Background. The clinical manifestations of psoriatic arthritis (PsA) and rheumatoid arthritis (RA) differ significantly. Despite improved clinical outcomes in PsA and RA, both diseases still have a significant impact on patients’ lives. Whether these differences in clinical manifestations lead to a difference in disease impact between PsA and RA at presentation and after treatment is unknown. 

Objective. To determine the difference in disease impact, measured with patient-reported outcomes (PROs), between matched PsA and RA patients at diagnosis and after one year of treatment.

Methods. PsA patients with an oligo-arthritis or polyarthritis from the Dutch southwest Early PsA cohoRt (DEPAR) and RA patients, according to the 1987 and/or 2010 criteria, from the treatment in the Rotterdam Early Arthritis CoHort trial (tREACH) were included. The difference in disease impact between PsA and RA was measured with the following PROs: pain, fatigue, activity limitation and health impact. Propensity scores (including swollen and tender joints as disease activity measure) were used to match PsA and RA patients, after which inversed probability weights (IPW) were calculated. Linear regression models with IPW were used to measure the difference in disease impact.

Results. 581 PsA patients and 422 RA were included. At diagnosis, PsA patients reported more mental health problems (-12.37 units (95% CI 5.67 to 19.01, p<0.001) on the SF36 Mental Component Summary score, and reported worse general health (+9.28 units (95% CI -14.22 to -4.34, p<0.001) on general health Visual Analogue Scale (Figure 1). After one year of treatment, PsA patients still had worse mental quality of life (-4.22 units (95% CI 1.92 to 6.53), p<0.001) than RA patients. No differences were seen in the other PRO domains.    

Conclusion. The disease burden in early PsA is higher compared to matched early RA patients, especially with regard to mental HRQoL, both at diagnosis and after one year of treatment. This higher burden of disease may well be due to the extra-articular disease manifestations in PsA patients. 

Figure 1. Differences in PROs between RA and PsA patients at diagnosis 

Values shown are the mean differences in PROs between RA and PsA at diagnosis with the corresponding 95% confidence interval. For example, RA patients scored on average 4.65 points lower on a VAS pain compared to PsA patients.

In the adjusted IPW the following variables were added to the model: sex, education level, BMI, SJC-44, TJC-53, CRP and ESR. 

Table 1. Baseline characteristics of RA and PsA patients