Magnetic resonance imaging in the quantitative assessment of gouty tophi

Glossary of terms for musculoskeletal radiology

Members of the International Skeletal Society compiled a glossary of terms for musculoskeletal radiology. The authors also represent national radiology or pathology societies in Asia, Australia, Europe, and the USA. We provide brief descriptions of musculoskeletal structures, disease processes, and syndromes and address their imaging features. Given the abundance of musculoskeletal disorders and derangements, we chose to omit most terms relating to neoplasm, spine, intervention, and pediatrics. Consensus agreement was obtained from 19 musculoskeletal radiology societies worldwide.

Imaging tools to measure treatment response in gout

Imaging tests are in clinical use for diagnosis, assessment of disease severity and as a marker of treatment response in people with gout. Various imaging tests have differing properties for assessing the three key disease domains in gout: urate deposition (including tophus burden), joint inflammation and structural joint damage. Dual-energy CT allows measurement of urate deposition and bone damage, and ultrasonography allows assessment of all three domains. Scoring systems have been described that allow radiological quantification of disease severity and these scoring systems may play a role in assessing the response to treatment in gout. This article reviews the properties of imaging tests, describes the available scoring systems for quantification of disease severity and discusses the challenges and controversies regarding the use of imaging tools to measure treatment response in gout.

Imaging as a potential outcome measure in gout studies: A systematic literature review

OBJECTIVE

Despite major progress in the imaging of gout, it is unclear which domains these techniques can evaluate and whether imaging modalities have the potential to provide valid outcome measures. The aim of this study was to assess the use of imaging instruments in gout according to the Outcomes in Rheumatology Clinical Trials (OMERACT) filter to inform the development of imaging as an outcome measure.

METHODS

A systematic literature search of imaging modalities for gout was undertaken. Articles were assessed by two reviewers to identify imaging domains and summarize information according to the OMERACT filter.

RESULTS

The search identified 78 articles (one abstract). Modalities included were conventional radiography (CR) (16 articles), ultrasound (US) (29), conventional computed tomography (CT) (11), dual energy computed tomography (DECT) (20), and magnetic resonance imaging (MRI) (16). Three domains were identified as follows: urate deposition, joint damage, and inflammation. Although sufficient data were available to assess feasibility, validity, and reliability, comprehensive assessment of discrimination was not possible due to the paucity of prospective imaging studies. CR is widely accessible, inexpensive with a validated damage scoring system. US and MRI offer radiation-free methods of evaluating urate deposition, damage and inflammation, but may be limited by accessibility. DECT provides excellent definition of urate deposition and bone damage, but has restricted availability and requires radiation.

CONCLUSIONS

Imaging methods can detect urate deposition, damage, and inflammation in gout. More than one modality may be required depending on the domains and therapeutic agent of interest. No single imaging method currently fulfils all aspects of the OMERACT filter for any domain.

Imaging of gout: New tools and biomarkers?

While joint aspiration and crystal identification by polarizing microscopy remain the gold standard for diagnosing tophaceous gout, agreement among medical and ancillary health personnel examining synovial fluid using polarizing microscopy for the detection of monosodium urate (MSU) crystals appears to be poor. Imaging modalities, including conventional radiography (CR), ultrasonography (US), magnetic resonance imaging (MRI), and dual-energy computed tomography (DECT), have been found to provide information on the deposition of MSU crystals in tissues, and the consequences of such deposition. CR can demonstrate typical "punched out lesions" with marginal overhangs, but the sensitivity for erosion detection is better for DECT and US. US is inexpensive and can identify tophus deposition in and around joints, erosions, and tissue inflammation if power Doppler US is used. MRI can show tophi, bone marrow edema, and inflammation, but MRI findings of tophi may be nonspecific. DECT can identify and color-code tophaceous material, and provide an overview of the tophus burden of a joint area. Because of the lower number of available studies, the strength of evidence for the newer imaging can be improved through further research.

