The effects of structural damage on functional disability in psoriatic arthritis

Functional outcomes are central in patients with chronic inflammatory musculoskeletal diseases. In a secondary data analysis of the GO-REVEAL trial (NCT00265096), we investigated wether structural damage is linked to functional impairment in patients with psoriatic arthritis (PsA), a link that is still elusive in this disease.

We analysed 363 patients enrolled in the GO-REVEAL study and obtained modified Sharp/van der Heijde Scores (mSvdHS) from X-rays performed at baseline, after 24, 52 and 104 weeks. Using longitudinal analyses, we assessed the effect of total mSvdHS (and its subscores, joint space narrowing (JSN) and erosions (ERO)) on functional status (measured by the Health Assessment Questionnaire) in all patients and in those attaining remission (n=117). Furthermore, we analysed wether structural damage reduces the responsiveness of functional limitations to treatment in a subgroup of responders who had functional impairment at baseline (n=67). Additionally, internal and external validation analyses were performed.

The effect of damage on function was seen in the disease activity-adjusted models using total mSvdHS (p=0.005), JSN (p=0.019) and ERO (p=0.001) as well as in the remission analyses for mSvdHS (p=0.029) and JSN (p=0.010), respectively. Functional responsiveness was limited by increasing total mSvdHS (p=0.010), JSN (p=0.002) and ERO (p=0.040). The results were validated using other functional outcomes and in an independent clinical cohort.

In PsA, structural damage, particularly JSN, has implications for physical function. Functional outcomes have an irreversible component that is strongly related to the extent of joint destruction. This needs to be considered when targeting functional outcomes in clinical practice.