An investigation of the independent risk factors that differentiate gout from pseudogout in patients with crystal-induced acute arthritis: a cross-sectional study

Objectives: To identify independent risk factors that differentiate gout from pseudogout in patients that present with crystal-induced acute arthritis. Methods: This cross-sectional study was conducted at Siriraj Hospital (Bangkok, Thailand) during the 25 May 2014–28 November 2014 study period. Patients who presented with crystal-induced acute arthritis were eligible for inclusion. Diagnosis of gout or pseudogout was made by microscopic visualization and analysis of crystals in synovial fluid. Patients with other causes of acute arthritis were excluded. Patients diagnosed with gout were compared with patients diagnosed with pseudogout and factors with a p value less than 0.05 were included in logistic regression analysis. Results: A total of 103 patients were included. Gout and pseudogout were established in 59 (56.7%) and 44 (42.3%) patients, respectively. Gout patients were younger than pseudogout patients (66.9 ± 14.5 vs. 78.9 ± 12.0 years; p = 0.0001); had higher BMI (22.9 ± 2.5 vs. 21.0 ± 2.5 kg/m²; p = 0.001); had history of recurrent arthritis (91.5 vs. 9.1%; p = 0.001); had higher prevalence of below-knee arthritis (66.1 vs. 31.8%; p = 0.001); had less periarticular soft tissue swelling (57.6 vs. 81.8%; p = 0.01); and had hyperuricemia (8.0 ± 2.5 vs. 5.6 ± 2.7; p = 0.001). In adjusted multivariate analysis, hyperuricemia during acute arthritis/gouty attack characterized gout (OR 2.08, 95% CI 1.2–3.6), while monoarticular attack (OR 4.12, 95% CI 1.3–13.0) and periarticular soft tissue swelling (OR 4.03, 95% CI 1.1–14.9) were indications for pseudogout. Conclusions: The independent risk factors were found to differentiate gout from pseudogout: Gout: hyperuricemia during gouty attack; Pseudogout: monoarticular attack and periarticular soft tissue swelling.