Performance of classification criteria for gout in early and established disease

Multiple gouty tophi in the head and neck with normal serum uric acid: A case report and review of literatures

BACKGROUND

Gouty tophus is rarely reported in the head and neck areas. To the best of our knowledge, this is the first report on multiple gouty tophi in the head and neck with normal serum uric acid (SUA) levels.

CASE SUMMARY

We report a case of multiple gouty tophi in the nasal dorsal and auricle regions with normal SUA levels. The patient was admitted to the hospital with a chief complaint of recurrent nasal swelling and pain for 3 years, which was aggravated for 3 d. The patient’s SUA level had been regularly reviewed in the outpatient department and had been successfully controlled for several years. Resection of the nasal masses was performed. Cartilage from the right ear cavity was used to repair the nasal defects. The pathological report confirmed a nasal gouty tophus. No recurrence or deformity was found after a 1 year follow-up.

CONCLUSION

Normal SUA cannot completely negate the diagnosis of gouty tophus, especially in some rare regions.

Ultrasound for the diagnosis of gout-the value of gout lesions as defined by the Outcome Measures in Rheumatology ultrasound group

OBJECTIVE

To evaluate ultrasound for diagnosing gout using consensus-based Outcome Measures in Rheumatology ultrasound definitions of gout lesions.

METHODS

Ultrasound was performed in patients with clinically suspected gout. Joints (28) and tendons (26) were binarily evaluated for the Outcome Measures in Rheumatology gout lesions-double contour (DC), tophus, aggregates and erosions. Ultrasound assessment was compared with two reference standards: (i) presence of MSU crystals in joint/tophus aspirate (primary outcome) and (ii) ACR/EULAR 2015 gout classification criteria (secondary outcome). Both reference standards were evaluated by rheumatologists blinded to ultrasound findings. Sensitivity, specificity, accuracy, positive predictive value and negative predictive value of each ultrasound lesion against both reference standards were determined.

RESULTS

Eighty-two patients (70 men), mean age 62.4 (range 19-88) years, were included. Fifty-seven patients were MSU-positive whereas 25 patients were MSU-negative (no MSU crystals: 23; aspiration unsuccessful: 2). Of these 25 patients, three patients were classified as ACR/EULAR-positive (i.e. totally 60 ACR/EULAR-positive patients). All ultrasound lesions had high sensitivities for gout (0.77-0.95). DC and tophus showed high specificities (0.88-0.95), positive predictive values (0.94-0.98) and accuracies (0.82-0.84) when both reference standards were used. In contrast, low specificities were found for aggregates and erosions (0.32-0.59). Ultrasound of MTP joints for DC or tophus, knee joint for DC and peroneus tendons for tophus was sufficient to identify all MSU-positive patients with ultrasound signs of gout at any location.

CONCLUSION

Ultrasound-visualized DC and tophus, as defined by the Outcome Measures in Rheumatology ultrasound group, show high specificities, positive predictive values and accuracies for diagnosing gout and are therefore valid tools in clinical practice.

Dual-energy CT in gout patients: Do all colour-coded lesions actually represent monosodium urate crystals?

BACKGROUND

Dual-energy CT (DECT) can acknowledge differences in tissue compositions and can colour-code tissues with specific features including monosodium urate (MSU) crystals. However, when evaluating gout patients, DECT frequently colour-codes material not truly representing MSU crystals and this might lead to misinterpretations. The characteristics of and variations in properties of colour-coded DECT lesions in gout patients have not yet been systematically investigated. The objective of this study was to evaluate the properties and locations of colour-coded DECT lesions in gout patients.

METHODS

DECT of the hands, knees and feet were performed in patients with suspected gout using factory default gout settings, and colour-coded DECT lesions were registered. For each lesion, properties [mean density (mean of Hounsfield Units (HU) at 80 kV and Sn150kV), mean DECT ratio and size] and location were determined. Subgroup analysis was performed post hoc evaluating differences in locations of lesions when divided into definite MSU depositions and possibly other lesions.

