SAN FRANCISCO — Dual-energy CT scans showed red-colored uric acid deposits in 20 consecutive patients with clinically obvious tophaceous gout but not in 10 control subjects with other nongout joint conditions.
The 100% sensitivity and specificity of dual-energy computed tomography (DECT) scans to identify uric acid deposits could provide a sorely needed accurate imaging tool to aid in the diagnosis of gout and its response to treatment, Dr. Abdullatif M. Alarfaj said at the annual meeting of the American College of Rheumatology.
DECT assesses chemical composition and provides specific color-coded displays to differentiate between uric acid (which shows up as red), calcium (blue), and other renal calculi, previous investigators have shown.
The current proof-of-concept study, in addition to assessing the accuracy of DECT in gout patients, also measured the uric acid burden in peripheral joints and performed a computerized quantification of tophus volume. The volume of uric acid deposits in each anatomic area was measured by automated volume estimation software. The sum of tophus volume in the hands, wrists, elbows, feet, ankles, and knees comprised the total uric acid volume of peripheral joints.
DECT scans identified 440 areas of urate deposition, compared with 111 areas identified on clinical examination, reported Dr. Alarfaj of the University of British Columbia, Vancouver, and his associates. The investigators have no conflicts of interest related to this study.
DECT could be useful in detecting subclinical tophus deposits and the extent of intra- and extra-articular gout, Dr. Alarfaj suggested. Treatment response might be monitored by using DECT to measure both individual tophus volume and total tophus burden.
This relatively new technology also may prove useful in evaluating nodular lesions, diagnosing concurrent gout in patients with other arthropathies, and identifying urate deposits in body areas that are atypical for gout or challenging to assess.
An individual DECT scan can cost about one-sixth of the amount for an MRI, Dr. Alarfaj's senior investigator, Dr. Hyon Choi, said during a question-and-answer session. The DECT hardware equipment is expensive but is used for a variety of purposes, such as imaging coronary artery calcifications and renal calculi, added Dr. Choi, also of the university.
The technology provides dramatic color displays and can be used to create impressive three-dimensional images of uric acid deposits that could aid clinicians in communicating about the disease to patients with gout, he added.
The patients in the gout group of the study had an average 12-year history of the disease and nine painful joints in the previous year. The mean serum uric acid level was 492 micromol/L. The patients had a mean age of 63 years, 15 (75%) were men, and 12 (60%) were white. Comorbid conditions were present in 17 patients (85%).
DECT shows uric acid deposits in red, while calcium in bone looks blue.
A 3-D volume-rendered image of the same patient shows many tophi (red). Images courtesy Dr. Hyon Choi