Crystal identification of synovial fluid aspiration by polarized light microscopy. An online test suggesting that our traditional rheumatologic competence needs renewed attention and training

Discovery of calcite as a new pro-inflammatory calcium-containing crystal in human osteoarthritic synovial fluid

OBJECTIVE

We aimed to characterize calcium-containing crystals present in synovial fluid from patients with knee osteoarthritis (OA) using Raman spectroscopy, and specifically investigate the biological effects of calcite crystals.

DESIGN

Thirty-two synovial fluid samples were collected pre-operatively from knee OA patients undergoing total joint arthroplasty. An integrated Raman polarized light microscope was used for identification of crystals in synovial fluid. Human peripheral blood mononuclear cells (PBMC's), human OA articular chondrocytes (HACs) and fibroblast-like synoviocytes (FLSs) were exposed to calcite crystals. Expression of relevant cytokines and inflammatory genes were measured using ELISA and real-time PCR.

RESULTS

Various calcium-containing crystals were identified, including calcium pyrophosphate (37.5 %) and basic calcium phosphate (21.8 %), but they were never found simultaneously in the same OA synovial fluid sample. For the first time, we discovered the presence of calcite crystals in 93.8 % of the samples, while dolomite was detected in 25 % of the cases. Characterization of the cellular response to calcite crystal exposure revealed increased production of innate immune-derived cytokines by PBMC's, when co-stimulated with lipopolysaccharide (LPS). Additionally, calcite crystal stimulation of HACs and FLSs resulted in enhanced secretion of pro-inflammatory molecules and alterations in the expression of extracellular matrix remodeling enzymes.

CONCLUSIONS

This study highlights the unique role of Raman spectroscopy in OA crystal research and identified calcite as a novel pro-inflammatory crystal type in OA synovial fluid. Understanding the role of specific crystal species in the OA joint may open new avenues for pharmacological interventions and personalized approaches to treating OA.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Diagnostic Accuracy of Raman Spectroscopy Integrated With Polarized Light Microscopy for Calcium Pyrophosphate-Associated Arthritis

OBJECTIVE

We studied the performance of integrated Raman polarized light microscopy (iRPolM) for the identification of calcium pyrophosphate (CPP)-associated arthritis (CPPD).

METHODS

This is a diagnostic accuracy study including 400 consecutive synovial fluid samples from a single hospital in the Netherlands. Accuracy measures were calculated against polarized light microscopy (PLM) and the 2023 American College of Rheumatology (ACR)/EULAR criteria set for CPPD.

RESULTS

The interrater reliability between iRPolM and the 2023 ACR/EULAR criteria set for CPPD was strong (κ = 0.88). The diagnostic performance of iRPolM compared to the 2023 ACR/EULAR criteria set was sensitivity 86.0% (95% confidence interval [CI] 73.3-94.2), specificity 99.1% (95% CI 97.5-99.8), positive likelihood ratio 100.33 (95% CI 32.3-311.3), negative likelihood ratio 0.14 (95% CI 0.07-0.28), positive predictive value 93.5% (95% CI 82.2-97.8), negative predictive value 98.0% (95% CI 82.2-97.8), and accuracy 97.5% (95% CI 95.5-98.8). We allowed rheumatologists to rate the certainty of their microscopic identification of CPP and found a large correspondence between iRPolM and a certain identification (κ = 0.87), whereas only 10% of the uncertain CPP identifications could be confirmed with iRPolM. We identified several novel particle types in synovial fluid analysis, including calcium carbonate crystals, deposited carotenoids, microplastics, and three types of Maltese cross birefringent objects.

CONCLUSION

iRPolM can easily identify CPP crystals with a strong diagnostic performance. PLM alone is not specific enough to reliably resolve complicated cases, and the implementation of Raman spectroscopy in rheumatology practice can be of benefit to patients with suspected CPPD.

Test characteristics of Raman spectroscopy integrated with polarized light microscopy for the diagnosis of acute gouty arthritis

OBJECTIVES

We studied the performance of Raman spectroscopy integrated with polarized light microscopy (iRPolM) as a next-generation technique for synovial fluid analysis in gout.

METHODS

This is a prospective study, including consecutive synovial fluid samples drawn from any peripheral swollen joint. Diagnostic accuracy was compared to the 2015 ACR/EULAR Gout classification criteria as a reference test and to polarized light microscopy (PLM) analysis by a rheumatologist. Synovial fluid was analysed with iRPolM after unblinding the PLM results.

