Hyperhidrosis Quality of Life Index (HidroQoL©): further validation and clinical application in patients with axillary hyperhidrosis using data from a phase III RCT.

BACKGROUND The Hyperhidrosis Quality of Life Index (HidroQoL©) is a validated patient-reported outcome measure capturing the quality of life of people affected by hyperhidrosis. We aimed to extend the validity evidence to physician-confirmed diagnosis of primary axillary hyperhidrosis. METHODS Data from a phase 3 randomized placebo-controlled clinical trial were used (n = 171). Confirmatory factor analysis was carried out to confirm a priori two-factor structure of the HidroQoL. Internal consistency was assessed using Cronbach's alpha. Intraclass correlation coefficients (ICCs) were calculated to evaluate test-retest reliability after 4 to 7 days. Convergent validity was assessed using correlations with the Dermatology Life Quality Index (DLQI), the Hyperhidrosis Disease Severity Scale (HDSS) and gravimetric sweat production. Known groups were analyzed to evaluate discriminative validity. Responsiveness after 29 days was assessed and minimal important difference (MID) values were calculated using both anchor- and distribution-based approaches. All analyses were carried out for total HidroQoL and its two domains. RESULTS The two-factor structure of the HidroQoL could be confirmed. Internal consistency and test-retest reliability were strong (Cronbach's α: 0.81-0.90; ICCs: 0.89-0.93). Correlations with other outcome measures were in line with a priori hypotheses. The HidroQoL discriminated between different severity groups (p ≤ .001) and showed sensitivity to change towards improvement (p < .001). An MID value of 4 is proposed for the total scale. CONCLUSION This study supports excellent measurement properties including clinical applicability of the HidroQoL in primary axillary hyperhidrosis and suggests an MID of 4 to be applied to clinical trial data.