Combination Approach Needed to Accurately Measure Quality of Life in Patients with Psoriatic Arthritis

New research designed to measure the accuracy and validity of a trio of tools designed to assess quality of life in psoriatic arthritis patients indicates that none are comprehensive enough to be used alone and suggests that caregivers use 2 of the assessments in tandem.

The study cohort included 503 psoriatic arthritis patients (286 men, 217 women) from 15 different countries with a mean age of 50.8 years (standard deviation, 13.1 years) and a mean disease duration of 9.8 years (standard deviation, 9.9 years). All patients, as part of an effort to develop new composite measures of psoriatic arthritis severity, completed 3 existing measures: the Psoriatic Arthritis Quality of Life (PsAQol), the Ankylosing Spondylitis Quality of Life (ASQoL), and the Dermatology Life Quality Index (DLQI).

The authors of the new paper, who presented their results at the 2015 meeting of the American College of Rheumatology and Association of Rheumatology Health Professionals, used Rasch analysis to determine different aspects of each assessment’s performance, including the internal consistency of each measure, the cross-cultural validity in different regions of the world and the relative ability of each to assess joint and skin aspects of patient experience.

The different measures tended to perform consistently regardless of patient age or sex, but performance varied with patient geography. The PsAQoL satisfied the expectations of the Rasch model in North American patients but not patients in South America, the UK, the rest of Europe or Asia. The ASQoL, on the other hand, only managed to satisfy Rasch model expectations among patients in the UK, while the DLQI did so for both patients in the UK and North America but not those in the rest of the world.

The DLQI performed better than the PsAQoL in assessing how aspects of psoriatic arthritis related to the skin and the joints affected patient quality of life and it did better than the ASQoL in assessing how skin health affected quality of life. The ASQoL, on the other hand, did better than the other tools in determining how psoriatic arthritis’ impact on the spine affected quality of life (F(1,66) = 13.76, p<0.001).

‘The data suggest that PsAQoL does not cover the full spectrum of health-related quality of life in psoriasis,” the study authors concluded. “Conversely, DLQI does not cover the full spectrum of health-related quality of life of articular disease in psoriatic arthritis. PsAQoL, (or ASQoL) and DLQI complement each other in capturing both joint and skin aspects of health-related quality of life.”

The data from all the patients was collected as part of the GRACE project, which used even more data from those same to engineer composite measures of disease activity in psoriatic arthritis patients. The investigators in that project collected information from all 503 patients in every domain of disease activity shown by randomized trials to be significant and then worked backward from that information to make the psoriatic arthritis disease activity score (PASDAS) and the arithmetic mean of desirability functions (AMDF). The investigators then compared the performance of the new indices against older indices in the study population.

“Although all measures performed well, compared with existing indices, PASDAS was better able to discriminate between high and low disease activity,” they wrote in the Annals of Rheumatic Disease before noting the need for more testing of the new composites.