Association of Structural Entheseal Lesions With an Increased Risk of Progression From Psoriasis to Psoriatic Arthritis

Objective To test whether the presence of structural entheseal lesions in psoriasis patients influences the risk of progression to psoriatic arthritis (PsA). Methods We conducted a prospective cohort study of psoriasis patients without clinical evidence of musculoskeletal involvement who underwent baseline assessment of structural entheseal lesions and volumetric bone mineral density (vBMD) at entheseal and intraarticular sites by high‐resolution peripheral quantitative computed tomography. Adjusted relative risks of developing PsA associated with baseline vBMD and the presence of structural entheseal lesions were calculated using multivariable Cox regression models. Results The cohort included 114 psoriasis patients (72 men and 42 women) with a mean ± SD follow‐up duration of 28.2 ± 17.7 months, during which 24 patients developed PsA (9.7 per 100 patient‐years [95% confidence interval (95% CI) 6.2–14.5]). Patients with structural entheseal lesions were at higher risk of developing PsA compared to patients without such lesions (21.4 per 100 patient‐years [95% CI 12.5–34.3]; hazard ratio [HR] 5.10 [95% CI 1.53–16.99], P = 0.008). With respect to vBMD, a 1‐SD increase in entheseal, but not intraarticular, vBMD was associated with an ~30% reduced risk of progression to PsA. Especially, higher cortical vBMD at entheseal segments was associated with a lower risk of developing PsA (HR 0.32 per 1 SD [95% CI 0.14–0.71]), and the association remained robust after multiple imputation of missing data (HR 0.64 [95% CI 0.42–0.98]). Conclusion The presence of structural entheseal lesions as well as low cortical vBMD at entheseal segments are associated with an increased risk of developing PsA in patients with psoriasis.