Features of the Achilles tendon, paratenon, and enthesis in inflammatory rheumatic diseases

We analyzed the ultrasonographic (US) features of the Achilles tendon (AT), paratenon (AP), and enthesis in patients with axial spondyloarthropathies (SpA) and rheumatoid arthritis (RA), and compared these to healthy subjects. Relationships between these findings and clinical and functional parameters were identified.

The study included 40 axial SpA and 27 RA patients, as well as 30 healthy subjects. Clinical evaluation relied on the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath AS Functional Index (BASFI), AS Quality of Life Questionnaire (ASQoL), Disease Activity Score 28 (DAS28), and Health Assessment Questionnaire (HAQ), as well as on a visual analog scale (VAS) for entheseal pain and the Madrid Sonographic Enthesistis Index (MASEI). Separately, AT thickness, AP thickness, and echogenicity were examined bilaterally with US in 194 ankle regions.

The fibrillar pattern of the AT was damaged in axial SpA patients compared to RA patients and healthy subjects (p < 0.001). The AT was thicker in axial SpA patients than in RA patients and healthy subjects (p < 0.05). The AP was thicker in axial SpA patients (p < 0.05). There were positive correlations of BASDAI and BASFI scores with the Achilles enthesitis total score (r = 0.523, p = 0.001 and r = 0.533, p = 0.001, respectively). In the multiple linear regression model, only age continued to show an effect on the Achilles enthesitis total scores in axial SpA patients (B = 0.091, β = 0.417, p = 0.011). The AT thickness was consistently positively correlated with height in axial SpA patients (B = 0.059, β = 0.482, p = 0.004).

The AT thickness was affected much more by the height of patients with axial SpA in comparison to RA patients and healthy subjects. Age was an independent factor for high Achilles enthesitis scores only in axial SpA.