, 1.96-2.05); and MSU, 1.09 (95% CI, 1.06-1.11). Ratios varied numerically depending on the scanner and tube voltage combination. Monosodium urate crystal DECT ratios were significantly different from HA and CPP (P < 0.001), whereas DECT ratios for HA and CPP crystals did not differ significantly (P = 0.99). The differentiation of MSU crystals from both calcium crystals (HA and CPP) was excellent with an AUC of 1.00 (95% CI, 1.00-1.00) and an optimal cutoff DECT ratio of 1.43:1.40 depending on the scanner. In addition, differentiation of MSU and calcium-containing crystals (HA and CPP) required a CSA of minimum 4 pixels of crystal at standard clinical scan conditions. In contrast, differentiation between CPP and HA crystals was moderate with AUCs ranging from 0.66 (95% CI, 0.52-0.80) to 0.80 (95% CI, 0.69-0.91) and an optimal cutoff DECT ratio of 2.02:2.06 depending on the scanner. Furthermore, differentiation between CPP and HA crystals required a CSA of minimum 87 pixels of crystal at standard clinical scan conditions, corresponding to a region of interest of 3.7 mm diameter. When scanning at highest possible spectral separation and maximum dose of 50 mGy, the limit of detection for crystals within a region of interest of 50 pixels was 14 mg/cm3 for MSU and 2 mg/cm3 for both CPP and HA.

CONCLUSIONS

This phantom study shows that DECT can be used to detect MSU, CPP, and HA crystal deposits. Differentiation of CPP and HA was not possible in crystals deposits less than 3.7 mm in diameter, but MSU could accurately be differentiated from CPP and HA crystal deposits at standard clinical scan conditions.

The role of Interleukin-1 receptor antagonist as a treatment option in calcium pyrophosphate crystal deposition disease

Calcium Pyrophosphate Crystal Deposition (CPPD) disease is characterized by the deposition of calcium pyrophosphate crystals in the cartilage. In most cases, it can manifest as a subclinical condition named chondrocalcinosis, often revealed by joint x-ray examination. In other cases, deposition can cause flares of arthritis, known as acute CPP crystal arthritis. In the last few years, many pathogenic pathways have been discovered. Interleukin-1 (IL-1) plays a key role in the pathogenesis of CPPD disease, both as a mediator of inflammatory response to crystals and as a promoter of damage to articular cartilage. In this review, we investigated the role of IL-1R inhibitor, such as Anakinra, as an alternative to the various therapeutic strategies for CPPD disease, especially among patients resistant to traditional treatment with NSAIDs, corticosteroids and colchicine.

The diagnostic value of conventional radiography and musculoskeletal ultrasonography in calcium pyrophosphate deposition disease: a systematic literature review and meta-analysis

OBJECTIVE

To examine and compare the accuracy of conventional radiography (CR) and musculoskeletal ultrasonography (US) in the diagnosis of calcium pyrophosphate (CPP) crystals deposition disease (CPPD).

DESIGN

A systematic search of electronic databases (PubMed, Embase, and Cochrane), conference abstracts and reference lists was undertaken. Studies which evaluated the accuracy of CR and/or US in the diagnosis of CPPD, using synovial fluid analysis (SFA), histology or classification criteria as reference tests were included. Subgroup analyses by anatomic site and by reference test were performed.