RESULTS

In total, 4033 lesions were registered in 27 patients (23 gout patients, 3918 lesions; 4 non-gout patients, 115 lesions). In gout patients, lesions had a median density of 160.6 HU and median size of 6 voxels, and DECT ratios showed an approximated normal distribution (mean 1.06, SD 0.10), but with a right heavy tail consistent with the presence of smaller amounts of high effective atomic number lesions (e.g. calcium-containing lesions). The most common locations of lesions were 1st metatarsophalangeal (MTP1), knee and midtarsal joints along with quadriceps and patella tendons. Subgroup analyses showed that definite MSU depositions (large volume, low DECT ratio, high density) had a similar distribution pattern, whereas possible calcium-containing material (high DECT ratio) and non-gout MSU-imitating lesions (properties as definite MSU depositions in non-gout patients) were primarily found in some larger joints (knee, midtarsal and talocrural) and tendons (Achilles and quadriceps). MTP1 joints and patella tendons showed only definite MSU depositions.

CONCLUSION

Colour-coded DECT lesions in gout patients showed heterogeneity in properties and distribution. MTP1 joints and patella tendons exclusively showed definite MSU depositions. Hence, a sole focus on these regions in the evaluation of gout patients may improve the specificity of DECT scans.

[Gout]

Gout is a chronic disease due to the deposition of monosodium urate microcrystals in joints and tissues. Its incidence and prevalence are increasing worldwide in close relation with the epidemic of obesity and metabolic syndrome. Gout is related to chronic hyperuricemia that should be treated to ensure the reduction or even the disappearance of acute attacks ("gout flares") and to reduce the size and number of tophi. If arthritis of the first metatarsophalangeal joint is the most typical form, other joints may be affected, including the spine. Demonstration of urate microcrystals arthritis allows diagnosis of gout but, in the absence of possibility of performing joint puncture, imaging may be useful for providing complementary diagnostic elements. Appropriate care is essential to reduce the number of flares and the evolution towards gouty arthropathy but also in terms of public health in order to reduce costs related to this pathology.

Gout: state of the art after a decade of developments

This review article summarizes the relevant English literature on gout from 2010 through April 2017. It emphasizes that the current epidemiology of gout indicates a rising prevalence worldwide, not only in Western countries but also in Southeast Asia, in close relationship with the obesity and metabolic syndrome epidemics. New pathogenic mechanisms of chronic hyperuricaemia focus on the gut (microbiota, ABCG2 expression) after the kidney. Cardiovascular and renal comorbidities are the key points to consider in terms of management. New imaging tools are available, including US with key features and dual-energy CT rendering it able to reveal deposits of urate crystals. These deposits are now included in new diagnostic and classification criteria. Overall, half of the patients with gout are readily treated with allopurinol, the recommended xanthine oxidase inhibitor (XOI), with prophylaxis for flares with low-dose daily colchicine. The main management issues are related to patient adherence, because gout patients have the lowest rate of medication possession ratio at 1 year, but they also include clinical inertia by physicians, meaning XOI dosage is not titrated according to regular serum uric acid level measurements for targeting serum uric acid levels for uncomplicated (6.0 mg/dl) and complicated gout, or the British Society for Rheumatology recommended target (5.0 mg/dl). Difficult-to-treat gout encompasses polyarticular flares, and mostly patients with comorbidities, renal or heart failure, leading to contraindications or side effects of standard-of-care drugs (colchicine, NSAIDs, oral steroids) for flares; and tophaceous and/or destructive arthropathies, leading to switching between XOIs (febuxostat) or to combining XOI and uricosurics.

Gout

Gout is a chronic disease caused by monosodium urate (MSU) crystal deposition. Gout typically presents as an acute, self-limiting inflammatory monoarthritis that affects the joints of the lower limb. Elevated serum urate level (hyperuricaemia) is the major risk factor for MSU crystal deposition and development of gout. Although traditionally considered a disorder of purine metabolism, altered urate transport, both in the gut and the kidneys, has a key role in the pathogenesis of hyperuricaemia. Anti-inflammatory agents, such corticosteroids, NSAIDs and colchicine, are widely used for the treatment of gout flare; recognition of the importance of NLRP3 inflammasome activation and bioactive IL-1β release in initiation of the gout flare has led to the development of anti-IL-1β biological therapy for gout flares. Sustained reduction in serum urate levels using urate-lowering therapy is vital in the long-term management of gout, which aims to dissolve MSU crystals, suppress gout flares and resolve tophi. Allopurinol is the first-line urate-lowering therapy and should be started at a low dose, with gradual dose escalation. Low-dose anti-inflammatory therapies can reduce gout flares during initiation of urate-lowering therapy. Models of care, such as nurse-led strategies that focus on patient engagement and education, substantially improve clinical outcomes and now represent best practice for gout management.

