Development of the Psoriasis Symptoms Scale (PSS) in patients with moderate-to-severe psoriasis: qualitative and quantitative analyses

Abstract

Background: Psoriasis is a chronic inflammatory skin disease.

Objective: To establish content validity and assess psychometric properties of the Psoriasis Symptoms Scale (PSS) in patients with moderate-to-severe psoriasis (Ps).

Methods: The PSS is an eight-item patient-completed questionnaire assessing symptoms (itch, pain, stinging, burning), signs (redness, scaling, cracking), and discomfort. Content validity was established during interviews of patients (n = 14) with Ps. PSS Symptoms and Signs domain scores were evaluated for reliability, construct validity, and responsiveness using data from a clinical study (NCT02899988) in Ps (n = 205).

Results: Patients confirmed content validity; the PSS was understandable and relevant. Cronbach’s alphas were 0.84 (Symptoms) and 0.86 (Signs), demonstrating internal consistency reliability. Test–retest reliability was confirmed in patients before receiving study drug (intraclass coefficient: 0.82 [Symptoms]; 0.81 [Signs]). Convergent and discriminant validity were demonstrated at baseline and Week 16 by large (≥0.50) correlations between PSS Symptoms and Signs domain scores and Dermatology Life Quality Index total and symptoms and feelings domain scores, and small (<0.30) correlations with Short Form-36 Mental Component Summary score, respectively. Symptoms and Signs scores responded to clinical changes (p < .001).

Conclusions: The PSS Symptoms and Signs domains are valid and reliable assessments of patient-reported symptoms and signs, useful for assessing treatment efficacy.

Keywords:

• Psoriasis
• patient-reported outcomes
• symptoms
• signs
• Psoriasis Symptoms Scale

Acknowledgements

Writing and editorial assistance in the preparation of this manuscript were provided by Lori Kornberg, PhD and Noelle Gasco, BA (Syneos Health, Raleigh, NC).

Disclosure statement

A.W. Armstrong has served as investigator, advisor, and/or consultant to AbbVie, Janssen, Novartis, Eli Lilly and Company, Regeneron, Sanofi, Leo, Science 37, Modernizing Medicine, and Ortho Dermatologics. M. Anatchkova is an employee of Evidera. Evidera received research study support from Eli Lilly and Company. J.-L. Poon was an employee at Evidera at the time that this work was performed; she is currently an employee of Eli Lilly and Company and owns stock. E. Edson-Heredia, A. Naegeli, R. Burge, L. Sun, and B. Zhu are full-time employees of Eli Lilly and Company and own stock. K.W. Wyrwich was an employee of Eli Lilly and Company at the time the work was performed and owns stock.

Data availability

Lilly provides access to relevant anonymized patient level data from studies on approved medicines and indications as defined by the sponsor specific information on www.clinicalstudydatarequest.com. For details on submitting a request, see the instructions provided at www.clinicalstudydatarequest.com.

Additional information

Funding

This study was funded by Eli Lilly and Company, Indianapolis, Indiana, USA, which contracted with Evidera (Bethesda, Maryland) for the design and analysis of the content validation portion of this work.