RESULTS

Twenty-six studies were included. Using SFA/histology as reference test, CR and US showed an excellent (CR AUC = 0.889, 95%CI = 0.811-0.967) and an outstanding (US AUC = 0.954, 95%CI = 0.907-1.0) diagnostic accuracy (p < 0.01), respectively. Furthermore, US showed a higher sensitivity (0.85, 95%CI = 0.79-0.90 vs 0.47, 95%CI = 0.40-0.55) and only a little lower specificity (0.87, 95%CI = 0.83-0.91 vs 0.95, 95%CI = 0.92-0.97) than CR. A considerable heterogeneity between the studies was found, with adopted reference test being the main source of heterogeneity. In fact, subgroup analysis showed a significant change in the diagnostic accuracy of CR, but not of US, using Ryan and McCarty criteria or SFA/histology as reference test (CR: AUC = 0.956, 95%CI = 0.925-1.0 vs AUC = 0.889, 95%CI = 0.828-0.950, respectively, p < 0.01) (US: AUC = 0.922, 95%CI = 0.842-1.0 vs AUC = 0.957, 95%CI = 0.865-1.0, respectively, p = 0.08) CONCLUSIONS: Although US is more sensitive and a little less specific than CR for identifying CPP crystals, both these two techniques showed a great diagnostic accuracy and should be regarded as complementary to each other in the diagnostic work-up of patients with CPPD.

Apoptosis in the Extraosseous Calcification Process

Extraosseous calcification is a pathologic mineralization process occurring in soft connective tissues (e.g., skin, vessels, tendons, and cartilage). It can take place on a genetic basis or as a consequence of acquired chronic diseases. In this last case, the etiology is multifactorial, including both extra- and intracellular mechanisms, such as the formation of membrane vesicles (e.g., matrix vesicles and apoptotic bodies), mitochondrial alterations, and oxidative stress. This review is an overview of extraosseous calcification mechanisms focusing on the relationships between apoptosis and mineralization in cartilage and vascular tissues, as these are the two tissues mostly affected by a number of age-related diseases having a progressively increased impact in Western Countries.

Calcium pyrophosphate crystal size and characteristics

Objective:

To describe the characteristics of calcium pyrophosphate (CPP) crystal size and morphology under compensated polarized light microscopy (CPLM). Secondarily, to describe CPP crystals seen only with digital enhancement of CPLM images, confirmed with advanced imaging techniques.

Methods:

Clinical lab-identified CPP-positive synovial fluid samples were collected from 16 joint aspirates. Four raters used a standardized protocol to describe crystal shape, birefringence strength and color. A crystal expert confirmed CPLM-visualized crystal identification. For crystal measurement, a high-pass linear light filter was used to enhance resolution and line discrimination of digital images. This process identified additional enhanced crystals not seen by raters under CPLM. Single-shot computational polarized light microscopy (SCPLM) provided further confirmation of the enhanced crystals’ presence.

Results:

Of 932 suspected crystals identified by CPLM, 569 met our inclusion criteria, and 293 (51%) were confirmed as CPP crystals. Of 175 unique confirmed crystals, 118 (67%) were rods (median area 3.6 μm² [range, 1.0–22.9 μm²]), and 57 (33%) were rhomboids (median area 4.8 μm² [range, 0.9–16.7 μm²]). Crystals visualized only after digital image enhancement were smaller and less birefringent than CPLM-identified crystals.

Conclusions:

CPP crystals that are smaller and weakly birefringent are more difficult to identify. There is likely a population of smaller, less birefringent CPP crystals that routinely goes undetected by CPLM. Describing the characteristics of poorly visible crystals may be of use for future development of novel crystal identification methods.

Computed tomography in rheumatology - From DECT to high-resolution peripheral quantitative CT

In this chapter, we discuss current updates and applications of Dual Energy Computed Tomography (DECT), iodine-DECT mapping, and high-resolution peripheral quantitative CT (HR-pQCT) in rheumatology. DECT provides a noninvasive diagnosis of gout and can help to differentiate gout from CPPD. Accuracy of DECT varies in various stages of gout. DECT needs specialized hardware, software, and skilled post-processing and interpretation. Sensitivity reduces significantly with deeper tissues such as hip and shoulder. Iodine map enables to delineate inflammatory lesions such as capsulitis and tenosynovitis by improving iodine contrast. Iodine quantification with an iodine map is a promising objective method to evaluate therapeutic effect of inflammatory arthritis. HR-pQCT allows for highly sensitive and specific measures of bone erosions and osteophytes in inflammatory joint diseases, documenting change over time, e.g. in cohorts undergoing immunosuppressive treatments. However, assessing the images requires trained readers, and (semi)-automated scripts to detect bone damage are still undergoing validation and further development.

