Symptom Experience and Content Validity of the Psoriasis Symptom Scale (PSS) in Patients with Generalized Pustular Psoriasis (GPP).

Introduction: We sought to understand key symptoms of generalized pustular psoriasis (GPP) and to confirm the relevance to patients and content validity of the Psoriasis Symptom Scale (PSS) in GPP.

Methods: A targeted literature review and clinical expert interviews were conducted as background research. Patients were interviewed individually (involving concept elicitation and cognitive interviews), and a separate patient workshop was conducted to determine disease-specific symptoms of importance.

Results: Seven participants with moderate (n = 4), severe (n = 2), and mild (n = 1) GPP and clinician diagnosis were interviewed. During concept elicitation, all participants indicated that pustules may underlie other symptoms. Symptoms reported by all patients were pain, redness, itch, burning, and discomfort. The PSS symptoms of pain, itching, burning, and redness were reported by ≥ 86% of patients as most frequently experienced. Upon debriefing, the PSS was well understood. Relevance and importance of these symptoms was confirmed in the GPP patient workshop.

Conclusion: Participant feedback found the PSS measure to be relevant and easy to understand. The symptoms included in the instrument, pain, redness, itch, and burning, were most frequently reported, important, and well understood by patients. Study results provided support for the content validity of the PSS for use as endpoints in GPP clinical trials.