2018 updated European League Against Rheumatism evidence-based recommendations for the diagnosis of gout

Although gout is the most common inflammatory arthritis, it is still frequently misdiagnosed. New data on imaging and clinical diagnosis have become available since the first EULAR recommendations for the diagnosis of gout in 2006. This prompted a systematic review and update of the 2006 recommendations. A systematic review of the literature concerning all aspects of gout diagnosis was performed. Recommendations were formulated using a Delphi consensus approach. Eight key recommendations were generated. A search for crystals in synovial fluid or tophus aspirates is recommended in every person with suspected gout, because demonstration of monosodium urate (MSU) crystals allows a definite diagnosis of gout. There was consensus that a number of suggestive clinical features support a clinical diagnosis of gout. These are monoarticular involvement of a foot or ankle joint (especially the first metatarsophalangeal joint); previous episodes of similar acute arthritis; rapid onset of severe pain and swelling; erythema; male gender and associated cardiovascular diseases and hyperuricaemia. When crystal identification is not possible, it is recommended that any atypical presentation should be investigated by imaging, in particular with ultrasound to seek features suggestive of MSU crystal deposition (double contour sign and tophi). There was consensus that a diagnosis of gout should not be based on the presence of hyperuricaemia alone. There was also a strong recommendation that all people with gout should be systematically assessed for presence of associated comorbidities and risk factors for cardiovascular disease, as well as for risk factors for chronic hyperuricaemia. Eight updated, evidence-based, expert consensus recommendations for the diagnosis of gout are proposed.

The Validity of Gout Diagnosis in Primary Care: Results from a Patient Survey

OBJECTIVE

Validate primary care diagnosis of gout by the Mexico and the Netherlands classification criteria.

METHODS

Questionnaires on gout characteristics were sent to all individuals aged ≥ 18 with ≥ 1 International Classification of Diseases, 10th ed. diagnosis of gout at 12 primary care centers.

RESULTS

Positive predictive values for gout diagnosis ranged from 71% for the Netherlands criteria to 80% for the Mexico criteria. Maximum inflammation within 24 h was the most common reported symptom (86%).

CONCLUSION

The vast majority of gout cases in primary care fulfill classification criteria and are valid for research purposes.

Serum/Synovial Fluid Urate Ratio as an Indicator for Distinguishing Gouty Arthritis From Other Arthritides

Objectives

This study aims to compare the serum/synovial fluid (SF) urate ratio of gouty arthritis and other arthritides and investigate whether this ratio may be an indicator for distinguishing gouty arthritis from other arthritides.

Patients and methods

Paired serum and SF samples from 70 patients (38 males, 32 females; mean age 57.9 years; range, 27.5 to 78.4 years) comprised of 20 patients with gout, 20 patients with rheumatoid arthritis and 30 patients with osteoarthritis were collected simultaneously for urate measurement. Patient data were recorded including demographic data (age, sex), body mass index, estimated glomerular filtration rate, comorbidities (diabetes, hypertension and dyslipidemia), disease duration (from the first symptoms), pain duration before arthrocentesis at this time, presence of tophi or not, serum albumin, erythrocyte sedimentation rate, C-reactive protein and SF white blood cell count.

Results

Gout patients had highest levels of urate in both serum and SF among the three groups (p<0.001). The serum/SF urate ratio of gout patients was significantly lower among the three groups (p<0.001). Receiver-operating characteristic curve analysis demonstrated that serum/SF urate ratio can predict the extent of gouty arthritis (the value of area under the curve was 0.867, p<0.001).

Conclusion

Serum/SF urate ratio may be an indicator for distinguishing gouty arthritis from other arthritides.

Burden of gout in the Nordic region, 1990-2015: findings from the Global Burden of Disease Study 2015

OBJECTIVE

To explore the burden of gout in the Nordic region, with a population around 27 million in 2015 distributed across six countries.

METHOD

We used the findings of the 2015 Global Burden of Diseases study to report prevalence and disability associated with gout in the Nordic region.

RESULTS

From 1990 to 2015, the number of prevalent gout cases rose by 30% to 252 967 [95% uncertainty interval (UI) 223 478‒287 288] in the Nordic region. In 2015, gout contributed to 7982 (95% UI 5431‒10 800) years lived with disability (YLDs) in the region, an increase of 29% (95% UI 24‒35%) from 1990. While the crude YLD rate of gout increased by 12.9% (95% UI 7.8‒18.1%) between 1990 and 2015, the age-standardized YLD rate remained stable. Gout was ranked as the 63rd leading cause of total YLDs in the region in 2015, with the highest rank in men aged 55-59 years (38th leading cause of YLDs). The corresponding rank at the global level was 94. Of 195 countries studied, four Nordic countries [Greenland (2nd), Iceland (12th), Finland (14th), and Sweden (15th)] were among the top 15 countries with the highest age-standardized YLD rate of gout.

