Background/Purpose: Dual energy computed tomography (DECT) is emerging as a diagnostic tool for gout, but its sensitivity has not been established. We assessed the sensitivity of DECT for the detection of monosodium urate (MSU) deposits in both non-tophaceous and tophaceous gout.
Methods: Twenty-one patients with gout (per Wallace criteria) agreed to participate in this study funded by Siemens Medical Solutions and underwent DECT of their hands, wrists, elbows, knees, ankles, and feet. Eleven had non-tophaceous gout confirmed by the demonstration of MSU crystals in a joint aspirate. Ten patients had tophaceous gout (crystal-proven in 7), defined by the presence of palpable tophi (n=5), the presence of erosions of the first metatarsal head on radiograph (n=3), or gross MSU deposits in a surgical specimen (n=2). Scans were performed using a SOMATOM Definition Flash Dual Source CT scanner (Siemens Healthcare) with simultaneous acquisition of images at 80 and 140 kV. Post-processing was performed using Siemens software with predefined standard parameters; the threshold ratio parameter was set at 1.36. Sensitivity was defined as the percentage of gout patients who were correctly identified by DECT.
Results: The 21 patients included 17 men, with a mean age of 61 years (range, 43 – 83). Among the 11 patients with non-tophaceous gout, MSU deposits were only detected by DECT in the joint proven to be affected by aspiration in 2 (sensitivity=18%). However, the MSU deposits were evident in ≥1 joint area evaluated by DECT in 7 patients (overall sensitivity=64%), ≥1 clinically affected joint in 4 (57%) patients and ≥1 clinically unaffected joint in 6 (86%) patients. The number of MSU deposits correlated with the maximum recorded serum urate (r2=0.502, p=.022) but not with gout duration. Among the 10 patients with tophaceous gout, 9 had MSU deposits evident by DECT (sensitivity=90%). In an index case of tophaceous gout (Figure), we were surprised to see tophi evident by clinical examination (panel A), 3D volume rendering (Panel B), and bony erosion (panel C-little finger DIP), that were negative by DECT (panel C-lack of green deposits). This prompted us to evaluate the sensitivity of DECT for individual gouty erosions (defined by the presence of an overhanging edge in a joint not affected by severe joint space loss). In 3 patients with extensive foot involvement, MSU deposits were detected by DECT within or immediately adjacent to 13/26 (50%) erosions.
Conclusion: DECT detected MSU deposits in non-tophaceous gout, with 65% sensitivity on scanning of both upper and lower extremity joints and only 18% on scanning of the crystal-proven joint. The sensitivity was 90% in tophaceous gout, but remained inadequate when evaluated on the basis of individual erosive lesions. The detection of MSU deposits by DECT may relate to their density and this could potentially be improved with an adjustment of algorithm input parameters.