Relevant aspects of imaging in the diagnosis and management of gout

Gout is an inflammatory arthritis characterized by the deposition of monosodium urate crystals in the synovial membrane, articular cartilage and periarticular tissues leading to inflammation. Men are more commonly affected, mainly after the 5th decade of life. Its incidence has been growing with the population aging. In the majority of the cases, the diagnosis is made by clinical criteria and synovial fluid analysis, in search for monosodium urate crystals. Nonetheless, gout may sometimes have atypical presentations, complicating the diagnosis. In these situations, imaging methods have a fundamental role, aiding in the diagnostic confirmation or excluding other possible differential diagnosis. Conventional radiographs are still the most commonly used method in gout patients' evaluation; nevertheless, this is not a sensitive method, since it detect only late alterations. In the last years, there have been several advances in imaging methods for gout patients. Ultrasound has shown a great accuracy in the diagnosis of gout, identifying monosodium urate deposits in the synovial membrane and articular cartilage, in detecting and characterizing tophi and in identifying tophaceous tendinopathy and enthesopathy. Ultrasound has also been able to show crystal deposition in patients with articular pain in the absence of a classical gout crisis. Computed tomography is an excellent method for detecting bone erosions, being useful in spine involvement. Dual-energy CT is a new method able to provide information about the chemical composition of tissues, with high accuracy in the identification of monosodium urate deposits, even in the early stages of the disease and in cases of difficult characterization. Magnetic resonance imaging is useful in the evaluation of deep tissues not accessible by ultrasound. Besides the diagnosis, with the emergence of new drugs that aim to reduce tophaceous burden, imaging methods have become useful tools in monitoring the treatment of patients with gout.

Dual energy computed tomography: a novel technique for diagnosis of gout

AIM

To evaluate the sensitivity and specificity of dual energy computed tomography (DECT) for diagnosing gout compared with a composite gold standard (CGS) comprising joint aspiration and/or American College of Rheumatology clinico-radiographic criteria.

METHODS

Ninety patients of suspected gout underwent radiography and DECT of bilateral feet and knees. Radiographs and non-contrast CT (NCCT) were assessed for morphological characteristics, following which DECT was used to identify urate deposits.

RESULTS

With CGS as a reference (n = 90), sensitivity of radiographs was 15% (95% confidence interval [CI]: 6-27%) while specificity was 100% (95% CI: 90-100%). Sensitivity of NCCT was 26% (95% CI: 15-40%) while specificity was 97% (95% CI: 85-99%). Sensitivity of DECT was 82% (95% CI: 68-90%) while specificity was 89% (95% CI: 73-96%). Fifty-five patients underwent joint aspiration. Sensitivity and specificity of radiographs and NCCT with aspiration as a reference (n = 55) were not much different from that of CGS. However, DECT showed a higher sensitivity of 100% (95% CI: 86-100%) and a lower specificity of 48% (95%CI: 28-68%) with aspiration alone.

CONCLUSIONS

Dual energy computed tomography had higher sensitivity compared to conventional imaging with CGS as a reference; however, its specificity dropped with aspiration as a reference. It may be a useful adjunct for the diagnosis of gout, especially in the acute and inter-critical stage.

Gouty arthropathy: Review of clinico-pathologic and imaging features

Gout is a common inflammatory arthropathy in adults, with the prevalence increasing in males of older age. It occurs when monosodium urate (MSU) crystals are deposited in joints and connective tissue causing inflammation. The gold standard for the diagnosis of gout is the demonstration of negatively birefringent, needle-shaped MSU crystals through synovial fluid aspiration. However, this is an invasive technique and may not always be conclusive or feasible. Imaging techniques have been developed to aid in diagnosis of gout non-invasively. Radiography has a low utility in the early diagnosis of gout and demonstrates erosions in late stages. Ultrasound (US) has a high overall sensitivity in diagnosing gout with the 'double contour' sign having a high specificity. Magnetic resonance imaging is good at detecting tophi, bone marrow oedema and erosions, but has a limited role in diagnosis because of its high cost and limited availability. Conventional computed tomography (CT) has no role in the routine diagnosis of gout before development of erosions and tophi. A newer technology, dual-energy CT (DECT) has been shown to be able to detect MSU crystals burden with high accuracy. It has a higher specificity and lower sensitivity that US in gout diagnosis. However, because of radiation exposure and cost, it has a better utility in diagnosing clinically suspected gout complicated by other concurrent rheumatologic conditions or if radiography, US and synovial aspiration are inconclusive or not feasible. This paper will review the clinico-pathologic and imaging features of gouty arthropathy.

Raman Spectroscopy Applied to the Noninvasive Detection of Monosodium Urate Crystal Deposits

An off-the-shelf Raman Spectrometer (RS) was used to noninvasively determine the presence of monosodium urate (MSU) crystals on the metatarsophalangeal joint (MTPJ) of a single gout sufferer. The spectrum sourced from the clinically diagnosed gout sufferer was compared to that sourced from an age-matched healthy subject scanned using the same protocol. Minimal signal processing was conducted on both spectra. Peaks characteristic of MSU crystals were evident on the spectrum sourced from the gout sufferer and not on the spectrum from the healthy control.