A critical review of the available evidence on the diagnosis and clinical features of CPPD: do we really need imaging?

Imaging has been playing an important role in the pathogenetic and clinical characterisation of many rheumatic diseases, especially in the most recent years with the advent of many new, highly technological and promising techniques. Calcium pyrophosphate deposition disease (CPPD) benefited also from these new techniques, most of which can readily identify calcium crystals. Nowadays, imaging is used mainly to identify crystals in joints but given the complexity of CPPD, imaging should be used with an "holistic" approach in order to gain insights in the pathogenesis, spectrum of clinical manifestations and natural history of the disease. Furthermore, overlap or association of CPPD with other prevalent diseases of the elderly makes the differential diagnosis challenging. In this review, we provide a critical review of the current knowledge on the use of imaging both for the identification of crystals and for its application in clinical practice as an aid for determining the impact of the disease on patients.Key Points• CPPD is a complex disease with a wide spectrum of clinical manifestations and understanding of pathogenetic mechanisms and clinical phenotypes is essential for correct characterisation• Imaging has made important advances regarding identification of CPPD in recent years, and new, more sophisticated techniques are under investigation• Imaging has the potential to improve our knowledge on pathogenesis and clinical phenotypes of CPPD• Imaging techniques have to be tested thoroughly for reliability, discrimination and sensitivity to change before they can be implemented in clinical trials.

Can Dual-Energy Computed Tomography Be Used to Identify Early Calcium Crystal Deposition in the Knees of Patients With Calcium Pyrophosphate Deposition?

OBJECTIVE

To assess the ability of dual-energy computed tomography (DECT) in identifying early calcium crystal deposition in menisci and articular cartilage of the knee, depending on the presence/absence of chondrocalcinosis seen on conventional CT.

METHODS

One hundred thirty-two knee DECT scans from patients with suspected crystal-associated arthropathy were reviewed and assigned to a calcium pyrophosphate deposition (CPPD) group (n = 50) or a control group (n = 82). Five DECT attenuation parameters were measured in preset regions of interest (ROIs) in menisci and articular cartilage and compared between groups using linear mixed models with adjustment for confounders. Subgroup analysis, excluding ROIs with chondrocalcinosis seen on conventional CT, was performed.

RESULTS

In both menisci and articular cartilage, and for all 5 DECT attenuation parameters, calcified ROIs in CPPD patients showed significantly higher values than ROIs in controls (P ≤ 0.036). Conversely, noncalcified ROIs in CPPD patients were comparable with those in controls (P ≥ 0.09). While specific DECT parameters yielded good accuracy (area under the curve [AUC] 0.87-0.88) in differentiating calcified ROIs in CPPD patients from ROIs in controls, DECT failed to distinguish between noncalcified ROIs in CPPD patients and controls (AUC 0.58-0.59).

CONCLUSION

While DECT has the potential to characterize knee intraarticular mineralization, this technique cannot yet accurately identify early calcium crystal deposition that is not visible as chondrocalcinosis on conventional CT.

Imaging of crystalline arthropathy in 2020

Crystal-related arthropathies are the result of crystal deposition in joint and periarticular soft tissues. Identification of urate crystals is mandatory to distinguish gout from other crystalline arthropathies, including calcium pyrophosphate dihydrate and basic calcium phosphate crystal deposition diseases. ACR/EULAR classification criteria for gout included dual-energy computed tomography and ultrasound with equal impact to the final score. Different diagnostic strengths of these imaging modalities depend on disease duration and scanned anatomic site. While ultrasound has been indicated as the first-choice imaging technique, especially in the early stages of the disease, dual-energy computed tomography has shown to be highly specific, allowing the detection of crystal deposits in anatomic sites not accessible by ultrasound, such as the spine. At the spinal level, MRI findings are usually nonspecific. Finally, there is preliminary evidence that at the knee, dual-energy computed tomography may discriminate calcium pyrophosphate dihydrate from basic calcium phosphate crystal deposits.

