Analysis of the relationship between psoriasis symptom severity and quality of life, work productivity, and activity impairment among patients with moderate-to-severe psoriasis using structural equation modeling

Colin Lewis-Beck,¹ Safiya Abouzaid,² Lin Xie,³ Onur Baser,^3,4 Edward Kim<sup>5

1</sup>Freddie Mac, Washington, DC, ²Eisai, Woodcliff Lake, NJ, ³STATinMED Research, ⁴The University of Michigan, Ann Arbor, MI, ⁵Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA

Background: Plaque psoriasis is a chronic disease characterized by scaly plaques on the skin that can itch and bleed. Psoriasis covering over 10% of the body is classified as moderate to severe, and can impact patient quality of life.
Objectives: To assess the relationship between plaque psoriasis self-reported severity symptoms and health-related quality of life, work productivity, and activity impairment among patients with moderate-to-severe psoriasis.
Methods: The study sample included 199 patients recruited from internet panels, of which 179 respondents had plaque psoriasis and 20 had plaque and inverse psoriasis. Itching, pain, and scaling symptoms were studied. A structural equation modeling framework was used to estimate the effect of these symptoms on patient outcomes. First, each severity variable was regressed on a set of covariates to generate a predicted severity score. These predicted values were placed in a second-stage model with patient mental and physical scores (Short-Form 12 questionnaire), work productivity, and activity impairment indicators as dependent variables.
Results: Itching severity had a marginal negative effect (P < 0.06) on patients' Short-Form 12 physical and mental component scores. Pain severity also negatively affected physical and mental health scores (P < 0.02). Patients were more likely to miss work because of itching (odds ratio [OR]: 2.31, 95% confidence interval [CI]: 1.30, 4.10), pain (OR: 1.78, 95% CI: 1.25, 2.52), and scaling (OR: 2.15, 95% CI: 1.31, 3.52) symptoms. These symptoms also lowered self-reported productivity. As itching (OR: 1.74, 95% CI: 1.03, 2.95), scaling (OR: 1.84, 95% CI: 1.16, 2.90), and pain symptoms (OR: 1.53, 95% CI: 1.12, 2.09) increased, so did the odds that a patient would be less productive at work.
Conclusion: Plaque psoriasis significantly affects patient quality of life. In addition to greater mental and physical pain, patients are more likely to miss work and have diminished productivity as symptom severity increases.

Keywords: psoriasis, severity, activity impairment, work productivity loss, structural equation modeling