Gadolinium-enhanced MRI features of acute gouty arthritis on top of chronic gouty involvement in different joints

The aims of the current study are to describe gadolinium-enhanced MRI features of an acute flare of established gouty arthritis in different joints and to examine a possible association between serum uric acid and MRI signs indicative of ongoing inflammation and/or structural joint damage as well as association with disease characteristics and laboratory findings. Twenty-seven male patients with established chronic gout agreed to participate, mean age 47.6 years, and mean disease duration in months 43.2 (±31.8). For all patients, detailed demographic, disease characteristics, and laboratory findings were obtained and correlated with MRI findings. In 27 patients with established gout, a total of 50 MRI studies were performed of the following joints: feet joints (n = 23), ankles (n = 18), knees (n = 5), and hand and wrist joints (n = 4). MRI revealed capsular thickening in 19 patients, bone marrow edema (BME) in 15, soft tissue edema (STE) in 20, joint effusion in 21, bone erosions in 17, cartilaginous erosions in 4, and tenosynovitis in 9 cases. In 17 cases, tophaceous lesions were found. Post contrast MRI showed synovial thickening in seven cases. Positive correlations were observed between serum uric acid levels and the following MRI findings: capsular thickening (r = 0.552, p = 0.003), BME (r = 0.668, p ≤ 0.0001), STE (r = 0.559, p = 0.002), and tenosynovitis (r = 0.513, p = 0.006). Using MRI in chronic gout, important features can be detected like BME, minute cartilaginous erosions, and hypertrophic synovial inflammation in post contrast MR images. Serum uric acid (SUA) was positively correlated with capsular thickening, BME, STE, and tenosynovitis.

Imaging as an Outcome Measure in Gout Studies: Report from the OMERACT Gout Working Group

OBJECTIVE

The gout working group at the Outcome Measures in Rheumatology (OMERACT) 12 meeting in 2014 aimed to determine which imaging modalities show the most promise for use as measurement instruments for outcomes in studies of people with chronic gout and to identify the key foci for future research about the performance of these imaging techniques with respect to the OMERACT filter 2.0.

METHODS

During the gout session, a systematic literature review of the data addressing imaging modalities including plain radiography (XR), conventional computed tomography (CT), dual-energy computed tomography (DECT), magnetic resonance imaging (MRI), and ultrasound (US) and the fulfillment of the OMERACT filter 2.0 was presented.

RESULTS

The working group identified 3 relevant domains for imaging in gout studies: urate deposition (tophus burden), joint inflammation, and structural joint damage.

CONCLUSION

The working group prioritized gaps in the data and identified a research agenda.

Imaging in gout: A review of the recent developments

Gout is a common inflammatory arthritis and is caused by accumulation of monosodium urate crystals in joints and soft tissues. Apart from joint damage, untreated gout is associated with cardiovascular and renal morbidity. Gout, whilst in principle considered to be well understood and simple to treat, often presents diagnostic and management challenges, with evidence to suggest that it is often inadequately treated and poor compliance is a major issue. Imaging tools can aid clinicians in establishing the correct diagnosis, when histological crystal diagnosis is unable to be established, and also assess the burden of inflammatory and structural disease. Imaging can also be used to monitor treatment response. The imaging techniques that currently have a role in the imaging of gout include conventional radiography, ultrasound, computed tomography, dual energy computed tomography, magnetic resonance imaging and nuclear medicine. Despite the lack of major technological advances in imaging of gout in recent years, scientific studies of existing imaging modalities have improved our understanding of the disease, and how to best utilize imaging techniques in the clinical setting.

Development of a patient-reported outcome measure of tophus burden: the Tophus Impact Questionnaire (TIQ-20)

Background

Tophus burden is currently measured using physical examination and imaging methods. The aim of this study was to develop a patient-reported outcome (PRO) tool to assess tophus burden in people with gout.

Methods

The responses from interviews with 25 people with tophaceous gout were used to generate items for a preliminary PRO tool. Following cognitive testing of each item, a preliminary 34-item questionnaire was administered to 103 people with tophaceous gout. Rasch analysis generated a 20-item Tophus Impact Questionnaire (TIQ-20). Test-retest reproducibility and construct validity of the TIQ-20 were assessed.

