Diagnostic Considerations

The European League Against Rheumatism (EULAR) guidelines state that characteristic imaging features on ultrasound or DECT can confirm gout diagnosis without crystal identification, especially when the double-contour sign or tophi are present 1
The presence of crystal deposition on DECT, double-contour sign on ultrasound, or tophi on ultrasound or DECT can diagnose gout without crystal confirmation, as per the 2023 EULAR guidelines 2
Arthrocentesis may be unsuccessful or technically impossible, and facilities or expertise to analyze joint fluid may be lacking, making imaging a crucial diagnostic tool 1
The lack of access to proper microscopy equipment and trained personnel can hinder crystal identification, highlighting the importance of imaging in diagnosis 3

Imaging Modalities

Ultrasound and DECT are recommended as definitive diagnostic modalities for gout, with key imaging findings including the double-contour sign, tophi, and MSU crystal deposition 4
Conventional radiography and ultrasound are recommended for CPPD diagnosis, while imaging is absolutely necessary for BCPD diagnosis due to the difficulty of BCP crystal analysis 4
Either conventional radiography or ultrasound should be used for BCPD diagnosis, as diagnosis is dependent on imaging rather than crystal identification 5

When clinical suspicion of crystal arthritis is present, arthrocentesis should be attempted if feasible, followed by imaging studies such as ultrasound or DECT for suspected gout, conventional radiography and ultrasound for suspected CPPD, or conventional radiography or ultrasound for suspected BCPD 1
If characteristic imaging features are present, diagnosis can be confirmed without crystal identification, but if imaging is equivocal, repeat arthrocentesis or disease-specific target sites should be considered 4

The detection of MSU crystals has excellent diagnostic value with a sensitivity of 0.84 and a specificity of 1.00 during acute gout attacks, according to the European League Against Rheumatism, making crystal identification virtually pathognomonic for gout when present 6
The likelihood ratio for MSU crystal detection is remarkably high at 566.60, as recommended by the American College of Rheumatology, making it a key diagnostic tool for gout 7

MSU crystals can be identified in both symptomatic and asymptomatic joints, and the American College of Rheumatology recommends routine search for MSU crystals in all synovial fluid samples from undiagnosed inflamed joints, with a strength of recommendation of 90 6, 8
The European League Against Rheumatism suggests that joint aspiration with crystal identification remains the gold standard for diagnosis, though clinical algorithms can achieve sensitivities and specificities greater than 80% when synovial fluid analysis is not feasible 7, 8

The American College of Rheumatology recommends always performing synovial fluid Gram stain and culture when septic arthritis is suspected, even if MSU crystals are identified, as coexistent septic arthritis and gout can occur in the same joint, with a sensitivity of 0.76 and specificity of 0.96 for synovial fluid culture 6, 9