Functional Impact of Structural Damage in Psoriatic Arthritis: Insights from a Prospective Cohort Study

To examine the association between radiographic structural damage and physical function (PF) in psoriatic arthritis (PsA).

Data were analyzed from a large longitudinal PsA cohort. PF was measured using the Health Assessment Questionnaire (HAQ, 0-3) and Short Form-36 PF subscale (SF-36, 0-100); radiographic joint damage was measured using the modified Steinbrocker score (mSS, 0-168). Associations between PF and mSS were analyzed using linear mixed models. We also evaluated the impact of the presence of any damaged joint (grade 2-4), joint damage by individual grades, and the number of damaged joints (grade 2-4) per patient on PF.

Of 1,177 patients (mean ± SD age 44.61 ± 12.76 years; 55.8% men), baseline mSS was 2 (interquartile range [IQR] 0-8.5), HAQ was 0.62 (IQR 0.12-1.12), and SF-36 PF was 60 (IQR 35-85). Higher mSS was significantly associated with worse SF-36 PF (β = -0.10; 95% confidence interval [CI] -0.15 to -0.05) and HAQ (β = 0.003; 95% CI 0.002 to 0.004) after controlling for swollen joint count, sex, and disease duration. The number of damaged joints was associated with worse SF-36 PF (β = -0.23; 95% CI -0.38 to -0.08) and HAQ (β = 0.005; 95% CI 0.002 to 0.009). The presence of a damaged joint (grade 2-4) alone did not impact PF. However, the presence of a joint with grade 4 destruction was associated with substantially worse SF-36 PF (β = -3.04; 95% CI -5.93 to -0.15) and HAQ (β = 0.09; 95% CI 0.03 to 0.15). Increasing counts of grade 4 joints demonstrated a strong dose response with SF-36 PF (β = -0.54; 95% CI -0.81 to -0.26) and HAQ (β = 0.01; 95% CI 0.01 to 0.02).

Radiographic structural damage, particularly severe joint destruction, is independently associated with impaired PF in PsA, highlighting the importance of early detection and prevention of damage.