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This noninvasive modality may be used to investigate joint damage and distinguish between asymptomatic conditions.
Patients with gout and elevated serum uric acid levels, but no symptoms, still displayed ultrasound evidence of urate deposition, tissue inflammation, and bone erosion in their first metatarsophalangeal (MTP) joint on ultrasound when compared with patients who had normal serum uric acid levels.
Patients with elevated uric acid levels, but no symptoms, showed no evidence of tissue inflammation or joint damage on ultrasound, but the frequency of subclinical urate deposition in these patients was similar to that in patients with gout.
Sarah Stewart and colleagues in New Zealand highlighted the importance of distinguishing between gout and isolated hyperuricemia that is asymptomatic.
Disability and pain related to inflammation of the first MTP joint are common in patients with gout. Ultrasound represents a noninvasive and cost-efficient way to confirm features of urate deposition, inflammation, and bone erosion associated with gout but not asymptomatic hyperuricemia.
The authors presented their comparison of ultrasound findings in the first MTP joint of patients with symptomatic gout and patients with asymptomatic hyperuricemia in a recent Arthritis Care & Research article.
In the study, 86 adults were recruited in Auckland, New Zealand; 23 had a diagnosis of gout, 29 did not have gout but had a serum uric acid level ≥ 6.9 mg/dL, and 34 in the control group had serum uric acid levels < 6.9 mg/dL.
High-resolution ultrasound was used to determine the presence of joint effusion, erosion, synovial hypertrophy, and synovitis, as well as tophi presence and magnitude.
• Of the patients with gout, 83% had a history of acute MTP joint arthritis and 26% had clinical evidence of tophi in that joint.
• Patients with gout were more likely to have severe erosions of the MTP joint (odds ratio, 101.8, P<0.001), more severe synovial hypertrophy (OR, 11.73, P=0.002), and more severe synovitis (OR, 47.51, P=0.002) than controls.
• Patients with asymptomatic hyperuricemia were more likely to have severe effusions (OR, 3.08, P=0.046) than controls.
• Patients with gout had significantly larger tophus diameter (P=0.035) and erosion diameter (P<0.001) than controls.
• More severe erosion and synovitis and less severe effusion were independently associated with gout when compared with asymptomatic hyperuricemia (R2=0.65, P<0.001).
Implications for physicians
• Ultrasound is a useful noninvasive modality for investigating joint damage in patients with gout and may help distinguish between patients with asymptomatic hyperuricemia and those with asymptomatic gout.
• Urate deposition, soft tissue inflammation, and bone erosion can be seen on ultrasound and are common in the first MTP joint of patients with gout even when they are asymptomatic.
• Patients who do not have gout but do have asymptomatic hyperuricemia do not have inflamed joints or structural changes on ultrasound, but the rate of subclinical urate deposition is similar to that in patients who have asymptomatic gout.
• The double contour sign (evidence of urate deposition in the joint) seen via ultrasound is significantly more common in patients with gout.
• These results support the concept that gout is a persistent condition, with and without symptoms, characterized by a subclinical immune response to the presence of urate crystals in joints that may lead to symptomatic flare-ups.
Arthritis New Zealand provided financial support for this study.
Sarah Stewart, Nicola Dalbeth, Alain C. Vandal, et al. “Ultrasound Features of the First Metatarsophalangeal Joint in Gout and Asymptomatic Hyperuricemia: Comparison With Normouricemic Individuals.” Arthritis Care Res (Hoboken). 2017;69:875-883. doi: 10.1002/acr.23082. Epub 2017 May 8.