The shrinking toe sign in gout

Objective: To describe the frequency, clinical presentation and understand the pathophysiology of toe shortenings during urate-lowering treatment (ULT) of gout, a feature we called the shrinking toe sign.

Methods: Sequential foot photographs and radiographs of 1141 consecutive gouty patients followed-up for at least 6 months under ULT were retrospectively scrutinized. Features from patients with toe shortenings were extracted from anonymized files. Tophi adjacent to the shortening sites were semi quantified on foot photographs and toe shortenings were measured on radiographs with the Corel draw software (Corel corporation, Canada). Measurement concordance was assessed by concordance correlation coefficients (CCC) and correlation between tophus scores and toe shortenings was analyzed by using linear model with a patient random effect. 97 patients who did not develop toe shortening during ULT were analyzed as controls.

Results: Shrinking toes were observed in 10 patients (0.9%) with tophaceous gout at joints with baseline destructive arthropathy. The first and second toes and metatarsophalangeal joints were predominantly involved. The sign was observed after serum urate had been lowered below the 300 and 360 µmol/l targets, in 8 and 2 patients, respectively. Measured shortenings (CCC: 0.99) correlated (p < 10^-4) with decreases in tophus score (CCC: 0.91). Sequential radiograph analysis revealed that toe shortening was mainly due to lytic bone collapse during articular tophus dissolution. Comparison with controls showed that the sign developed in severe gout and in joints with more severe erosion score at baseline.

Conclusion: The shrinking toe appears as rare feature of severe tophaceous gout, triggered by dissolution of bone-replacing tophi. Our findings reinforce the need to treat gout early, before destruction of bone scaffold by extensive tophi, as MSU crystal dissolution by ULT may further weaken these areas and induce their collapse.