Calcium pyrophosphate deposition disease: The role of imaging in their detection and in differential diagnosis of crystal arthropathies

Calcium pyrophosphate deposition disease is characterized by the deposition of pyrophosphate crystals in various joint structures. Calcium pyrophosphate deposition disease can be linked to underlying metabolic disorders such as hemochromatosis, hyperparathyroidism, hypophosphatemia, hypomagnesaemia, and hypothyroidism, all of which increase the risk of calcium pyrophosphate deposition. We present the case of a 55-year-old male who underwent diagnostic examination for the onset of recurrent joint pain in the right knee.

Utility of Ultrasound and Dual Energy CT in Crystal Disease Diagnosis and Management

PURPOSE OF REVIEW

The objective of this review is to critically discuss the latest evidence on the use of ultrasound and dual energy computed tomography (DECT) for the assessment of microcrystalline arthritis.

RECENT FINDINGS

Both techniques have been included in the classification and diagnostic criteria for gout, while only ultrasound appears in the diagnostic recommendations for CPPD. Regarding the management of the diseases, there is encouraging evidence for the use of both techniques for the follow-up of gout patients, while very few or null data are available for CPPD. Ultrasound has been adequately validated for the diagnosis of CPPD, while some issues have still to be clarified regarding gout. DECT has also demonstrated to be accurate for gout diagnosis, but very few data are available regarding CPPD. Future research should aim to improve the reliability of both techniques and to create scoring systems for a more accurate follow-up of patients.

Dual-energy computed tomography in calcium pyrophosphate deposition: initial clinical experience

OBJECTIVE

To determine the dual-energy computed tomography (DECT) attenuation properties of meniscal calcifications in calcium pyrophosphate deposition (CPPD) in vivo, and assess whether DECT was able to discriminate meniscal CPP deposits from calcium hydroxyapatite (HA) in subchondral and trabecular bone.

METHOD

Patients with clinical suspicion of crystal-related arthropathy (gout and/or CPPD) and knee DECT scans were retrospectively assigned to CPPD (n = 19) or control (n = 21) groups depending on the presence/absence of chondrocalcinosis on DECT. Two observers drew standardized regions of interest (ROI) in meniscal calcifications, non-calcified menisci, as well as subchondral and trabecular bone. Five DECT parameters were obtained: CT numbers (HU) at 80 and 140 kV, dual-energy index (DEI), electron density (ρ_e), and effective atomic number (Z_eff). The four different knee structures were compared within/between patients and controls using linear mixed models, adjusting for confounders.

RESULTS

Meniscal calcifications (n = 89) in CPPD patients had mean ± SD CT numbers at 80 and 140 kV of 257 ± 64 and 201 ± 48 HU, respectively; with a DEI of 0.023 ± 0.007, and ρ_e and Z_eff of 140 ± 35 and 8.8 ± 0.3, respectively. Meniscal CPP deposits were readily distinguished from calcium HA in subchondral and trabecular bone (p ≤ 0.001), except at 80 kV separately (p = 0.74). Z_eff and ρ_e both significantly differed between CPP deposits and calcium HA in subchondral and trabecular bone (p < 0.0001).

CONCLUSION

This proof-of-concept study shows that DECT has the potential to discriminate meniscal CPP deposits from calcium HA in subchondral and trabecular bone in vivo, paving the way for the non-invasive biochemical signature assessment of intra- and juxta-articular calcium crystal deposits.

Issues in CPPD Nomenclature and Classification

PURPOSE OF REVIEW

This paper covers confusion and challenges in the nomenclature of calcium pyrophosphate deposition disease. Clinicians, investigators, and patients are faced with a variety of terms that are used to describe CPPD and its phenotypes, and clarity is greatly needed to help advance research and patient care. Motivation for the upcoming development of CPPD classification criteria is reviewed.