Results

The TIQ-20 responses fit the Rasch model and demonstrated unidimensionality, adequate precision, absence of differential item functioning and adequate person separation index. The TIQ-20 included items related to pain, activity limitation, footwear modification, participation, psychological impact and healthcare use due to tophi. In the 103 patients with tophaceous gout, floor effects were observed in 4.9% and ceiling effects in 1%. The TIQ-20 test-retest intraclass correlation coefficient was 0.76 (95% CI 0.61 to 0.85). All predicted correlations for construct validity testing were observed, including weak correlation with serum urate concentrations (r<0.30), moderate correlation with subcutaneous tophus count and dual energy CT urate volume (r=0.30–0.50), and stronger correlation with Health Assessment Questionnaire scores (r>0.50).

Conclusions

We have developed a tophus-specific PRO in patients with tophaceous gout. The TIQ-20 demonstrates acceptable psychometric properties. Initial results show internal, face and construct validity, reproducibility and feasibility. Further research is required to determine responsiveness to change.

Applications of dual-energy CT in emergency radiology

OBJECTIVE

Recent technologic advances in MDCT have led to the introduction of dual-energy CT (DECT). The basic principle of DECT is to acquire images at two different energy levels simultaneously and to use the attenuation differences at these different energy levels for deriving additional information, such as virtual monochromatic images, artifact suppression, and material composition of various tissues.

CONCLUSION

A variety of image reconstruction and postprocessing techniques are available for better demonstration and characterization of pathologic abnormalities. DECT can provide both anatomic and functional information of different organ systems. This article focuses on the main applications of DECT in emergency radiology.

Features of urate deposition in patients with gouty arthritis of the foot using dual-energy computed tomography

OBJECTIVES

To investigate features of urate deposition in gout and the association between these features and attacks of gouty arthritis using dual-energy computed tomography (CT).

METHODS

Dual-energy CT scans of both feet were performed in 80 consecutive patients with gout and 22 with asymptomatic hyperuricemia.

RESULTS

Overall, 333 areas of urate deposition were found in patients with gout. The most commonly affected sites were the first metatarsophalangeal joint (MPJ; 57/333), the distal area of the first toe (59/333) and the calcaneal bone (61/333). For episodes of the first MPJ arthritis, urate deposits in the flexor pollicis longus muscle tendon (P = 0.02), as well as solitary and punctate depositions (P = 0.03 and 0.01, respectively) were positively related to the acute attacks. For episodes of arthritis around the ankle, deposits in the area, including the talus and inferior tibia, were associated with attacks of arthritis at the ankle (P = 0.02); additionally, deposits in the flexor tendon adjacent to the inferior tibia (P < 0.01) and a punctiform conformation were significantly associated with attacks of arthritis (P = 0.02). Logistic regression analysis showed that deposits around the first MPJ (OR = 3.38, 95% CI: 1.32, 8.17) or around the talus and inferior tibia (OR = 2.83, 95% CI: 1.11, 7.15) would increase the risk of an attack of arthritis.

CONCLUSIONS

Dual-energy CT imaging can be used to detect and analyze the features of urate deposition in patients with gout. Specific features of the deposits appeared to be associated with acute attacks of gouty arthritis.

Tophus burden reduction with pegloticase: results from phase 3 randomized trials and open-label extension in patients with chronic gout refractory to conventional therapy

INTRODUCTION

Two replicate randomized, placebo-controlled six-month trials (RCTs) and an open-label treatment extension (OLE) comprised the pegloticase development program in patients with gout refractory to conventional therapy. In the RCTs, approximately 40% of patients treated with the approved dose saw complete response (CR) of at least one tophus. Here we describe the temporal course of tophus resolution, total tophus burden in patients with multiple tophi, tophus size at baseline, and the relationship between tophus response and urate-lowering efficacy.

METHODS

Baseline subcutaneous tophi were analyzed quantitatively using computer-assisted digital images in patients receiving pegloticase (8 mg biweekly or monthly) or placebo in the RCTs, and pegloticase in the OLE. Tophus response, a secondary endpoint in the trials, was evaluated two ways. Overall tophus CR was the proportion of patients achieving a best response of CR (without any new/enlarging tophi) and target tophus complete response (TT-CR) was the proportion of all tophi with CR.