CONCLUSION

The burden of gout is rising in the Nordic region. Gout's contribution to the total burden of diseases in the region is more significant than the global average. Expected increases in gout burden owing to population growth and ageing call for stronger preventive and therapeutic strategies for gout management in Nordic countries.

Gout Classification Criteria: Update and Implications

Gout is the most common inflammatory arthritis, with a rising prevalence and incidence worldwide. There has been a resurgence in gout research, fueled, in part, by a number of advances in pharmacologic therapy for gout. The conduct of clinical trials and other observational research in gout requires a standardized and validated means of assembling well-defined groups of patients with gout for such research purposes. Recently, an international collaborative effort that involved a data-driven process with state-of-the art methodology supported by the American College of Rheumatology and the European League Against Rheumatism led to publication of new gout classification criteria.

Performance of Ultrasound in the Diagnosis of Gout in a Multicenter Study: Comparison With Monosodium Urate Monohydrate Crystal Analysis as the Gold Standard

OBJECTIVE

To examine the performance of ultrasound (US) for the diagnosis of gout using the presence of monosodium urate monohydrate (MSU) crystals as the gold standard.

METHODS

We analyzed data from the Study for Updated Gout Classification Criteria (SUGAR), a large, multicenter observational cross-sectional study of consecutive subjects with at least 1 swollen joint who conceivably may have gout. All subjects underwent arthrocentesis; cases were subjects with confirmed MSU crystals. Rheumatologists or radiologists who were blinded with regard to the results of the MSU crystal analysis performed US on 1 or more clinically affected joints. US findings of interest were double contour sign, tophus, and snowstorm appearance. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Multivariable logistic regression models were used to examine factors associated with positive US results among subjects with gout.

RESULTS

US was performed in 824 subjects (416 cases and 408 controls). The sensitivity, specificity, PPV, and NPV for the presence of any 1 of the features were 76.9%, 84.3%, 83.3%, and 78.2%, respectively. Sensitivity was higher among subjects with a disease duration of ≥2 years and among subjects with subcutaneous nodules on examination (suspected tophus). Associations with a positive US finding included suspected clinical tophus (odds ratio [OR] 4.77 [95% confidence interval (95% CI) 2.23-10.21]), any abnormality on plain radiography (OR 4.68 [95% CI 2.68-8.17]), and serum urate level (OR 1.31 [95% CI 1.06-1.62]).

CONCLUSION

US features of MSU crystal deposition had high specificity and high PPV but more limited sensitivity for early gout. The specificity remained high in subjects with early disease and without clinical signs of tophi.

Critical revision of the medical treatment of gout in Brazil

Gout is considered the most common form of inflammatory arthritis in men over 40 years. The authors present a brief review of the current treatment of gout and discuss the existing pharmacological limitations in Brazil for the treatment of this disease. Although allopurinol is still the main drug administered for decreasing serum levels of uric acid in gout patients in this country, the authors also present data that show a great opportunity for the Brazilian drug market for the treatment of hyperuricemia and gout and especially for patients using private and public (SUS) health care systems.

[Gout - new approaches to diagnostics and treatment]

An attack of gout is extremely painful. Recurrent attacks of arthritis in one or more joints or tendon sheaths accompanied by intense pain are typical of this commonly occurring condition. As these symptoms indicate acute inflammation due to uric acid crystal deposition, good diagnostics are essential to enable initiation of drug treatment which removes the crystals deposited in tissue.

Survey Definitions of Gout for Epidemiologic Studies: Comparison With Crystal Identification as the Gold Standard

OBJECTIVE

To identify the best-performing survey definition of gout from items commonly available in epidemiologic studies.

METHODS

Survey definitions of gout were identified from 34 epidemiologic studies contributing to the Global Urate Genetics Consortium (GUGC) genome-wide association study. Data from the Study for Updated Gout Classification Criteria (SUGAR) were randomly divided into development and test data sets. A data-driven case definition was formed using logistic regression in the development data set. This definition, along with definitions used in GUGC studies and the 2015 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) gout classification criteria were applied to the test data set, using monosodium urate crystal identification as the gold standard.

