Background/Purpose: Psoriatic arthritis (PsA) significantly affects physical function (PF), which is influenced by both disease activity and structural damage. Despite its clinical importance, there is limited quantitative data on how radiographic damage impacts PF in PsA. This study aimed to assess the relationship between radiographic damage and PF in PsA patients.

Methods: We analyzed data from a large, prospectively enrolled cohort of PsA patients followed since 1978. Assessments were performed every six months, including evaluations of disease activity, patient-reported outcomes, and treatment details. Radiographs were obtained every two years. Disease activity was measured by swollen joint count (SJC), and PF was assessed using the Health Assessment Questionnaire (HAQ; 0-3) and the Short Form 36 (SF-36) PF domain score (0-100). Radiographic damage was scored using the modified Steinbrocker scoring system (mSS, 0-168). Only patients with PF data collected within three months of their radiographs were included in the analysis.Baseline characteristics at enrollment were summarized. Cumulative probability plots were created to illustrate visit-to-visit changes in both mSS scores and PF scores. Multivariable linear mixed models (LMM) were used to examine the association between PF measures (HAQ and SF-36 PF) and mSS, adjusting for covariates including age at PsA diagnosis, disease activity (SJC at the time of radiographs), sex, and disease duration. Further, we assessed the severity of joint damage (any joint graded 2, 3, or 4) and the number of severely damaged joints (graded 2, 3, or 4) per patient for their association with SF-36 PF using LMM, adjusting for SJC, age at PsA diagnosis, sex, and disease duration.

Results: Among 1,177 patients, the mean age at enrollment was 44.61 ± 12.76 years, and 657 (55.8%) were male. The median mSS was 2 (IQR 0, 8.5), HAQ was 0.62 (IQR 0.12, 1.12), and SF-36 PF score was 60 (IQR 35, 85) at enrollment. The mSS change scores in relation to the corresponding HAQ and SF-36 PF change scores are presented in Figure 1.The mSS showed significant associations with both HAQ (b = 0.003, 95% CI 0.002 to 0.004) and SF-36 PF (-0.10; 95% CI -0.15 to -0.05), after adjusting for disease activity (SJC), age at PsA diagnosis, sex, and disease duration (Table 1). While the presence of a damaged joint was not significantly associated with PF, the number of severely damaged joints (graded 2, 3, or 4) per patient was significantly associated with both HAQ (b = 0.01, 95% CI 0.001 to 0.01) and SF-36 PF (-0.22, 95% CI -0.37 to -0.07).

Conclusion: Structural damage, as quantified by the mSS , is significantly associated with physical function in PsA, independent of disease activity and other factors. Specifically, a one-unit increase in the mSS corresponds to a 0.003 increase in HAQ and 0.10 decrease in SF-36 PF. While the presence of a single damaged joint does not notably affect PF, the cumulative number of severely damaged joints is significantly associated with a decline in PF. These findings underscore the importance of early diagnosis and effective management of PsA to preserve physical function and prevent structural damage.

Figure 1: Cumulative probability plots reflecting visit-to-visit change scores of the modified Steinbrocker score with SF-36 PF (A) and HAQ (B)

Table 1: Association between mSteinbrocker score and physical function using multivariable linear mixed models

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/quantifying-functional-impact-of-structural-damage-in-psoriatic-arthritis-insights-from-a-long-term-prospective-cohort/