Itch Severity Scale: a self-report instrument for the measurement of pruritus severity

Background Assessing pruritus severity is difficult because of its subjective nature. A questionnaire that takes into account how the symptom is perceived by the patient may provide a more accurate representation of the pruritus. However, recently developed questionnaires do not specifically quantify severity of the symptom. Objectives To develop a self‐report questionnaire to measure pruritus severity and to provide initial evidence of its validity and reliability. Methods We modified a previously developed interview for the characterization and evaluation of pruritus, which was completed along with the RAND‐36 Health Status Inventory and Dermatology Life Quality Index by patients with psoriasis‐associated pruritus. Exploratory factor analysis, studies of internal consistency, and correlation analyses with health‐related quality of life scores were used to help determine which components of the modified pruritus interview to include in the new questionnaire, the Itch Severity Scale (ISS). The ISS was then assessed for construct validity, internal consistency reliability and test–retest reliability. Results Seven of the initial 11 components of the modified pruritus interview were included in the ISS. ISS scores correlated moderately with physical (r = −0·483) and mental (r = −0·492) health composite scores of the RAND‐36 and strongly with Dermatology Life Quality Index scores (r = 0·628), evidence of construct validity. It had an internal consistency reliability of 0·80 and a test–retest reliability of 0·95. Conclusions Based on this preliminary evidence of validity and reliability, this new seven‐item ISS may be useful in comparing pruritus severity among different disease populations or in assessing pruritus treatment effectiveness.