Background/Purpose: The first metatarsophalangeal joint (1MTPJ) is frequently affected in gout. This study aimed to identity ultrasound features of the 1MTPJ in people with gout and people with asymptomatic hyperuricaemia compared with normouricaemic controls.

Methods: Participants with gout (n=23), asymptomatic hyperuricaemia (n=29) and age- and sex-matched normouricaemic control participants (n=34) underwent a grey-scale and power Doppler ultrasound assessment of both 1MTPJs using a Phillips iU22 ultrasound machine with a 10 MHz, 55mm linear array transducer. No participants had clinical evidence of gout flare at the time of scanning. The images were assessed by two blinded independent radiologists for the presence of the double contour sign, tophus, erosion, effusion, synovial hypertrophy, and synovitis. Cartilage thickness and tophus diameter were also measured. Inter-reader reliability was assessed using Cohen’s kappa (ƙ) and intra-class correlation coefficients (ICC). Binary logistic and linear regression models were used to determine between-group differences in the ultrasound features. A stepwise linear regression was used to determine which ultrasound features were independently associated with gout compared with asymptomatic hyperuricaemia.

Results: Inter-reader reliability was moderate for the presence of the double contour sign, tophus, erosion, synovial hypertrophy and effusion (ƙ=0.42 to 0.59), good for synovitis (ƙ=0.66) and excellent for cartilage thickness and tophus diameter (ICC=0.81 and 0.86 respectively). Compared to normouricaemic control participants, participants with gout and with asymptomatic hyperuricaemia had more frequent double contour sign (Table, odds ratio (OR) 3.91, P=0.011 and OR 3.81, P=0.009, respectively). Participants with gout also had more erosion (OR 10.13, P=0.001) and synovitis (OR 9.00, P<0.001) and had greater tophus diameter (0.00mm vs. 1.68mm, P=0.035). There was no significant difference in cartilage thickness between groups. More severe erosion and synovitis grades and a less severe effusion grade were independently associated with a diagnosis of gout compared with asymptomatic hyperuricaemia (R² for model = 0.65, p < 0.001).

Conclusion: Urate deposition, synovitis and bone erosion are common at the 1MTPJ in people with gout, even in the absence of flare. Furthermore, although individuals with asymptomatic hyperuricemia lack ultrasound features of inflammation or structural joint changes, they demonstrate a similar frequency of urate deposition. These data support the concept that gout is a disease of chronic inflammation in response to intra-articular urate crystal deposition.