RECENT FINDINGS

EULAR proposed recommended terminology for CPPD in 2011. International Classification of Diseases (ICD-9 and ICD-10) billing codes identify definite or probable CPPD with variable accuracy depending on the clinical setting and comparator group. READ diagnostic codes have been employed to identify pseudogout in UK datasets but their accuracy has not been evaluated. CPPD classification criteria will provide a system for identifying a relatively homogenous group of patients to be included in clinical studies, enabling comparison of outcomes across studies. CPPD nomenclature remains challenging for clinicians, investigators, and patients. A lay-friendly definition of CPPD, using easily accessible terminology, would be welcome. CPPD classification criteria are a necessary step in moving forward CPPD clinical research and may involve a range of clinical, laboratory, and imaging modalities.

Diagnostic value of ultrasound in calcium pyrophosphate deposition disease of the knee joint

OBJECTIVE

To assess the diagnostic performance of ultrasound (US) for calcium pyrophosphate deposition (CPPD) at the level of menisci, hyaline cartilage (HC), tendons, and synovial fluid (SF) of the knee, and to examine inter- and intra-observer reliability.

DESIGN

We consecutively included patients with knee effusion over a 2-year period (43 patients with CPPD and 131 controls). All patients underwent SF analysis, conventional radiography (CR), and US examination using the Outcome Measures in Rheumatology (OMERACT) definition of the US characteristics of CPPD. Two independent operators performed the US, and inter-observer agreement was calculated. Intra-observer agreement was examined with static images obtained for all enrolled patients.

RESULTS

US revealed calcium pyrophosphate (CPP) deposits in menisci, HC, and tendon more frequently in patients with CPPD than in control patients. The presence of US CPP deposits in SF was not significantly different between the two groups. Combined US evaluation of the three components (menisci, HC, and tendon) showed the best diagnostic performance. The sensitivity and specificity for US evaluation of the three components were 74.4% and 77.1%, respectively, while for CR evaluation, the sensitivity and specificity were 44.2% and 96.9%, respectively. Inter- and intra-observer agreement were excellent for medial (κ = 0.930, 0.972) and lateral menisci (κ = 0.905, 0.942), HC (κ = 0.844, 0.957), and SF (κ = 0.817, 0.925). Tendon showed fair inter-observer (κ = 0.532) and good intra-observer reliability (κ = 0.788).

CONCLUSIONS

Based on the OMERACT definition, US demonstrated better diagnostic capacity than CR to diagnose CPPD, with excellent reliability. Combined evaluation of menisci, HC, and tendon showed the best diagnostic accuracy.

Diagnostic advances in synovial fluid analysis and radiographic identification for crystalline arthritis

PURPOSE OF REVIEW

The present review addresses diagnostic methods for crystalline arthritis including synovial fluid analysis, ultrasound, and dual energy CT scan (DECT).

RECENT FINDINGS

There are new technologies on the horizon to improve the ease, sensitivity, and specificity of synovial fluid analysis. Raman spectroscopy uses the spectral signature that results from a material's unique energy absorption and scatter for crystal identification. Lens-free microscopy directly images synovial fluid aspirate on to a complementary metal-oxide semiconductor chip, providing a high-resolution, wide field of view (∼20 mm) image. Raman spectroscopy and lens-free microscopy may provide additional benefit over compensated polarized light microscopy synovial fluid analysis by quantifying crystal density in synovial fluid samples. Ultrasound and DECT have good sensitivity and specificity for the identification of monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals. However, both have limitations in patients with recent onset gout and low urate burdens.

SUMMARY

New technologies promise improved methods for detection of MSU and CPP crystals. At this time, limitations of these technologies do not replace the need for synovial fluid aspiration for confirmation of crystal detection. None of these technologies address the often concomitant indication to rule out infectious arthritis.