Dual energy provides new insight in the distribution of disease of gout

History

A 53 year old patient presented to the rheumatologist with right knee pain that was associated with a locking knee while walking. This patient had a past history of aspiration-proven gout affecting his first metatarsophalangeal joint. No active inflammation and subcutaneous nodules that would be suggestive of tophus. Mild degenerative joint changes were evident, but without limited range of motion. The clinical picture suggested that of an inflammatory arthritis, however, the problem was determining how to diagnose the pathology. There typically are not radiographic findings on X-ray and single energy CT for acute gout. The patient was referred for a Dual Energy CT scan of the patient’s joints.

Diagnosis

After the Spiral Dual Energy scan and post processing the image with the “Kidney Stones” protocol, uric acid deposits were seen along the patient’s PCL and ACL as well as intra-articular tophi. These intra-articular tophi were determined to be the cause of the patient’s pain and “locking” knee. Incidental finding was of uric acid deposits on the patient’s Achilles’ tendon.

Comments

The DSCT (Siemens Definition scanner) system is equipped with two X-ray tubes and two corresponding detectors. These tubes scan at 80 kbp and 140 kbp allowing for material-specific differences in the attenuation of the scanned tissue to be fused into data sets. A 3 material decomposition algorithm (calcium, uric acid, soft tissue) of the data sets loaded in the dual energy viewer present on the Siemens MMWS. Doing so allows for accurate characterization of uric acid (colored in red) separately from soft tissue and calcium (colored in blue). The distribution of gout visualized showed deposition in tendons and ligaments as well as intra-articularly. This unique non-invasive method of visualizing gout can help with diagnosing gout in the acute setting as well as determine the pattern of distribution of disease.

[1] Dual Energy CT scan demonstrating increased attenuation over the posterior cruciate ligament and origin of patellar tendon.	[2] Setting for material differentiation for the Dual Energy CT using the “Kidney Stones” algorithm.
[3] Dual Energy sagittal CT image with “kidney stones” postprocessing demonstrating uric acid deposits on the posterior cruciate liagament and proximal attachment of the patella with resultant erosion of the patella.	[4] VRT coronal image demonstrating uric acid deposits along proximal and distal attachment of the patella and intra-articular tophus deposits along the medial aspect of the knee.
[5] Dual Energy CT Scan processed sagittal image with red color indicating uric acid deposits along distal attachment of Achilles tendon.	[6] Coronal VRT image showing uric acid deposits in patient’s 1st Metatarsophalangeal joints bilaterally as well as in the patient’s R. Achilles tendon.