Variation Found in Patient-Reported Outcome Measures for Pruritus

The overall quality of evidence for patient-reported outcome measures for pruritus differs considerably and no measure performed particularly well, according to study findings published in the Journal of Investigative Dermatology.

Researchers conducted a Medline search regarding the measurement properties of patient-reported outcome measures for pruritus to update the systematic review published in 2017 and to identify new validation studies published from October 2015 to July 2019.

The methodological quality of validation studies was assessed with use of the COnsensus-based Standards for the selection of health status Measurement INstruments (COSMIN) checklist, and the measurement properties of patient-reported outcome measures were evaluated.

A total of 19 new studies were identified in addition to the 22 studies that were included in the previous review. Sample sizes in the new studies ranged from 40 to 3641 participants. In combination with the original review, 38 different outcome measures were identified, of which 20 were grouped in the category pruritus intensity, 10 to pruritus severity, 3 to pruritus-specific health-related quality of life (HRQoL), and 5 to others.

Retest reliability and construct validity (hypotheses testing) were the most frequently assessed criteria. Criterion validity and measurement error were not addressed in any study.

Overall, the evidence for the quality of outcome measures differed considerably, and no measure formally performed especially well, according to the study authors. Methodological quality did not reach an “excellent” level in any study and was mostly rated as fair only.

The researchers identified 20 outcome measures for pruritus intensity and were not able to recommend 1 particular measure. Of these measures, 11 scales were not eligible for recommendation, mostly because of unknown or limited evidence for particular measurement properties, and 9 had unknown or limited evidence levels for all considered criteria.

A total of 10 measures assessed pruritus severity. The Itch Severity Scale (ISS) showed adequate internal consistency, responsiveness, and convergent and divergent validity, based on a moderate evidence level, according to the researchers.

For measuring pruritus-specific HRQoL, the Itchy Quality of Life and the Uremic Pruritus in Dialysis Scale had the most promising results, according to the study authors.

The investigators noted some limitations to their findings, which are based on a systematic search in the Medline library only. Also, study populations differed considerably in some cases, and the COSMIN checklist from 2010 was used instead of the updated version published in 2018.

“Results of this systematic review on [measurement properties] can support decisions of researchers and clinicians on which instrument to choose for their research purpose or clinical consultation,” stated the researchers. “With regard to the decision on an outcome measure, it needs to be emphasized that aggregated ratings for single outcome measures did not exceed a moderate evidence level. Future validation studies should therefore focus on rigorous methodological quality and thorough reporting of methodology so that statements on measurement properties will be based on a strong evidence level.”

Disclosure: Some of the study authors declared affiliations with pharmaceutical companies. Please see the original reference for a full list of authors’ disclosures.

Reference

Topp J, Apfelbacher C, Ständer S, Augustin M, Blome C. Measurement properties of patient-reported outcome measures for pruritus: an updated systematic review. J Invest Dermatol. Published online July 30, 2021. doi:10.1016/j.jid.2021.06.032