Measurement Properties of the Psoriasis Symptom Inventory Electronic Daily Diary in Patients with Moderate to Severe Plaque Psoriasis.

OBJECTIVES

The Psoriasis Symptom Inventory (PSI) is a patient-reported outcome instrument that measures the severity of psoriasis signs and symptoms. This study evaluated measurement properties of the PSI in patients with moderate to severe plaque psoriasis.

METHODS

This secondary analysis used pooled data from a phase 3 brodalumab clinical trial (AMAGINE-1). Outcome measures included the PSI, Psoriasis Area and Severity Index (PASI), static Physician's Global Assessment (sPGA), psoriasis-affected body surface area, 36-item Short-Form Health Survey version 2, and the Dermatology Life Quality Index (DLQI). The PSI was evaluated for dimensionality, item performance, reliability (internal consistency and test-retest), construct validity, ability to detect change, and agreement between PSI response and response measures based on the PASI, sPGA, and DLQI.

RESULTS

Results supported unidimensionality, good item fit, ordered responses, and PSI scoring. The PSI demonstrated reliability: baseline Cronbach's alpha ≥ 0.92 and intraclass correlation coefficients ≥ 0.95. Correlations between PSI total score and DLQI item 1 (r = 0.86), DLQI symptoms and feelings (r = 0.87), and 36-item Short-Form Health Survey version 2 bodily pain (r = -0.61) supported convergent validity. PSI scores differed significantly (P < 0.001) among severity groups based on the PASI (< 12/≥ 12), sPGA (0-1/2-3/4-5), body surface area (< 5%/5%-10%/> 10%), and DLQI (≤ 5/> 5) at weeks 8 and 12. At week 12, the PSI detected significant changes in severity based on PASI responses (< 50/50- < 75/≥ 75) and sPGA (0-1/≥ 2), and showed good agreement (k ≥ 0.66) between PSI response and PASI, sPGA, and DLQI responses.

CONCLUSION

The PSI demonstrated excellent validity, reliability, and ability to detect change in the severity of psoriasis signs and symptoms.