RESULTS

Two hundred unselected consecutive patient samples were included in this study. Validation against clinical criteria: 67 patients were classified as gout according to 2015 ACR/EULAR classification criteria. Compared to the 2015 ACR/EULAR gout classification criteria, iRPolM had a sensitivity of 77.6% (95% CI: 65.8-86.9), specificity of 97.7% (95% CI: 93.5-99.5), positive predictive value (PPV) of 94.5% (95% CI: 84.9-98.2), negative predictive value (NPV) of 89.7% (95% CI: 84.7-93.1), an accuracy of 91.0% (95% CI: 86.2-94.6), a positive likelihood ratio of 34.4 (95% CI: 11.16-106.10) and a negative likelihood ratio of 0.23 (95% CI: 0.15-0.36). Validation against PLM: 55 samples were positive for MSU according to PLM. The interrater agreement between PLM and iRPolM was near perfect (к=0.90). The sensitivity of iRPolM to identify MSU in PLM-positive samples was 91.2% (95% CI: 80.7-97.1), the specificity was 97.6% (95% CI: 93.0-99.5), the PPV was 94.6% (95% CI: 85.0-98.2), NPV was 96.0% (95% CI: 91.2-98.2) and the accuracy was 95.6% (95% CI: 91.4-98.2). The positive likelihood ratio was 37.4 (95% CI: 12.20-114.71), and the negative likelihood ratio was 0.09 (95% CI: 0.04-0.21).

CONCLUSION

iRPolM is a promising next-generation diagnostic tool for rheumatology by diagnosing gout with high specificity, increased objectivity, and a sensitivity comparable to PLM.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Diagnosis and Treatment of Calcium Pyrophosphate Deposition (CPPD) Disease: A Review

Calcium Pyrophosphate Dihydrate (CPPD) crystal-related arthropathies are a common cause of acute and chronic arthritis caused by the deposition of calcium pyrophosphate crystals in joints and soft tissues, resulting in inflammation and joint damage. They present with a wide spectrum of clinical manifestations and often present challenges to diagnosis and management as they commonly affect older co-morbid patients. The challenges are compounded by a lack of a well-defined description of CPPD. However, an international expert-driven process is underway to develop CPPD classification criteria. Treatment is also problematic as unlike gout, there are no agents available that decrease the crystal burden. Treatment options have often been extrapolated from gout treatment pathways without having extensive trials or a solid evidence base. It is hoped the new CPPD classification guidelines will contribute to large multicentre studies, with well-defined patient cohorts, which will facilitate the production of high-quality evidence to guide the management of this condition. Here, we discuss the barriers and facilitators in diagnosing and treating CPPD-related arthropathy.

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.

The preservation of synovial fluid using dimethyl sulfoxide

BACKGROUND

The Royal College of Pathologists of Australasia Quality Assurance Programs runs a Quality Assurance Program for the assessment of synovial fluid crystals. It provides aliquots of synovial fluid to various laboratories. The quality of specimens can deteriorate prior to being examined. We aimed to assess whether the addition of dimethyl sulfoxide (DMSO) to synovial fluid specimens helps maintain cellular morphology.

METHODS

Synovial fluid specimens were obtained from 15 patients. Each specimen was aliquoted into 24 samples, with half having DMSO added at a concentration of 10%. For each specimen, six samples containing DMSO and six samples not containing DMSO were stored at-80°C and room temperature. Samples from each group were examined at 1, 2, 3, 6, 7 and 8 weeks. Comparative Analysis: For each specimen, the final remaining aliquoted samples containing DMSO and not containing DMSO, which were stored at-80°C, were directly compared. Quantitative Analysis: A system for grading cellular morphology and assessing for artefacts and cellular clumping was applied by two independent assessors.

RESULTS

Comparative Analysis: A significant difference was found between samples containing DMSO and not containing DMSO which were stored at -80°C (p = .000), in favour of those containing DMSO. Quantitative Analysis: Regarding the combined findings of Assessors 1 and 2 and the grading of cellular morphology, a significant difference was found according to "groups" (p = .000), in favour of those containing DMSO and stored at-80°C.

CONCLUSIONS

DMSO contributes to the maintenance of cellular morphology in synovial fluid when stored in frozen conditions.

