Recent developments in advanced imaging in gout

Abstract

The plain radiographic features of gout are well known; however, the sensitivity of plain radiographs alone for the detection of signs of gout is poor in acute disease. Radiographic abnormalities do not manifest until late in the disease process, after significant joint and soft tissue damage has already occurred. The advent of dual-energy computed tomography (DECT) has enabled the non-invasive diagnosis and quantification of gout by accurately confirming the presence and extent of urate crystals in joints and soft tissues, without the need for painful and often unreliable soft tissue biopsy or joint aspiration. Specific ultrasound findings have been identified and may also be used to aid diagnosis. Both ultrasound and magnetic resonance imaging (MRI) may be used for the measurement of disease extent, monitoring of disease activity or treatment response, although MRI findings are nonspecific. In this article we summarize the imaging findings and diagnostic utility of plain radiographs, ultrasound, DECT, MRI and nuclear medicine studies in the assessment as well as the implications and utility these tools have for measuring disease burden and therapeutic response.

Keywords: crystal arthropathy; diagnostic imaging; dual-energy computed tomography; gout; magnetic resonance imaging; ultrasound.

Figure 1.

Podagra with soft tissue and intra-articular tophi. There is a well-defined ‘punched out’ erosion at the head of the first metatarsal (black arrow) with a paucity of peri-articular osteopenia.

Figure 2.

(a, b). Bilateral hand plain radiographs from the same patient demonstrating extensive high attenuation soft tissue foci representing large tophi. There is relative sparing of the joint spaces and articular surfaces with no osseous erosion or secondary degenerative articular changes. Apparent bilateral middle finger joint space narrowing is projectional. (c). Three-dimensional DECT reconstruction demonstrating extensive urate deposition depicted by soft tissue lesions which, by convention are coloured green (white arrows). Deposits are seen within soft tissue tophus at the dorsum of both wrists, the index and little finger metacarpophalangeal joint of the right hand and the proximal interphalangeal joints of the index and middle fingers of the left hand. (d). Axial noncontrast CT image demonstrating extensive hyper-dense soft tissue tophus overlying the distal ulna (white arrow). CT, computed tomography; DECT, dual-energy computed tomography.

Figure 3.

Ultrasound images of the first metatarsophalangeal joint in a patient presenting with an acute gout attack. Tophus is demonstrated by bright, echogenic crystals interspersed with hypoechoic septa (a) which demonstrate increased Doppler signal (b).

Figure 4.

Ultrasound images of the first metatarsophalangeal joint in a patient presenting with an acute gout attack. The double contour sign is demonstrated by an echogenic line paralleling the subcortical bone plate of the head of the first metatarsal (white arrow).

Figure 5.

Two and three-dimensional DECT reconstructed images of the knee in a patient with gout affecting the extensor mechanism. (a). Red histogram displaying the effective z value of the material within the region of interest displayed on two-dimensional CT (black star). The characteristic urate peak (white arrow) is demonstrated indicating the presence of urate crystals in this region. A second region of interest has been placed in the quadriceps tendon (black arrow) and the associated yellow histogram reveals higher effective z values with no urate peak. (b). Three-dimensional reconstructed images, which urate is displayed within the extensor mechanism and at the lateral joint margin. CT, computed tomography; DECT, dual-energy computed tomography.

Figure 6.

(a). Artefactual urate image appearances at the skin/air interface over the heels and at the head of the 5th metatarsals bilaterally (white arrows). (b). Artefactual urate deposition at the nail beds of the bilateral great toes (white arrows). The location of this apparent urate indicates that it is artefactual and should be distinguished from true soft tissue urate deposition.

Figure 7.

Images of the knee in a patient with extensive tophus within the patella tendon. (a). Sagittal T2-weighted image with fat saturation. (b). Axial T2-weighted image with fat saturation. (c). Sagittal proton density-weighted image. (d). Sagittal noncontrast CT image. Tophus demonstrates heterogeneous signal characteristics however the location and presence of well-defined bone erosion (best seen on CT) are highly suggestive of the diagnosis of gout. CT, computed tomography.