Background/Purpose: Psoriatic arthritis (PsA) is a progressive disease bringing substantial socioeconomic burden. Gradual loss of productivity (PL) and daily activities can be modified by effective therapy, e.g. biological treatment (BT).

Methods: We described the cohort and methods elsewhere. 228 PsA patients diagnosed with CASPAR criteria were followed over 873 appointments in 6-month intervals. Activity (AI) and work impairment (WI) were assessed using WPAI questionnaire. Predictors of WI were explored with linear mixed-effect regression (ME) and statistical differences between groups using Kruskal-Wallis test. PL was monetized via Human Capital Approach (HCA; costs until retirement at 62.7 years; discount rate 3%) with average gross wage of €1493.

Results: 53.5% patients were working and 25.4% were disabled. Mean baseline AI and WI in working patients (± SD) were 0.28 (± 0.24) and 0.33 (± 0.32). Similarly to HAQ score (0.74 ± 0.70), WI and AI worsened with growing PsA activity measured either by DAPsA score or cDAPsA (excluding serum CRP) with p ≤ 0.0001. The mean time to retirement was 14.0 ± 9.9 years.

38.2% patients had BT (anti-TNF) in the 12 months prior to enrolment with the mean costs of €981 per patient-month. Compared to non-BT population, BT patients were younger (50.7 vs. 59.4) and more frequently disabled (17.1% vs. 8.3%). They had lower DAPsA at baseline (14.43 vs. 17.14; p = 0.02) due to lower serum CRP (5.72 vs. 7.12; p = 0.0035) contrarily to cDAPsA which differed neither in baseline (8.60 vs. 9.97; p= 0.075) nor in longitudinal population (8.2 vs. 9.5; p= 0.056). Number of swollen joints dropped in the longitudinal population (1.02 vs. 1.23; p = 0.0015) while WI raised (0.38 vs. 0.41; ≤ 0.0001).

HAQ, AI and time from diagnosis were the best predictors of WI. ME models translated into productivity costs using HCA showed that increase in either HAQ or AI (as sole predictors) by 0.1 represent a growth of PL by €2387 or €5367 (Figure 1). In the most robust model, increase of HAQ and AI together by 0.1 correspond to the growth of indirect costs by €6212. Both DAPsA and cDAPsA were significant, yet weak predictors of WI.

Conclusion: In view of the BT indication criteria (severity, failure of previous treatment), the clinical parameters of the BT population suggest that BT effectively slows PsA progression. Primary response was observed as attenuation of acute inflammation measured by CRP. HAQ and AI are the best predictors of WI in PsA. Therefore, we can conclude that decreasing HAQ, e.g. via more effective BT, will undoubtedly increase working productivity and thus decrease productivity losses in PsA patients.

Figure 1. Fitted values of productivity costs predicted by HAQ or Activity impairment (WPAI questionnaire) using the mixed regression model

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-relationship-between-biological-therapy-work-productivity-and-activity-impairment-in-patients-with-psoriatic-arthritis-prospective-multicentre-observational-study/