Background/Purpose: Tendon involvement in the lower limbs in gout is frequent.  Tophus deposition to the Achilles tendon (AT) has been reported, however, data describing ultrasound (US) lesions to specific anatomical zones of the AT is limited.  The aim of the study was to investigate frequency and distribution of US lesions of the AT in people with tophaceous gout compared to age and sex matched controls.  

Methods: Twenty-four participants with tophaceous gout and 24 age- and sex-matched control participants without gout or other arthritis were recruited.   All participants underwent US examination, using both greyscale and power Doppler (PD) technique by a musculoskeletal radiologist who was blinded to diagnosis.  The AT was divided into three anatomical zones (zone 1: insertion, zone 2: pre-insertional and zone 3 proximal to the mid-section).  US lesions were scored using a semi-qualitative scoring system assessing tophus, tendon echogenicity, tendon vascularity, tendon morphology, enthesis, bursal morphology and entheseal bone profile.  All US scanning techniques and lesion definitions were used as proposed by the OMERACT ultrasound task force.  Scans were scored independently by two musculoskeletal radiologists, blinded to diagnosis and each other’s scores, with kappa levels of agreement ranging between 0.77 to 1.00. As lesions were nested within participants, a general estimating equation approach was used to data analysis.  All tests were two-tailed, with p < 0.05 considered significant.

Results: The table shows the percentage of US lesions present in each group and defined by the zone of the AT. Tophus deposition was observed in the AT of 73% of participants with tophaceous gout and not observed in control participants (p < 0.01).  Intratendinous hyperechoic spots and intratendinous PD signal were also more frequent in participants with tophaceous gout compared to control participants (p < 0.01 for both).  Frequency of entheseal lesions, calcaneal lesions and AT thickness did not differ between groups. In participants with gout, there was no significant difference in distribution of tophi or intratendinous power Doppler signal at different zones. In contrast, intratendinous hyperechoic spots were most commonly observed in zone 1 and were least commonly observed in zone 3 of the AT.

Conclusion: The Achilles tendon is frequently involved in people with tophaceous gout. Ultrasound features of intratendinous urate deposition and inflammation are commonly observed.  Table: Percentage of ultrasound lesions present between case and control participants