Measurement properties of a patient-reported outcome measure assessing psoriasis severity: The psoriasis symptoms and signs diary

J Dermatolog Treat. 2016 Aug;27(4):322-7. doi: 10.3109/09546634.2015.1114567. Epub 2015 Dec 4.

Abstract

Background: Collecting reliable and valid symptom information from patients is critical for assessing psoriasis severity in clinical research.

Objective: To evaluate measurement properties of a new patient-reported outcome (PRO), the Psoriasis Symptoms and Signs Diary (PSSD).

Methods: One hundred six US patients with moderate-to-severe plaque psoriasis completed two versions of the PSSD [a 24-hour recall (PSSD-24h) and 7-day recall (PSSD-7d)] using a 0-10 numerical rating scale. Reliability (test-retest and internal consistency), validity (convergent, divergent and known-groups), responsiveness, and version equivalence were evaluated. Minimally important difference was estimated.

Results: Based on exploratory factor analysis and clinical input, symptom, sign, and total severity scores were established. Internal consistency (Cronbach's alpha ≥ 0.944) and test-retest reliability (intraclass correlation coefficients ≥ 0.824) were acceptable. Correlations with Dermatology Life Quality Index (DLQI) (0.489 to 0.644) indicated convergent validity, while low correlations (< 0.30) with several Short Form (SF)-36 scales indicated divergent validity. PSSD scores differed when patients were categorized by Body Surface Area, DLQI, and Psoriasis Area Severity Index scores. PSSD-24h and PSSD-7d versions were equivalent (Pearson correlations ≥ 0.953).

Limitations: PSSD responsiveness should be evaluated in patients receiving treatment.

Conclusion: The PSSD is reliable and valid in measuring symptoms/signs of patients with moderate-to-severe plaque psoriasis.

Keywords: Psoriasis; assessment tool; minimal important difference; questionnaire; reliability; validity.

MeSH terms

  • Adult
  • Female
  • Humans
  • Male
  • Middle Aged
  • Patient Reported Outcome Measures*
  • Psoriasis* / drug therapy
  • Psychometrics / methods*
  • Quality of Life
  • Reproducibility of Results
  • Severity of Illness Index
  • Surveys and Questionnaires