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.

One Joint Aspirate: Three Diagnoses

Gout is a frequently diagnosed condition. However, it is rarely diagnosed with concomitant pseudogout or reactive arthritis (ReA) from ​​​​​Chlamydophila pneumoniae (C. pneumoniae). This case report describes an interesting case of a 67-year-old man who presented with a two-week history of malaise, chills, and shortness of breath. He also reported a one-day history of polyarthritis, which limited his ambulation. The results of polarized microscopy revealed uric acid and calcium pyrophosphate crystals. The respiratory panel was positive for C. pneumoniae and rhinovirus. Therefore, he was diagnosed with gout, pseudogout, and ReA. Appropriate management led to a full clinical recovery. This is the first report documenting the simultaneous occurrence of ReA, gout, and pseudogout in a single patient. The association between these rheumatic diseases and a summary of similar cases in the literature are also discussed.

Clinical Validation of Rapid Gout Detection Method and Kit

Gout is an inflammatory arthritis, which causes intense, acute pain due to the buildup of uric acid crystals in synovial fluid. The gold standard for gout diagnosis consists of synovial fluid analysis by polarized light microscopy, which is costly, time-intensive, and technique-dependent, therefore meriting a more efficient, inexpensive, and accessible method for diagnosis. We previously developed and validated a novel colorimetric gout detection method and device based on the reduction of silver nitrate by uric acid; here, we clinically validated our method and device using arthroscopically obtained synovial fluid samples from gout patients. We successfully identified uric acid crystals in clinical samples via our colorimetric method, visualized uric acid crystals in synovial fluid via handheld microscopy, and determined that silver nitrate stain did not interfere with the microscopic visualization of uric acid crystals necessary for diagnosis. We also developed and validated a method of processing turbid clinical samples for use in our device to prevent the obscuration of uric acid crystals by suspended material. Our method and device will clinically facilitate the immediate colorimetric diagnosis of gout and the subsequent bedside visualization of uric acid crystals in both ideal and turbid synovial fluid samples, allowing for a point-of-care diagnosis of gout.

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.

Classifying Pseudogout Using Machine Learning Approaches With Electronic Health Record Data

OBJECTIVE

Identifying pseudogout in large data sets is difficult due to its episodic nature and a lack of billing codes specific to this acute subtype of calcium pyrophosphate (CPP) deposition disease. The objective of this study was to evaluate a novel machine learning approach for classifying pseudogout using electronic health record (EHR) data.

METHODS

We created an EHR data mart of patients with ≥1 relevant billing code or ≥2 natural language processing (NLP) mentions of pseudogout or chondrocalcinosis, 1991-2017. We selected 900 subjects for gold standard chart review for definite pseudogout (synovitis + synovial fluid CPP crystals), probable pseudogout (synovitis + chondrocalcinosis), or not pseudogout. We applied a topic modeling approach to identify definite/probable pseudogout. A combined algorithm included topic modeling plus manually reviewed CPP crystal results. We compared algorithm performance and cohorts identified by billing codes, the presence of CPP crystals, topic modeling, and a combined algorithm.

RESULTS

Among 900 subjects, 123 (13.7%) had pseudogout by chart review (68 definite, 55 probable). Billing codes had a sensitivity of 65% and a positive predictive value (PPV) of 22% for pseudogout. The presence of CPP crystals had a sensitivity of 29% and a PPV of 92%. Without using CPP crystal results, topic modeling had a sensitivity of 29% and a PPV of 79%. The combined algorithm yielded a sensitivity of 42% and a PPV of 81%. The combined algorithm identified 50% more patients than the presence of CPP crystals; the latter captured a portion of definite pseudogout and missed probable pseudogout.

CONCLUSION

For pseudogout, an episodic disease with no specific billing code, combining NLP, machine learning methods, and synovial fluid laboratory results yielded an algorithm that significantly boosted the PPV compared to billing codes.

Synovial fluid analysis for the enhanced clinical diagnosis of crystal arthropathies in a tertiary care institution

INTRODUCTION/OBJECTIVES

Few studies have addressed the detection and clinical impact of different crystals in patients with diverse rheumatologic diagnoses in Latin America. The aim of this study was to assess the consistency between the clinical referring diagnosis and the identification of crystals, such as monosodium urate (MSU) and calcium pyrophosphate (CPP), in the synovial fluid (SF) of patients from a Mexican tertiary care institution.

