Background: Dual Energy CT Scan (DECT) can detect monosodium urate crystal deposits in multiple tissues. EULAR gout guidelines (Richette, 2020) recognized the value of DECT in making a clinical diagnosis when joint aspiration is difficult. DECT shows crystal deposits in almost 50% of gout patients without tophi (Dalbeth, 2017). Tophi are known to predict all-cause and cardiovascular mortality (Vincent 2017, Perez-Ruiz 2013) and it is plausible that DECT could as well. A prognostic measure should be reliable and valid. DECT validity would be evident for death, disability and distress.

Objectives: This study used a best evidence synthesis approach to synthesize the evidence for DECT as a prognostic measure in gout.

Methods: PUBMED and EMBASE were searched from initiation to December 2019; keywords (Dual Energy Computed Tomography OR DECT, gout, tophaceous gout, chronic gout, monosodium urate crystals OR monosodium urate burden OR tophi OR monosodium urate volume OR flares OR pain OR distress OR death OR disability OR function). Human studies in English were considered. Titles, abstracts and full articles were reviewed. A manual search of secondary sources was conducted. Key gaps identified were considered throughout 2020 when reviewing emerging articles and presentations. Data extraction was conducted by both authors; data presented represents consensus.

Results: Of 344 articles, 81 titles/abstracts met screening inclusion criteria (24%) in the 2019 search; review of the full manuscript led to 41 articles selected (51%). Additionally, 3 key papers and 2 ACR 2020 presentations were identified through 2020. DECT is highly reliable with inter-class correlation coefficients >0.9. DECT has content validity. Dalbeth (2015) showed DECT and X-Rays findings correlated in tophaceous patients, r=0.70, p<0.001. Hand function correlates with DECT burden, with r ² =0.59, p=0.024 (Dalbeth 2007). Dalbeth (2017) showed DECT associated with greater flares at 3 and 12 months (p<0.01) in 152 patients. Pascart (2018) confirmed that subjects with flares had nearly doubled DECT feet volumes (0.9 vs 2.1 cm ³ , p=0.05) versus those not flaring. Dalbeth (2017) showed abnormal DECT scans occurred in 47% of patients with normal uric acid (<6.0 mg/dL) without palpable tophi and in 90% with elevated uric acid and palpable tophi. DECT is very sensitive to change (Araujo 2015) with 95% volume reduction in 152 patients on pegloticase treated up to 12 months. Three studies show DECT is correlated to cardiovascular risk factor prevalence (Pascart 2020, Gamala 2018, Lee 2017). Marty-Ané reported that DECT volume predicts mortality (Marty-Ané ACR 2020). Limited evidence from 3 studies suggests that the minimum important volume for DECT is 1.0 cm ³ at feet and ankles, including Pascart 2020.

Conclusion: DECT imaging is highly reliable, has evidence for content validity and is highly sensitive to change. DECT appears to predict future gout flares, cardiovascular risk factor prevalence and mortality. Minimum important DECT volume approximates 1.0 cm ³ . DECT requires further study but appears to be a relevant outcome for clinical trials and staging gout patients.

Disclosure of Interests: Sally Stauder: None declared, Paul M. Peloso Shareholder of: Horizon Therapeutics plc, Employee of: Horizon Therapeutics plc.