RESULTS

Among 212 patients randomized in the RCTs, 155 (73%) had ≥ 1 tophus and 547 visible tophi were recorded at baseline. Overall tophus CR was recorded in 45% of patients in the biweekly group (P = 0.002 versus placebo), 26% in the monthly group, and 8% in the placebo group after six months of RCT therapy. TT-CR rates at six months were 28%, 19%, and 2% of tophi, respectively. Patients meeting the primary endpoint of sustained urate-lowering response to therapy (responders) were more likely than nonresponders to have an overall tophus CR at six months (54% vs 20%, respectively and 8% with placebo).

CONCLUSIONS

Pegloticase reduced tophus burden in patients with refractory tophaceous gout, especially those achieving sustained urate-lowering. Complete resolution of tophi occurred in some patients by 13 weeks and in others with longer-term therapy.

TRIAL REGISTRATIONS

NCT00325195, NCT01356498.

Imaging of gout: an overview

The diverse clinical states and sites of pathology in gout provide challenges when considering the features apparent on imaging. Ideally, an imaging modality should capture all aspects of disease including monosodium urate crystal deposition, acute inflammation, tophus, tissue remodelling and complications of disease. The modalities used in gout include conventional radiography, ultrasonography, magnetic resonance imaging, computed tomography and dual-energy computed tomography. This review discusses the role of each of these imaging modalities in gout, focussing on the imaging characteristics, role in gout diagnosis and role for disease monitoring. Ultrasonography and dual-energy computed tomography are particularly promising methods for both non-invasive diagnosis and monitoring of disease. The observation that ultrasonographic appearances of monosodium urate crystal deposition can be observed in patients with hyperuricaemia but no other clinical features of gout raises important questions about disease definitions.

Dual-energy CT: a promising new technique for assessment of the musculoskeletal system

OBJECTIVE

Dual-energy CT (DECT) characterizes the chemical composition of material according to its differential x-ray attenuation at two different energy levels. Applications of DECT in musculoskeletal imaging include imaging of bone marrow edema, tendons, and ligaments and the use of monoenergetic techniques to minimize metal prosthesis beam-attenuating artifacts.

CONCLUSION

The most validated application of DECT is undoubtedly its noninvasive and highly specific ability for confirming the presence of monosodium urate deposits in the assessment of gout.

Clinical utility of dual-energy CT for evaluation of tophaceous gout

Although diagnosing gout generally is straightforward, atypical disease may present a challenge if it is associated with unusual symptoms or sites, discordant serum urate level, or mimics of gout. Dual-energy computed tomography (CT) may be used to differentiate urate crystals from calcium by using specific attenuation characteristics, which may help diagnose gout. In patients with known tophaceous gout, dual-energy CT may be used for serial volumetric quantification of subclinical tophi to evaluate response to treatment. Given the utility of dual-energy CT in challenging cases and its ability to provide an objective outcomes measure in patients with tophaceous gout, dual-energy CT promises to be a unique and clinically relevant modality in the diagnosis and management of gout.

Tophus measurement as an outcome measure for clinical trials of chronic gout: progress and research priorities

Despite the recognition that tophus regression is an important outcome measure in clinical trials of chronic gout, there is no agreed upon method of tophus measurement. A number of methods have been used in clinical trials of chronic gout, from simple physical measurement techniques to more complex advanced imaging methods. This article summarizes methods of tophus measurement and discusses their properties. Physical measurement using Vernier calipers meets most aspects of the Outcome Measures in Rheumatology (OMERACT) filter. Rigorous testing of the complex methods, particularly with respect to reliability and sensitivity to change, is needed to determine the appropriate use of these methods. Further information is also required regarding which method of physical measurement is best for use in future clinical trials. The need to develop and test a patient-reported outcome measure of tophus burden is also highlighted.

Imaging in gout--what can we learn from MRI, CT, DECT and US?

There are many exciting new applications for advanced imaging in gout. These modalities employ multiplanar imaging and allow computerized three-dimensional rendering of bone and joints (including tophi) and have the advantage of electronic data storage for later retrieval. High-resolution computed tomography has been particularly helpful in exploring the pathology of gout by investigating the relationship between bone erosions and tophi. Magnetic resonance imaging and ultrasonography can image the inflammatory nature of gouty arthropathy, revealing synovial and soft tissue inflammation, and can provide information about the composition and vascularity of tophi. Dual-energy computerized tomography is a new modality that is able to identify tophi by their chemical composition and reveal even small occult tophaceous deposits. All modalities are being investigated for their potential roles in diagnosis and could have important clinical applications in the patient for whom aspiration of monosodium urate crystals from the joint is not possible. Imaging can also provide outcome measures, such as change in tophus volume, for monitoring the response to urate-lowering therapy and this is an important application in the clinical trial setting.