METHODS

We reviewed the results of 264 SF analyses to identify any changes in diagnosis upon SF analysis. We reported patient medical file data on sex, age, diagnosis, and microscopic SF analysis results. We performed consistency analyses between referring diagnoses and SF findings with McNemar's test.

RESULTS

The prevalence of MSU crystals in SF was noted in 89.1% of gout cases and 9.09% of cases of calcium pyrophosphate disease (CPPD). CPP crystals were present in 54.5% of CPPD cases, 42.9% of osteoarthritis (OA) cases, and 7.27% of gout cases. Calcium hydroxyapatite (HA) crystals were identified in 5.45% of gout cases, 33.3% of rheumatoid arthritis (RA) cases, 57.1% of OA cases, and 63.6% of CPPD cases. Cholesterol and lipid crystals were present in small proportions in RA cases. Glucocorticoid crystals were observed in 1.85% of gout cases, 44.4% of RA cases, and 42.9% of OA cases. We observed an association of MSU identification with clinical suspicion of gout (P = 0.08), CPP with OA (P = 0.26) and CPPD (P = 0.50). An association was noted between HA and the diagnosis of CPPD (P = 0.84) and OA (P > 0.99). The number of initial diagnoses that changed upon SF analysis was 14.3%.

CONCLUSIONS

SF analysis has major diagnostic value regarding MSU crystals and gout. Our findings underscore the importance of SF crystal analysis in identifying the prevalence of crystals in the Mexican population. SF analysis provides for better diagnosis of crystal arthropathies and improves the quality of the medical care that the patient receives. Key Points • Synovial fluid analysis in laboratories from developing countries has been scarce. • In some cases, the initial diagnosis is modified after of synovial fluid analysis. • This study confirmed that synovial fluid analysis exhibits major diagnostic value for urate crystals and gout.

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.

Clinical implications of synovial fluid specimen handling for crystal associated arthritides: A systematic review

AIM

To identify the appropriate methods of synovial fluid (SF) specimen storage, manipulation and handling for crystal associated arthritides (CAA) diagnosis.

METHOD

A systematic literature review was conducted using 5 medical databases to identify diagnostic studies assessing SF specimen handling for calcium pyrophosphate (CPP) and monosodium urate (MSU) crystals identification. All included studies were rated for quality using the Quality Assessment of Diagnostic Accuracy Studies 2.

RESULTS

Fifteen studies, including 2 non-English language manuscripts, were included. Eight studies examined both types of crystals, while 3 studies examined CPP and 4 studies examined MSU crystals only. Overall, MSU crystals were more stable over time compared to CPP crystals. MSU stability was generally independent of time, preservative and temperature. CPP crystals deteriorated with time and were more stable if refrigerated. Ethylenediaminetetraacetic acid (EDTA) was a suitable preservative. Re-examining an initially negative SF sample at 24 hours facilitated detection of additional cases. Very few studies had an overall low risk of bias and applicability.

CONCLUSION

Monosodium urate crystals remain stable over time independent of storage time, temperature and preservative. CPP crystals are mostly stable for 24-48 hours but can deteriorate with time. Overall, SF crystal examination should ideally be done within 24-48 hours. They may be stored at room temperature without any preservative. Otherwise, refrigeration (4°C/39°F) and EDTA preservation is reasonable. Stored SF re-examination, at 24 hours, helps identify a small number of additional MSU and CPP cases. Centrifugation techniques allow better and easier crystal identification, particularly CPP. Most studies were of unclear or low quality.

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.

Tophaceous pseudogout in a 12-year-old dog, with a review of applicable laboratory tests

