The development and validation of a disease-specific quality of life measure in hyperhidrosis: the Hyperhidrosis Quality of Life Index (HidroQOL©)

Abstract

Purpose: To develop and validate a new disease-specific quality of life measure in hyperhidrosis for use in both routine clinical practice and clinical research.

Methods: Interviews and focus group discussions with hyperhidrosis patients, reported elsewhere, provided the content for the measure validated in this study (n = 71). A panel of dermatologists (n = 5) and patients (n = 7) carried out content validation. Further, item reduction and the initial construct validation were carried out in a cross-sectional study (n = 595), using the unidimensional Rasch analysis and exploratory factor analysis. Subsequently, the construct validity, reliability and responsiveness of the revised measure were assessed in a longitudinal study (n = 260). Data collection for the item reduction and the final validation phases was entirely carried out online.

Results: The expert panels judged the HidroQoL as content valid. Rasch analysis supported the revision of response options from five to three. Following removal of misfitting items, a set of 15 items showed optimal fit to the model (chi-squared statistic = 159.64, p = 0.07). Three additional items were retained on consideration of their importance to patients, resulting in an 18-item instrument. The items were grouped into two subscales, daily life activities and psychosocial life domains, based on results of the factor analysis. In subsequent construct validation, the HidroQoL correlated with the DLQI (r s = 0.6, p < 0.01). Reliability was high (internal consistency, Cronbach's alpha: overall scale = 0.9; test-retest reliability, Intra-class correlation = 0.9). The HidroQoL scores were sensitive to change in patients' disease severity (score change from baseline to follow-up after 15-35 days, Cohen's ES = 0.47).

Conclusion: This study has provided the initial evidence supporting measurement properties and the use of the HidroQoL instrument in both routine clinical practice and in research, for assessing quality of life impacts in hyperhidrosis.

Fig. 1

Disordered category thresholds for the item I avoid public speaking. Category threshold for scores 0–1 is on a higher location (QoL impairment) than for scores 1–2. Scores 1 (= a little) and 3 (= quite a bit) have no range on the latent QoL variable over which they are most likely

Fig. 2

Appropriately ordered category thresholds for the item I avoid public speaking after rescoring. Following rescoring from a 5 to a 3 point scale, the category thresholds 0–1 and 1–2 are monotonically ordered. Each score has a range on the latent QoL variable (location) over which it is the most likely

Fig. 3

The final version of the HidroQoL© with 18 items. The new hyperhidrosis-specific QoL instrument, the Hyperhidrosis Quality of Life Index