Magnetic Resonance Imaging Bone Edema Is Not a Major Feature of Gout Unless There Is Concomitant Osteomyelitis: 10-year Findings from a High-prevalence Population

Objective.

Magnetic resonance imaging (MRI) is commonly used in autoimmune inflammatory arthritis to define disease activity and damage, but its role in gout remains unclear. The aim of our study was to identify and describe the MRI features of gout.

Methods.

Over a 10-year period we identified patients with gout who underwent MRI scanning of the hands or feet. Scans were reviewed for erosions, synovitis, tenosynovitis, tendinosis, bone edema, and tophi by a musculoskeletal radiologist and 2 rheumatologists in a blinded manner. MRI features in patients with uncomplicated gout were compared with features where concomitant osteomyelitis was diagnosed.

Results.

A total of 47 patients with gout (51 scans) were included: 33 (70%) had uncomplicated gout and 14 (30%) had gout complicated by osteomyelitis. MRI features included tophi in 36 scans (71%), erosions in 35 (69%), bone edema in 27 (53%), synovitis in 15 (29%), tenosynovitis in 8 (16%), and tendinosis in 2 (4%). Uncomplicated gout and gout plus osteomyelitis did not differ for most MRI features. However, “severe bone marrow edema” was much more common in gout plus osteomyelitis, occurring in 14/15 scans (93%) compared with 3/36 scans (8%) in uncomplicated gout (OR 154.0, 95% CI 14.7–1612, p < 0.0001). Sensitivity and specificity of “severe bone edema” for concomitant osteomyelitis were 0.93 (95% CI 0.68–0.99) and 0.92 (95% CI 0.78–0.98), respectively.

Conclusion.

MRI reveals that gout affects the joints, bones, and tendons. Bone edema in patients with chronic tophaceous gout is frequently mild and this contrasts with the “severe bone edema” observed in patients with concomitant osteomyelitis.

Tophaceous gout of the knee: revisiting MRI patterns in 30 patients

OBJECTIVE

To evaluate the locations and associated erosions of tophaceous gout in the knee and to reevaluate its characteristic magnetic resonance imaging features.

MATERIALS AND METHODS

We performed a retrospective review of the magnetic resonance (MR) images of the knees of 30 patients with histopathologically confirmed gouty tophi. Each tophaceous lesion was evaluated for location, morphology, signal intensity, and associated bone erosion or intraosseous involvement.

RESULTS

The tophaceous masses were commonly located on the medial aspect of the infrapatellar fat pad and anterior joint recess (n = 28, 87%), the space adjacent to the lateral rim of the lateral femoral condyle (n = 25, 78%), and the intercondylar fossae (n = 22, 69%). All tophaceous lesions showed similar signal characteristics (low-intermediate signal intensities on T1-weighted images, with heterogeneous signal intensities on T2-weighted images), and 3 morphologic patterns were observed: amorphous masses (n = 27), linear crystalline-like deposits (n = 6), and cystic lesions of the bursae around the knee (n = 3). Associated bone erosions occurred in the lateral rim of the lateral femoral condyle (n = 8), the roof of the intercondylar notch (n = 7), the tibial eminence (n = 5), and the medial and lateral rim of the tibial plateau (n = 3). Intraosseous tophi were seen in the tibial plateau (n = 3) and patella (n = 1).

CONCLUSION

Knowledge of the common locations and associated erosions of tophaceous gout and its characteristic MR appearance may facilitate its correct diagnosis with magnetic resonance imaging, particularly in patients with no clinical symptom or only an isolated lesion on MR images.

Progress in Measurement Instruments for Acute and Chronic Gout Studies

Consensus exercises have identified and prioritized domains of measurement for studies in acute and chronic gout. In parallel, the technical properties of instruments for measurement in many of these domains have been assessed, with the main objective to consider the instruments in the context of the OMERACT filter of truth, discrimination, and feasibility. These data were presented and discussed at OMERACT 9 in the gout workshop, in breakout groups, and at informal meetings of the gout group. In acute gout, instruments for domains of pain, joint swelling, joint tenderness, and patient and physician global assessment have been assessed. In chronic gout, some validation exercises have been performed in instruments for domains serum urate, tophus measurement, health-related quality of life (HRQOL). In voting at OMERACT 9, the Medical Outcomes Study Short-Form 36 was endorsed as a valid instrument for measurement of HRQOL. Methods of tophus measurement were considered to have met some criteria of the OMERACT filter, but these require further work, particularly regarding sensitivity to change over shorter time periods. Priorities for future research include measurement of joint inflammation in acute gout and disability in acute and chronic gout.