Pseudogout, also known as calcium pyrophosphate dihydrate (CPPD) deposition disease or chondrocalcinosis, is caused by crystalline deposits of CPPD within the extracellular matrix of articular hyaline cartilage and fibrocartilage, and within articular and periarticular connective tissue. Using a variety of laboratory techniques, we diagnosed pseudogout in the right hindlimb digit V of a 12-y-old Standard Poodle. Histologically, the joint, bone, tendon, and dermis were expanded and effaced by masses of mineralized, rhomboid crystals surrounded by macrophages, multinucleate giant cells, fibrous connective tissue, and chondroid and osseous matrix. Rhomboid crystals exhibiting weak-positive birefringence were identified under polarized light using a first-order red compensator filter. Scanning electron microscopy with energy-dispersive x-ray analysis (SEM-EDXA) revealed that the rhomboid crystals were composed of calcium, phosphorus, and oxygen. Fourier-transform infrared (FTIR) microspectroscopy confirmed the presence of calcium pyrophosphate. In dogs, tophaceous pseudogout, which was the variant of pseudogout in our case, occurs as a single, tumor-like periarticular mass that can be invasive and mimic neoplasia. Having ancillary confirmatory testing (SEM-EDXA and FTIR), particularly in unusual histologic scenarios, such as tophaceous pseudogout in dogs, is desirable for confirming the correct diagnosis, even though it is available only at certain reference centers. The pathogenesis of pseudogout is unknown.

Sonographic assessment of calcium pyrophosphate deposition disease at wrist. A focus on the dorsal scapho-lunate ligament

OBJECTIVES

To investigate the diagnostic accuracy of ultrasound and conventional radiography in the evaluation of calcium pyrophosphate crystal deposits at wrist level.

METHODS

Consecutive patients with a "definite" diagnosis of calcium pyrophosphate deposition disease and disease-controls were prospectively included in this cross-sectional single-centre study. Scapho-lunate ligament, triangular fibrocartilage complex, and volar recess of the radio-lunate joint were explored using ultrasound, conventional radiography and computed tomography.

RESULTS

Sixty one patients and 39 disease controls were enrolled. Two-hundred wrists were evaluated using both conventional radiography and ultrasound and 26 using computed tomography. Ultrasound findings indicative of crystal deposits were found in at least one wrist in 95.1% of patients and in 15.4% of controls (P<0.001). Scapho-lunate ligament calcifications were reported in 83.6% of patients and in 5.1% of controls (P<0.001). On conventional radiography, calcifications were found in at least one wrist in 72.1% of patients and in 0% of controls (P<0.001). Using the Ryan-McCarty criteria as a gold standard, sensitivity, specificity and diagnostic accuracy were 0.72 (0.59-0.83), 1.0 (0.91-1.0) and 0.83 (0.74-0.90) for conventional radiography and 0.95 (0.86-0.99), 0.85 (0.69-0.94) and 0.91 (0.84-0.96) for ultrasound. The agreement between ultrasound and computed tomography was substantial when assessing triangular fibrocartilage complex (kappa=0.70; 0.43-0.97) and scapho-lunate ligament (kappa=0.69; 0.41-0.97), and moderate for radio-lunate joint (kappa=0.46; 0.12-0.80).

CONCLUSIONS

This study supports the diagnostic accuracy of ultrasound in evaluating wrist involvement in calcium pyrophosphate deposition disease. The inclusion of the scapho-lunate ligament in a disease-oriented scanning protocol could improve the diagnostic performance of ultrasound.

Cartilage icing and chondrocalcinosis on knee radiographs in the differentiation between gout and calcium pyrophosphate deposition

Objective

To determine if findings of “cartilage icing" and chondrocalcinosis on knee radiography can differentiate between gout and calcium pyrophosphate deposition (CPPD).

Methods

IRB-approval was obtained and informed consent was waived for this retrospective study. Electronic medical records from over 2.3 million patients were searched for keywords to identify subjects with knee aspiration-proven cases of gout or CPPD. Radiographs were reviewed by two fellowship-trained musculoskeletal radiologists in randomized order, blinded to the patients’ diagnoses. Images were evaluated regarding the presence or absence of cartilage icing, chondrocalcinosis, tophi, gastrocnemius tendon calcification, and joint effusion. Descriptive statistics, sensitivity, specificity, positive and negative predictive values, and accuracy were calculated.

Results

From 49 knee radiographic studies in 46 subjects (31 males and 15 females; mean age 66±13 years), 39% (19/49) showed gout and 61% (30/49) CPPD on aspiration. On knee radiographs, cartilage icing showed a higher sensitivity for CPPD than gout (53–67% and 26%, respectively). Chondrocalcinosis also showed a higher sensitivity for CPPD than gout (50–57% versus 5%), with 95% specificity and 94% positive predictive value for diagnosis of CPPD versus gout. Soft tissue tophus-like opacities were present in gout at the patellar tendon (5%, 1/19) and at the popliteus groove in CPPD (15%, 4/27). Gastrocnemius tendon calcification was present in 30% (8/27) of subjects with CPPD, and 5% (1/19) of gout.

