Background/Purpose: Differentiation of gout and calcium pyrophosphate deposition disease (CPPD) is sometimes difficult as patients often present with a similar clinical picture. Arthrocentesis and subsequent polarization microscopy (PM) remains the gold standard but novel diagnostic approaches such as non-invasive dual energy computed tomography (DECT) have recently been validated for gout. Currently, limited data is available on DECT in patients with CPPD. Our objective was to analyse the diagnostic impact of DECT in gout and CPPD when compared to the gold standard of PM. We further compared the results of PM to ultrasound (US), conventional radiographs (CR), and suspected clinical diagnosis (SCD). Additionally, 12 laboratory parameters were analysed.

Methods: Thirty patients with suspected gout (n = 22) or CPPD (n = 8) were included. Two independent readers assessed colour coded, as well as 80 and 120 kV DECT images for signs of monosodium urate (MSU) crystals or CPP deposition. US, CR, and the SCD were also compared to PM results. US examinations were performed by certified musculoskeletal ultrasound specialists. The association of up to 12 laboratory parameters such as uric acid, thyroid stimulating hormone, and C-reactive protein (CRP) with the PM results was analysed.

Results: Sensitivity of DECT for gout was 59.1% (95% CI 0.36-0.79) with a specificity of 100% (95% CI 0.63-1.00). Concerning CPPD, the sensitivity and specificity of DECT was 37.5% (95% CI 0.09-0.76) and 81.8% (95% CI 0.60-0.95) respectively. US had the highest sensitivity of 90.9% (95% CI 0.71-0.99) with a specificity of 75% (95% CI 0.35-0.97) for gout, while the sensitivity and specificity for CPPD were 87.5% (95% CI 0.47-1.0) and 90.1% (95% CI 0.71-0.99) respectively. The SCD had the second highest sensitivity for gout at 81.8% (95% CI 0.60-0.95) with a comparable sensitivity of 75% (95% CI 0.35-0.97) for CPPD. Uric acid levels were elevated in 26% of gout patients and 25% of CPPD patients. While elevated CRP levels were observed in 60% of gout patients and in 88% of CPPD patients. None of the 12 laboratory parameters were found to be significantly linked to either disease.

Conclusion: DECT is a non-invasive imaging tool for gout but might have a lower sensitivity than published by previous studies (59.1% vs 90%¹). DECT sensitivity for CPPD was 37.5% (95% CI 0.09-0.76) in a sample group of eight patients. Both US and the SCD had higher sensitivities than DECT for gout and CPPD. Further studies with larger patient cohorts are needed in order to determine the diagnostic utility of DECT in CPPD.

Table 1: Sensitivities and specificities of examinations in gout and calcium pyrophosphate deposition disease (95% CI in brackets).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-role-of-dual-energy-computed-tomography-dect-in-the-differentiation-of-gout-and-calcium-pyrophosphate-deposition-disease/