Imaging of gout: findings and utility

Imaging is a helpful tool for clinicians to evaluate diseases that induce chronic joint inflammation. Chronic gout is associated with changes in joint structures that may be evaluated with diverse imaging techniques. Plain radiographs show typical changes only in advanced chronic gout. Computed tomography may best evaluate bone changes, whereas magnetic resonance imaging is suitable to evaluate soft tissues, synovial membrane thickness, and inflammatory changes. Ultrasonography is a tool that may be used in the clinical setting, allowing evaluation of cartilage, soft tissues, urate crystal deposition, and synovial membrane inflammation. Also ultrasound-guided puncture may be useful for obtaining samples for crystal observation. Any of these techniques deserve some consideration for feasibility and implementation both in clinical practice and as outcome measures for clinical trials. In clinical practice they may be considered mainly for evaluating the presence and extent of crystal deposition, and structural changes that may impair function or functional outcomes, and also to monitor the response to urate-lowering therapy.

Imaging modalities and monitoring measures of gout

PURPOSE OF REVIEW

Imaging modalities for gout have been mostly restrained to radiographs. Ultrasonography, computed tomography and magnetic resonance imaging are emerging techniques that could be used for diagnosis, evaluation, and monitoring acute and chronic gout.

RECENT FINDINGS

Diagnosis of gout is based on urate crystal observation with microscopy. Recently, crystal deposition in the hyaline cartilage has been described to be different in gout from that of calcium pyrophosphate, but validation of the findings is pending. Severity of gout with simple radiographs may not disclose periarticular or intra-articular urate deposition. Ultrasonography, computed tomography and magnetic resonance imaging may improve the evaluation of tophi not apparent in clinical examination or simple radiographs. Monitoring urate deposition may be accomplished with imaging techniques. This would be of outstanding interest for clinical trials, but also for evaluating clinical response to urate-lowering therapy. Although preliminary results evaluating for validity and reliability have been very recently reported for magnetic resonance imaging, computed tomography and ultrasonography, sensitivity to change studies are still pending. Also, monitoring of chronic inflammation with imaging techniques, such as power-Doppler, deserve further studies.

SUMMARY

Evidence exists regarding the usefulness of imaging techniques for diagnosis, evaluation of severity, and monitoring of gout, but further investigation is needed.

Computed tomography measurement of tophus volume: Comparison with physical measurement

OBJECTIVE

Computed tomography (CT) has high accuracy for tophus detection. This study assessed reliability of CT measurement of tophus volume and compared reproducibility of CT with physical measurement of tophus size.

METHODS

Forty-seven hand tophi were analyzed in 20 patients with gout. The longest tophus diameter was recorded by 2 independent observers. All patients proceeded to CT scanning of the hands on a Philips Brilliance scanner (0.8-mm slices). Two independent observers measured tophus volume using the Surface Shaded Display 3-dimensional function on the Philips CT workstation. Five patients underwent repeat physical and CT assessments within 1 week (18 observations). Inter- and intraobserver reproducibility were analyzed by limits of agreement and coefficients of variation.

RESULTS

Of the 47 lesions identified as tophi on physical examination, 42 (89%) were also identified on CT. The mean (95% confidence interval [95% CI]) difference between observers for physical measurement was 0.45 mm (-4.07, 4.96) and for CT was 65.2 mm(3) (-293.0, 423.3). The mean (95% CI) difference between visits for physical measurement was -0.72 mm (-5.47, 4.03) and for CT was -13.1 mm(3) (-112.5, 86.3). There was no difference between coefficients of variation for inter- and intraobserver reproducibility for the 2 measurement techniques. For tophi identified by physical and CT assessment, there was good correlation between measurements (r = 0.91, P < 0.0001).

CONCLUSION

CT assessment of tophus volume is reliable and reproducible. However, physical measurement correlates well with CT and has equivalent reproducibility. These data support the use of physical measurement as a simple and reliable method to assess tophus size.