Incremental effects of comorbidity on quality of life in patients with psoriatic arthritis.

Objective: To assess the added effect of comorbidity on quality of life (QOL) in psoriatic arthritis (PsA).

Methods: Between 2006 and 2012, 631 patients were recruited from the University of Toronto PsA Clinic. Using the clinical database, we ascertained the frequency of 15 comorbidities. The Medical Outcomes Study Short Form-36 (SF-36) physical (PCS) and mental component (MCS) summary scales were used to assess QOL. Linear regression analyses were conducted to estimate the magnitude of the association between number and type of comorbidities and PCS and MCS scores, after adjustment for disease-related and sociodemographic variables.

Results: Prevalence of comorbidity was high, with 42% of patients having 3 or more comorbid conditions. After adjustment for inflammatory disease-related and sociodemographic factors, a history of 3 or more comorbid conditions accounted for only 2% and 1% of the R(2) value explained in PCS and MCS scores, respectively. In terms of added burden, type of comorbid condition was more significant than number of comorbidities. After adjustment for disease-related and sociodemographic factors, fibromyalgia (FM), neurological disorders, and obesity jointly accounted for 6% of R(2) value explained in PCS scores, while FM and depression/anxiety jointly accounted for about 9% of the R(2) explained in MCS scores. The point decrease in PCS and MCS scores associated with each of these disorders was clinically significant. The 11 other comorbid conditions failed to achieve statistical significance in the models.

Conclusion: The added effect of comorbidity on patient-reported physical and mental health in PsA was more related to type of comorbidity than number of comorbidities.