Background/Purpose: The involvement of bone and joints is widely recognized in gout.  However, soft tissue involvement is less well defined. Dual energy computed tomography (DECT) is a recently developed technology that enables detection of urate deposits.  The aim of this study was to examine the frequency and patterns of tendon and ligament involvement in patients with gout using DECT.

Methods: Ninety-two patients with tophaceous gout had a study visit including DECT scan of both feet.  Two readers scored the DECT scans for urate deposition at 20 tendon/ligament sites and 42 bone sites (total 1,840 tendon/ligament sites and 3,864 bone sites).  For affected tendons and ligaments, involvement was recorded as entheseal and/or non-entheseal (entheseal involvement was defined as urate deposition at the point of tendon/ligament insertion into bone). Inter-reader agreement for involvement at tendon/ligament sites was 88.0% and Cohen’s kappa was 0.58, and at bone sites was 94.7% and Cohen’s kappa was 0.77.  For a stringent analysis, urate deposition was considered present at each site only if reported by both readers.

Results: Urate deposition was observed in 199/1840 (10.8%) tendon/ligament sites and in 399/3864 (10.3%) bone sites (p=0.60). The Achilles tendon was the most frequently involved tendon/ligament site (39.1% all Achilles tendons), followed by the peroneal tendons (18.1%) (Figure).  Tibialis anterior and the extensor tendons were involved less frequently (7.6-10.3%), and the flexor tendons, plantar fascia and deltoid ligaments were involved infrequently (<5%) (p<0.0001 between sites). In those 72 Achilles tendons with urate deposition, 27 (38%) had only non-entheseal involvement, 29 (40%) had both entheseal and non-entheseal involvement, and 16 (22%) had only entheseal involvement. In contrast, entheseal involvement was less frequent at the other 127 affected tendon/ligament sites; 102 (80.3%) had only non-entheseal involvement, 25 (19.9%) had both entheseal and non-entheseal involvement, and 0 (0%) had only entheseal involvement (p<0.0001 compared with Achilles tendon site).

Conclusion: Urate deposition is observed in tendon and ligament sites in patients with gout using DECT. The Achilles tendon and enthesis are major sites of involvement in gout.  The patterns of urate deposition at certain tendon/ligament sites suggest that biomechanical strain or other local factors may contribute to formation of urate crystals.

Figure: Volume rendered DECT image demonstrating urate deposition in the Achilles and peroneal tendons.  Large adjacent tophi are present. Note normal tibialis anterior tendon.