The reasons for such patterns of MSU crystal deposition are currently unknown, and these observations provide a platform for new studies to examine the mechanisms of MSU crystal formation in vivo. DECT has also demonstrated a close relationship between structural joint damage and MSU crystal deposition; implicating interactions between crystals and structures within the joint in the development of bone erosion, new bone formation and cartilage damage in gout (see Figure 3).10
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Explore This IssueJune 2014
Despite the utility of DECT, there are some disadvantages and pitfalls that require consideration. First, this technology requires specialized hardware and software, which are costly and not universally available. It requires the use of radiation; the estimated dose is 0.5 mSv per region scanned. Although peripheral regions are usually assessed, frequent repeated measurement is not feasible due to the accumulating risks of medical radiation dosing.
Artifact can distort images at certain sites, such as within thick heel pads and toenails (see Figure 4). Volume assessments should ideally exclude such potential areas of artifact. Technical issues, such as changes in the ratio settings, may substantially alter sensitivity and specificity. The limits of detection of DECT may be lower than ultrasonography, and in particular low concentrations of MSU crystals within joint fluid may not be detected by this imaging method.5,7
Despite these potential limitations, DECT represents an important advance in the clinical management and understanding of gout. Perhaps the most valuable contribution has been the ability to visualize the extent of MSU crystal deposition on DECT scans, even during periods when the patient is not experiencing an acute gout flare. These images emphasize the fundamental concept regarding gout as a chronic disease of MSU crystal deposition. This key concept justifies the central strategy for the effective management of gout, namely the lowering of the serum urate as a way to dissolve crystals. In addition, the pictorial images of the disease provide a clear explanation for prescribing urate-lowering drugs. Thus DECT may serve as a powerful tool for patient understanding and for improving adherence to long-term hypouricemic therapy.
Nicola Dalbeth, MBChB, MD, FRACP, is a rheumatologist and associate professor in the Bone and Joint Research Group, Department of Medicine, University of Auckland, Auckland, New Zealand.
- Johnson TR, Weckbach S, Kellner H, et al. Clinical image: Dual-energy computed tomographic molecular imaging of gout. Arthritis Rheum. 2007;56(8):2809.
- Choi HK, Al-Arfaj AM, Eftekhari A, et al. Dual energy computed tomography in tophaceous gout. Ann Rheum Dis. 2009;68(10):1609–1612.
- Glazebrook KN, Guimaraes LS, Murthy NS, et al. Identification of intraarticular and periarticular uric acid crystals with dual-energy CT: Initial evaluation. Radiology. 2011;261(2):516–524.
- Choi HK, Burns LC, Shojania K, et al. Dual energy CT in gout: A prospective validation study. Ann Rheum Dis. 2012;71(9):1466–1471.
- Gruber M, Bodner G, Rath E, et al. Dual-energy computed tomography compared with ultrasound in the diagnosis of gout. Rheumatology (Oxford). 2014;53(1):173–179.
- Manger B, Lell M, Wacker J, et al Detection of periarticular urate deposits with dual energy CT in patients with acute gouty arthritis. Ann Rheum Dis. 2012;71(3):470–472.
- Melzer R, Pauli C, Treumann T, et al. Gout tophus detection—A comparison of dual-energy CT (DECT) and histology. Semin Arthritis Rheum. 2013;Epub ahead of print.
- Dalbeth N, Aati O, Gao A, et al. Assessment of tophus size: A comparison between physical measurement methods and dual-energy computed tomography scanning. J Clin Rheumatol. 2012;18(1):23–27.
- Dalbeth N, Kalluru R, Aati O, et al. Tendon involvement in the feet of patients with gout: A dual-energy CT study. Ann Rheum Dis. 2013;72(9):1545–1548.
- Dalbeth N, Aati O, Kalluru R, et al. Relationship between structural joint damage and urate deposition in gout: A plain radiography and dual-energy CT study. Ann Rheum Dis. 2014;Epub ahead of print.