Understanding the Relationship Between Pruritus Severity and Work Productivity in Patients With Moderate-to-Severe Psoriasis: Sleep Problems Are a Mediating Factor

February 2016 | Volume 15 | Issue 2 | Original Article | 183 | Copyright © February 2016


A.B. Kimball MD MPH,a E. Edson-Heredia MPH,b B. Zhu PHD,b J. Guo MS,b T. Maeda-Chubachi MD PHD,b W. Shen PHD,b and M.T. Bianchi MD PHDa

aHarvard Medical School, Boston, MA
bLilly Research Labs, Indianapolis, IN

Abstract
BACKGROUND: Psoriasis is a debilitating skin disease associated with substantial pruritus, work impairment, and sleep disturbance.
OBJECTIVE: This study evaluated associations between pruritus and work productivity, and the role of sleep problems as a possible mediator of the relationship between the two.
METHODS AND MATERIALS: Data from a pruritus visual analog scale (Itch VAS), the Medical Outcomes Study Sleep Scale (MOS-SS), and the Work Productivity and Activity Impairment Questionnaire (WPAI) were collected in a phase 2 clinical trial in patients with psoriasis treated with ixekizumab or placebo. Mediating effects of sleep were tested in multiple regressions with pruritus severity (independent variable) and work productivity (dependent variable). Sobel tests evaluated the significance of sleep’s effect.
RESULTS: Several MOS-SS domains were significantly associated with the WPAI presenteeism, work productivity, and activity impairment scores, and decreased the effect of pruritus. Sobel tests indicated that the Sleep Problems Index I had a significant effect (P<.05) in mediating the relationship between pruritus and presenteeism, work productivity, and activity impairment.
CONCLUSION: Sleep may mediate the role of pruritus on work productivity, but both factors appear to have independent negative effects on work.

J Drugs Dermatol. 2016;15(2):183-188.

INTRODUCTION

CThe burden of psoriatic disease is substantial and includes pruritus, pain, sleep disturbance,1 and work productivity impairment.2 However, itch as a mediator of symptoms has been underexplored, especially since pruritus does not always correlate with disease severity. Consistent with this hypothesis, one study recently demonstrated that sleep was not affected by disease severity,3 as measured by the PASI score, but was affected by symptoms of itching (pruritus) and obstructive sleep apnea (psoriasis patients are frequently overweight or obese, and obstructive sleep apnea is often undiagnosed in patients with insomnia).4 Zachariae et al.5 recently evaluated sleep as a mediating factor between affective pruritus severity and domains of depression, general distress, and health-related quality of life in psoriasis patients and found sleep mediated the association between pruritus severity and general distress, as measured by the Brief Symptom Inventory.
Psoriasis patients are also known to experience substantial work presenteesim, which improves as the disease regresses.2,6,7 Given that insomnia is associated with presenteeism,8 it is important to explore potential relationships between pruritus, sleep impairment, and work productivity activity impairment. These relationships are not well understood and are likely to be complicated, but they are critical in assessing the burden of disease and the value of therapy to patients affected by these conditions. We conducted a post hoc analysis to determine any associations between pruritus severity and the variables of sleep problems and work productivity activity impairment. We also evaluated the role of sleep quality as a possible mediator.

METHODS AND MATERIALS

Data Source

Data were from a double-blind, randomized, placebo-controlled, phase 2 clinical trial that has been previously reported.9 Briefly, 142 adult patients with chronic moderate-to-severe plaque psoriasis (for ≥6 months prior to randomization) received subcutaneous 10, 25, 75, or 150 mg of ixekizumab or placebo at 0 (baseline), 2, 4, 8, 12, and 16 weeks. The primary outcome was the proportion of patients with at least a 75% reduction in the Psoriasis Area-and-Severity Index (PASI) score from baseline at 12 weeks. The PASI was also assessed at weeks 8 and 16. Neither obstructive sleep apnea nor sleeping pill usage was exclusion criteria in this study.
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