SAT0539 DUAL ENERGY CT FINDINGS IN GOUT WITH RAPID KILOVOLTAGE-SWITCHING SOURCE WITH GEMSTONE SPECTRAL IMAGING
Authors: Elin Svensson, Ylva Aurell, Lennart T.H. Jacobsson, Anton Landgren, Valgerdur Sigurdardottir, Mats Dehlin
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> The gold standard for diagnosis of gout is the demonstration of monosodium urate(MSU) crystals in the synovial fluid or in tophi. However, joint aspiration is seldom performed and most patients do not have visible tophi. Dual energy CT(DECT) has been shown capable of detecting MSU crystals with high precision in many studies but the vast majority of these studies were performed using CT scanners with two X-ray tubes(dual source) while the performance of other technical CT solutions are much less investigated. <h3>Objectives</h3> In the present study we wanted to investigate the performance of DECT with rapid kilovoltage-switching source with Gemstone Spectral Imaging(GSI) to identify MSU crystals and validate these results against severity of gout disease. <h3>Methods</h3> Patients with incident/prevalent gout who had been examined with DECT GSI scanning of the feet at Sahlgrenska University Hospital, Sweden between 2015 and 2018 were identified. Their medical records were examined for gout disease characteristics (onset of disease, tophi, erosive disease), comorbidities, medication, body mass index(BMI), serum urate, and renal function. Their DECT GSI images were examined by two radiologists in two consensus readings. Urate deposits in MTP1, MTP 2-5, ankle/midfoot joints and tendons were scored semiquantatively in both feet in the following manner: 0=no deposit, 1=dots, 2=single deposit and 3=more than 1 deposit, thus generating a maximum total score of 24 for both feet and a maximum score of 6 per location) Presence of artefacts in nail and skin as well as beam hardening and noise were also identified. <h3>Results</h3> We identified a total of 55 patients, mean age 58 years (SD=15), with a clinical diagnosis of incident or prevalent gout who all fulfilled the 2015 ACR/EULAR classification criteria for gout. Mean disease duration was 7 years (SD=7). A minority of patients (40%) were on urate lowering treatment(ULT) at time of DECT(table1). The majority of patients had increased urate (&gt;360 μmol/L), irrespective of ULT(table 1). Urate deposits were found in the feet of all patients, most commonly seen in the MTP-joints but also present in ankle/midfoot joints and tendons(table 1). The total urate deposit score was significantly higher in the presence of clinically identified tophi(Wilcoxon Mann-Whitney, p=0.0005) and correlated strongly to disease duration(Spearman corr. coefficient 0.64, p&lt;.0001) while no association or correlation was seen to age, sex, erosive disease, urate levels, BMI, diuretic or ULT use or renal function. The majority of patients displayed nail artefacts while skin artefacts only were seen in 31% (table 1). Beam hardening was only found in one patient and noise was not seen at all(table 1). <h3>Conclusion</h3> The DECT GSI technique performs well in detection of urate deposits and these correlate to clinical gout characteristics in the same manner as previously shown with DECT dual source technique. <h3>Disclosure of Interests</h3> Elin Svensson: None declared, Ylva Aurell: None declared, Lennart T.H. Jacobsson Consultant for: LJ has received lecture and consulting fees from Pfizer, Abbvie, Novartis, Eli-Lily and Janssen, Anton Landgren: None declared, Valgerdur Sigurdardottir: None declared, Mats Dehlin: None declared