Comparison between dual-energy computed tomography and ultrasound in the diagnosis of gout
Authors: Khanduri Sachin , Singh Vishwesh , Pathak Vaibhav , Bansal Tanya , Panwar Monika , Dhingra Vibhor , Khan Salma , Jamal Hamza 
Published: January 2024

Objectives:
Gout is one of the most common inflammatory arthritic conditions that arise due to the super saturation of urate levels in body tissues, resulting in the formation of monosodium urate (MSU) crystals that get deposited in and around the joints. Clinical diagnosis of gout is generally made based on signs and symptoms. The biochemical diagnosis is based on the levels of serum uric acid. However, hyperuricemia is a weak marker for gout diagnosis. The gold standard for diagnosing gout is the identification of MSU crystals in the synovial fluid by Polaroid microscopy. However, it is an invasive procedure that could lead to complications such as joint effusion and intra-articular hemorrhage. Imaging offers a non-invasive method for the diagnosis of gout. Ultrasound (USG) has emerged as a useful measure for detecting joint effusion and synovitis, studying cartilage, describing early bone erosions, and evaluating tendons and crystal deposition. Dual-energy computed tomography (DECT) is a useful non-invasive technique that helps visualize MSU crystals, along with other soft tissue changes and erosive pathologies, at high resolution, much earlier than conventional radiography could do.

Material and Methods:
Clinically suspected or diagnosed gout patients in the age group of 20–75 years of both genders attending outpatient services were selected for the study. All the patients fulfilling the inclusion criteria of clinical suspicion of gout or already proven cases of gout were clinically examined, and body mass index, presenting complaints, symptomatic joints, past medical history, family history, and personal habits were noted. The diagnosis of gout was confirmed using the 2015 American college of rheumatology/European league against rheumatism (ACR/EULAR) classification criteria: A cut-off score >8 was considered diagnostic. Thereafter, all the patients underwent ultrasonographic and computed tomography evaluations. All the patient’s assessments were made at nine locations bilaterally – shoulder, neck, wrist, metacarpal, metatarsophalangeal, ankle, hip, knee, and elbow to check for multiple joint involvements. All the DECT images were post-processed, allowing analysis of images using the three material decomposition methods. On reconstructed DECT images, green color-coded MSU crystals were considered suggestive of gout.

Results:
The present study reported a higher detection of gout on DECT (97.1%) as compared to the USG (88.2%). Similarly, several studies reported a higher detection rate of MSU crystal deposition by DECT as compared to the detection of the double-contour sign by USG. This study reported sensitivity, specificity, positive predictive, and negative predictive value (PPV and NPV) of USG as 91%, 92%, 95%, and 85%, respectively. In contrast, DECT’s sensitivity, specificity, PPV, and NPVs were 96%, 100%, 100%, and 92%, respectively. DECT showed to have a high sensitivity as well as specificity.

Conclusion:
The study showed that DECT is more sensitive and had a better PPV and accuracy than USG in the diagnosis of gout. Keeping in view the high efficacy of DECT in diagnosing gouty joints, it is a strong candidate to emerge as a non-invasive imaging modality of choice for diagnosing gout.