Dual-energy computed tomography has limited sensitivity for non-tophaceous gout: a comparison study with tophaceous gout

Abstract

BackgroundDual-energy computed tomography (DECT) is a new diagnostic tool for gout, but its sensitivity has not been established. Our goal was to assess the sensitivity of DECT for the detection of monosodium urate (MSU) deposits in non-tophaceous and tophaceous gout, both at the level of the patient and that of the individual joint or lesion.MethodsDECT was performed on 11 patients with crystal-proven non-tophaceous gout and 10 with tophaceous gout and included both the upper and lower extremities in 20/21 patients. DECT images were simultaneously acquired at 80 and 140 kV and then processed on a workstation with proprietary software using a two-material decomposition algorithm. MSU deposits were color coded as green by the software and fused onto grey-scale CT images. The number and location of these deposits was tallied independently by two DECT-trained radiologists blinded to the clinical characteristics of the patient. Sensitivity of DECT was defined as the proportion of patients with a confirmed diagnosis of gout which was correctly identified as such by the imaging technique. All patients provided informed consent to participate in this IRB-approved study.ResultsMSU deposits were detected by DECT in ≥1 joint area in 7/11 (64 %) patients with non-tophaceous gout, but were only detected in 3/12 (25 %) joints proven by aspiration to be affected with gout. Inclusion of the upper extremity joints in the scanning protocol did not improve sensitivity. All 10 patients with tophaceous gout had MSU deposits evident by DECT. The sensitivity of DECT for individual gouty erosions was assessed in 3 patients with extensive foot involvement. MSU deposits were detected by DECT within or immediately adjacent to 13/26 (50 %) erosions.ConclusionsA DECT protocol that includes all lower extremity joints has moderate sensitivity in non-tophaceous and high sensitivity in tophaceous gout. However, DECT has lower sensitivity when restricted to individual crystal-proven gouty joints in non-tophaceous disease or individual erosive lesions in tophaceous gout. The detection of MSU deposits by DECT relates to their size and density and the detection parameters of the DECT scanner and adjustment of the latter might improve sensitivity.

Diagnosing Gout with Dual-energy Computed Tomography: Principles, Diagnostic Performance, and Clinical Application

“…In a study of 11 patients with crystal-proven non-tophaceous gout and 10 with tophaceous gout, dual-energy CT detected MSU deposits in one or more joint area in seven (64%) patients with non-tophaceous gout but only in three (25%) of 12 joints confirmed by aspiration, whereas MSU deposits were detected in all 10 patients with tophaceous gout. 9 In addition, dual-energy CT can be used to quantify MSU deposition within tophi, with intra-reader and inter-reader intraclass correlation coefficients of 1.0 (for volume measurement) and bias estimates of 0.01 cm 3 ; reliability of dual-energy CT did not vary with different sites or sizes of tophi. 8 False-negative results can be due to less-dense tophi with lower crystal concentrations, small size of tophi / crystals (<2 mm), or technical parameters.…”

Advanced Imaging in the Diagnosis of Gout and Other Crystal Arthropathies

“…37 Baer et al also showed that MSU deposits are more frequently seen in tophaceous gout (sensitivity 100%) than in non-tophaceous gout (sensitivity 64%). 38 Melzer et al in a case report with histopathologic correlation found that DECT only highlighted dense tophi, corresponding to 15 to 20% volume of urate in the tophus. 39 In their study, less dense tophi, despite considerable size, were missed on the color-coded images using standard DECT thresholds.…”

Top-Ten Tips for Dual-Energy CT in MSK Radiology

“…DECT has moderate sensitivity in non-tophaceous gout and high sensitivity in tophaceous gout. 51 It was noted, however, that DECT had lower sensitivity when restricted to individual crystal-proven gouty joints in non-tophaceous disease or individual erosive lesions in tophaceous gout.…”

“…These images and analyses are often straightforward, but detection of MSU deposits relates to their size and density and optimal scanner parameters. 51 In general, we recommended a 50%-50% overlay.…”