Conclusion

In subjects with joint aspiration-proven crystal disease of the knee, the radiographic finding of cartilage icing was seen in both gout and CPPD. Chondrocalcinosis (overall and hyaline cartilage) as well as gastrocnemius tendon calcification positively correlated with the diagnosis of CPPD over gout.

Rapid Gout Detection Method and Kit

Gout is a form of arthritis characterized by buildup of uric acid in synovial fluid, which causes severe swelling and can harm joints, tendons, and other tissues. It affects approximately 4% of the United States population, or approximately 8.3 million people nationwide and is therefore a topic of epidemiologic consideration due to its prevalence. Gout is typically diagnosed via polarized microscopy of arthroscopically-aspirated synovial fluid, which is a costly, time-consuming, labor-intensive, and technically complex procedure, warranting a simpler and less complex method for diagnosis. Here, we propose and validate a colorimetric method which is based on the ability of uric acid to reduce silver nitrate. We also assessed how the colorimetric change can be accelerated by changing the concentration of silver nitrate or adding different silver catalysts, as well as develop a matrix bed for improved handling and ease of use. When translated to the clinic, this diagnostic method for gout will have the potential to increase diagnostic efficiency and accelerate patient care at the bedside.

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.

Performance of the 2015 American College of Rheumatology/European League against Rheumatism Classification Criteria for Gout in Korean Patients with Acute Arthritis

BACKGROUND

We aimed to assess the performance of the 2015 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) classification criteria for gout in Korean patients with acute arthritis and to compare the performance of the ACR/EULAR criteria to that of other sets of criteria for gout classification.

METHODS

Patients with acute arthritis who underwent diagnostic arthrocentesis at one of the four participating rheumatology clinics were consecutively enrolled between February and December 2017. Crystal-proven gout was diagnosed upon confirming the presence of monosodium urate (MSU) crystals in patients with a clinical impression of gout as judged by the rheumatologist. The performance of the ACR/EULAR and other gout classification criteria, including the Rome, New York, American Rheumatism Association (ARA), Mexico, and Netherlands criteria, was analyzed regardless of the presence/absence of MSU crystals.

RESULTS

The study enrolled 118 gout patients (all crystal-proven) and 95 non-gout patients. According to the area under the curve, the diagnostic performance was the highest for the ACR/EULAR classification criteria (sensitivity, 80.5%; specificity, 95.8%; area under the curve, 0.966), followed by the Netherlands, Rome, ARA, New York, and Mexico criteria. All six sets of criteria demonstrated lower sensitivity in patients exhibiting the first episode of acute arthritis.

CONCLUSION

In Korean patients with acute arthritis, the ACR/EULAR classification criteria outperformed other sets of gout classification criteria even in the absence of information regarding the presence of MSU crystals. However, to enhance diagnostic sensitivity, synovial fluid analysis should be considered in patients with the first episode of acute arthritis.

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.

A Rare Case of Gout and Pseudogout Occurring in the Same Joint

Pseudogout and gout are common types of inflammatory joint disease in the elderly. However, the existence of both in a single joint in a patient is relatively rare. This case report describes an interesting case of a 42-year old man who presented with simultaneous gout and pseudogout in the knee joint, diagnosed via polarised light microscopy. There was no radiographic evidence of pseudogout. This case report serves to illustrate the need to actively exclude concomitant pseudogout, especially in patients suffering from recurrent attacks of gout.

[Synovial fluid cytodiagnosis]

Synovial fluid samples represent only a very small percentage of routine work in a cytology laboratory. However, its microscopic examination allows us to observe different types of cells, particles and structures that, due to their morphological characteristics, may provide relevant data for cytodiagnosis. We present certain aspects related to arthrocentesis, the relationship between the gross appearance of synovial fluid and certain pathological processes, as well as the different techniques for processing and staining the smears. Furthermore, we describe the main cytological findings in various pathological conditions of the synovial joints, such as infections (bacterial and fungal), non-infectious inflammatory type (osteoarthrosis, rheumatoid arthritis, connective tissue diseases) and tumoral, distinguishing between primary and metastatic, both solid and haematological neoplasms.