RESULTS

For all tested GUGC definitions, the simple definition of "self-report of gout or urate-lowering therapy use" had the best test performance characteristics (sensitivity 82%, specificity 72%). The simple definition had similar performance to a SUGAR data-driven case definition with 5 weighted items: self-report, self-report of doctor diagnosis, colchicine use, urate-lowering therapy use, and hyperuricemia (sensitivity 87%, specificity 70%). Both of these definitions performed better than the 1977 American Rheumatism Association survey criteria (sensitivity 82%, specificity 67%). Of all tested definitions, the 2015 ACR/EULAR criteria had the best performance (sensitivity 92%, specificity 89%).

CONCLUSION

A simple definition of "self-report of gout or urate-lowering therapy use" has the best test performance characteristics of existing definitions that use routinely available data. A more complex combination of features is more sensitive, but still lacks good specificity. If a more accurate case definition is required for a particular study, the 2015 ACR/EULAR gout classification criteria should be considered.

Performance of the Existing Classification Criteria for Gout in Thai Patients Presenting With Acute Arthritis

Currently, there are 5 existing classification criteria for gout: the Rome, New York, American Rheumatism Association (ARA), Mexico, and Netherlands criteria. This study was carried out to determine the performance of these classification criteria in Thai patients presenting with acute arthritis.All consecutive patients presenting with acute arthritis and being consulted at the Rheumatology Unit, Chiang Mai University Hospital from January 2013 to May 2015 were invited to join the study. Gout was defined by the presence of monosodium urate crystals in the synovial fluid or tissue examined by experienced rheumatologists. The 5 existing gout classification criteria were performed and evaluated in all of the patients, who were divided in subgroups of early disease (≤2 years), established disease (>2 years), and those without tophus.There were 136 gout and 97 nongout patients. Sensitivity and specificity across all criteria ranged from 75.7% to 97.1% and 68.0% to 84.5%, respectively. Overall, the Mexico criteria had the highest sensitivity (97.1%), and the ARA survey criteria the highest specificity (84.5%), whereas the Mexico criteria performed well in early disease with sensitivity and specificity of 97.1% and 81.7%, respectively. All 5 criteria showed high sensitivity (from 76.4% to 99.1%) but low specificity (from 30.8% to 65.4%) in established disease. In patients without tophus, the sensitivity and specificity ranged from 64.1% to 95.7% and 68.8% to 85.4%, respectively. The ARA survey criteria across all groups showed consistently high specificity for gout.The 5 existing classification criteria for gout had limited sensitivity and specificity in Thai patients presenting with acute arthritis. The ARA survey criteria are the most suitable for diagnosing gout in Thai people when crystal identification is not available.

Epidemiology and health-related services

PURPOSE OF REVIEW

This article presents recent epidemiologic contributions focusing on gout-related conditions, especially if controversial, to find plausible, despite hypothetical, mechanistic explanations from the clinician perspective.

RECENT FINDINGS

The prevalence of gout is increasing, but it is only partially clear that the incidence may be increasing as well. Direct associations of gout with increased risk of diabetes, black races, neurodegenerative disorders, and sugar-enriched foods have been recently questioned. A negative association with smoking has been reported, and new evidence shows that the impact of diet may be independent of obesity. Kidney disease and diuretics have been confirmed to be associated with gout, whereas new data on aging and menopause have come to challenge apparently established disease mechanisms. Regarding treatments, increase in bladder cancer associated with chronic allopurinol use has been reported, and the positive effect of urate-lowering treatment on cardiovascular events has been contested.

SUMMARY

Epidemiological data in gout-related conditions are still evolving and claim for future cohort or intervention studies to prove causality. Controversies in epidemiological results fertilize the ground for studies to prove mechanisms and causality and provides a unique opportunity for clinical intervention to improve outcomes, especially with regard to treatments.

2015 Gout classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative

Objective

Existing criteria for the classification of gout have suboptimal sensitivity and/or specificity, and were developed at a time when advanced imaging was not available. The current effort was undertaken to develop new classification criteria for gout.

Methods

An international group of investigators, supported by the American College of Rheumatology and the European League Against Rheumatism, conducted a systematic review of the literature on advanced imaging of gout, a diagnostic study in which the presence of monosodium urate monohydrate (MSU) crystals in synovial fluid or tophus was the gold standard, a ranking exercise of paper patient cases, and a multi-criterion decision analysis exercise. These data formed the basis for developing the classification criteria, which were tested in an independent data set.

