The Psoriasis Symptom Diary: development and content validity of a novel patient‐reported outcome instrument

Abstract

Chronic plaque psoriasis has a profound impact on a patient's daily life. To understand the effects of psoriasis treatments, it is essential to assess the patient's experience of symptoms and how they impact their daily life. The goal of this study was to develop and establish the content validity of a new patient reported outcome (PRO) psoriasis measure. The Psoriasis Symptom Diary was developed by (i) identifying key plaque psoriasis-related symptoms and impacts through qualitative patient interviews (n=29); (ii) developing an initial set of items that captured the key patient experiences; and (iii) conducting cognitive interviews to test patient understanding of items selected for inclusion in the new psoriasis symptom measure (n=16). Patients noted a variety of symptoms, with plaque-related pain (including related concepts of burning and stinging), changes in skin appearance, and itching reported by all patients. Patients also expressed notable embarrassment and avoidance of social situations, due to the appearance of plaques, and limited mobility. The Psoriasis Symptom Diary assesses the severity and impact of symptoms using a 24-hour recall period to reduce recall bias and error. The Psoriasis Symptom Diary was developed to assess important symptoms and disease-related impacts in a manner consistent with guidelines for establishing the content validity of new PRO instruments. Following quantitative psychometric testing, the Psoriasis Symptom Diary may support efficacy endpoints in clinical trials.