Painless gouty tophus in the nasal bridge: A case report and literature review

RATIONALE

A gouty tophus, arising from the deposition of monosodium urate crystals (MSU), rarely occurs in the nasal bridge. There have been only 7 documented cases of a gouty tophus in the nasal bridge from 1978 to 2018 in English-language literature.

PATIENT CONCERNS

A 65-year-old male had a chief complaint of a lump in the nasal bridge that was slowly growing for over 1 year.

DIAGNOSIS

MSU crystals were confirmed through ultrasonography (US) and pathological examinations.

INTERVENTIONS

A cosmetically less destructive method, ultrasound-guided fine needle aspiration cytology (FNAC) was used to approach the mass lesion of nasal bridge.

OUTCOMES

The diagnosis was confirmed as a gouty tophus without performing a nasal subdermal exploration.

LESSONS

This case report is the first use of US with FNAC to approach and diagnosed a gouty tophus in the nasal bridge.

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.

Gouty arthritis: decision-making following dual-energy CT scan in clinical practice, a retrospective analysis

To establish whether dual-energy CT (DECT) is a diagnostic tool, i.e., associated with initiation or discontinuation of a urate lowering drug (ULD). Secondly, to determine whether DECT results (gout deposition y/n) can be predicted by clinical and laboratory variables. Digital medical records of 147 consecutive patients with clinical suspicion of gout were analyzed retrospectively. Clinical data including medication before and after DECT, lab results, and results from diagnostic joint aspiration and DECT were collected. The relationship between DECT results and clinical and laboratory results was evaluated by univariate regression analyses; predictors showing a p < 0.10 were entered in a multivariate logistic regression model with the DECT result as outcome variable. A backward stepwise technique was applied. After the DECT, 104 of these patients had a clinical diagnosis of gout based on the clinical judgment of the rheumatologist, and in 84 of these patients, the diagnosis was confirmed by demonstration of monosodium urate (MSU) crystals in synovial fluid (SF) or by positive DECT. After DECT, the current ULD was modified in 33 (22.4%) of patients; in 29 of them, ULD was started and in 1 it was intensified. Following DECT, the current ULD was stopped in three patients. In the multivariable regression model, cardiovascular disease (OR 3.07, 95% CI 1.26-7.47), disease duration (OR 1.008, 95% CI 1.001-1.016), frequency of attack (OR 1.23, 95% CI 1.07-1.42), and creatinine clearance (OR 2.03, 95% CI 0.91-1.00) were independently associated with positive DECT results. We found that the DECT result increases the confidence of the prescribers in their decision to initiation or discontinuation of urate lowering therapy regimen in of mono- or oligoarthritis. It may be a useful imaging tool for patients who cannot undergo joint aspiration because of contraindications or with difficult to aspirate joints, or those who refuse joint aspiration. We also suggest the use of DECT in cases where a definitive diagnosis cannot be made from signs, symptoms, and MSU analysis alone.

The added value of synovial fluid centrifugation for monosodium urate and calcium pyrophosphate crystal detection

The aim of the study was to assess the added value of synovial fluid (SF) centrifugation for microscopic monosodium urate (MSU) and calcium pyrophosphate (CPP) crystal detection in patients with arthritis. This is a prospective observational study using SF samples from joints of patients undergoing joint arthrocentesis. Two blinded observers assessed the SF smears by polarized light microscopy for the presence of crystals before as well as after centrifugation. SF samples were collected from 98 patients with arthritis. After exclusion, 87 samples were eligible for inclusion. Of each sample, 2 smears before and after centrifugation were prepared and microscopically examined, resulting in 348 smears per observer. Observer 1 identified MSU crystals in 18.4% and CPP in 9.2% of the smears before as well as after centrifugation. No extra MSU crystal-positive smears were identified after centrifugation. However, centrifugation yielded 4 additional CPP crystal-positive smears. Observer 2 identified MSU crystals in 15.5% and CPP crystals in 6.3% of the smears before as well as after centrifugation. Centrifugation yielded 2 additional MSU crystal-positive smears and 4 CPP crystal-positive smears. Monosodium urate crystals were well recognized without centrifugation. Centrifugation of SF had limited additional value for increasing the amount of MSU-positive smears. However, CPP crystals were identified in a higher number of smears after centrifugation than before. Therefore, centrifugation may be of additional value in selected patients with suspected calcium pyrophosphate deposition disease and to a lesser extent for gout.