Results

The entry criterion for the new classification criteria requires the occurrence of at least one episode of peripheral joint or bursal swelling, pain, or tenderness. The presence of MSU crystals in a symptomatic joint/bursa (ie, synovial fluid) or in a tophus is a sufficient criterion for classification of the subject as having gout, and does not require further scoring. The domains of the new classification criteria include clinical (pattern of joint/bursa involvement, characteristics and time course of symptomatic episodes), laboratory (serum urate, MSU-negative synovial fluid aspirate), and imaging (double-contour sign on ultrasound or urate on dual-energy CT, radiographic gout-related erosion). The sensitivity and specificity of the criteria are high (92% and 89%, respectively).

Conclusions

The new classification criteria, developed using a data-driven and decision-analytic approach, have excellent performance characteristics and incorporate current state-of-the-art evidence regarding gout.

Prevalence of Hyperuricemia and Gout in Mainland China from 2000 to 2014: A Systematic Review and Meta-Analysis

We systematically identified the prevalence of hyperuricemia and gout in mainland China and provided informative data that can be used to create appropriate local public health policies. Relevant articles from 2000 to 2014 were identified by searching 5 electronic databases: PubMed, Google Scholar, Chinese Wanfang, CNKI, and Chongqing VIP. All of the calculations were performed using the Stata 11.0 and SPSS 20.0 software. The eligible articles (n = 36; 3 in English and 33 in Chinese) included 44 studies (38 regarding hyperuricemia and 6 regarding gout). The pooled prevalence of hyperuricemia and gout was 13.3% (95% CI: 11.9%, 14.6%) and 1.1% (95% CI: 0.7%, 1.5%), respectively. Although publication bias was observed, the results did not change after a trim and fill test, indicating that that impact of this bias was likely insignificant. The prevalence of hyperuricemia and gout was high in mainland China. The subgroup analysis suggested that the geographical region, whether the residents dwell in urban or rural and coastal or inland areas, the economic level, and sex may be associated with prevalence.

A prospective evaluation of ultrasound as a diagnostic tool in acute microcrystalline arthritis

INTRODUCTION

The performance of ultrasound (US) in the diagnosis of acute gouty (MSU) arthritis and calcium pyrophosphate (CPP) arthritis is not yet well defined. Most studies evaluated US as the basis for diagnosing crystal arthritis in already diagnosed cases of gout and few prospective studies have been performed.

METHODS

One hundred nine consecutive patients who presented an acute arthritis of suspected microcrystalline arthritis were prospectively included. All underwent an US of the symptomatic joints(s) and of knees, ankles and 1(st) metatarsopalangeal (MTP) joints by a rheumatologist "blinded" to the clinical history. 92 also had standard X-rays. Crystal identification was the gold standard.

RESULTS

Fifty-one patients had MSU, 28 CPP and 9 had both crystals by microscopic analysis. No crystals were detected in 21. One had septic arthritis. Based on US signs in the symptomatic joint, the sensitivity of US for both gout and CPP was low (60% for both). In gout, the presence of US signs in the symptomatic joint was highly predictive of the diagnosis (PPV = 92%). When US diagnosis was based on an examination of multiple joints, the sensitivity for both gout and CPP rose significantly but the specificity and the PPV decreased. In the absence of US signs in all the joints studied, CPP arthritis was unlikely (NPV = 87%) particularly in patients with no previous crisis (NPV = 94%). X-ray of the symptomatic joints was confirmed to be not useful in diagnosing gout and was equally sensitive or specific as US in CPP arthritis.

CONCLUSIONS

Arthrocenthesis remains the key investigation for the diagnosis of microcrystalline acute arthritis. Although US can help in the diagnostic process, its diagnostic performance is only moderate. US should not be limited to the symptomatic joint. Examination of multiple joints gives a better diagnostic sensitivity but lower specificity.

The use and abuse of diagnostic/classification criteria

In rheumatic diseases, classification criteria have been developed to identify well-defined homogenous cohorts for clinical research. Although they are commonly used in clinical practice, their use may not be appropriate for routine diagnostic clinical care. Classification criteria are being revised with improved methodology and further understanding of disease pathophysiology, but they still may not encompass all unique clinical situations to be applied for diagnosis of heterogenous, rare, evolving rheumatic diseases. Diagnostic criteria development is challenging primarily due to difficulty for universal application given significant differences in the prevalence of rheumatic diseases based on geographical area and clinic settings. Despite these shortcomings, the clinician can still use classification criteria for understanding the disease as well as a guide for diagnosis with a few caveats. We present the limits of current classification criteria, their use and abuse in clinical practice, and how they should be used with caution when applied in clinics.