Development, validation and clinical application of a patient-reported outcome measure in hyperhidrosis : the Hyperhidrosis Quality of Life Index (HidroQoL ©)

Consideration of broader outcomes of disease, especially those exclusively experienced and reported by the patient, such as HRQOL, is not only consistent with the ‘whole person’ view of health contained in the 1948 WHO definition, but is also a prerequisite to building health-care systems that are responsive to the needs of the patients. For chronic skin diseases, such as hyperhidrosis, these provide a useful indicator of how a patient feels and functions disease for both practical and methodological reasons. The aims of this study therefore were to investigate the impact of hyperhidrosis on patients’ HRQoL using a mix of qualitative and quantitative methods. In addition, a further aim was to develop and validate a disease-specific instrument for assessing HRQoL in hyperhidrosis. In pursuing the above aims, the feasibility of applying online social networking sites for outcomes research in dermatology was assessed. Patients were recruited through online social networking communities related to hyperhidrosis for all stages of the study. Interviews, focus groups and surveys were used for collecting qualitative data from patients (n = 71) to understand quality of life issues of patients, and to provide the content of the new instrument. Dermatologists (n= 5) and patients (n=7) took part in the content validation of the HidroQoL©. Item reduction and the development of the scale’s structure was carried out through several field-testing studies (n: USA, 559; UK, 115), using the item response theory (IRT) Rasch model and factor analyses. Further psychometric testing was performed in a separate study (n = 241). Distribution-based methods were applied in establishing minimum clinically important difference (MCID). A thematic analysis of the qualitative data collected produced 29 quality of life themes and 102 sub-themes, forming the content for the initial 49-item HidroQoL©. The two expert panels judged the instrument as content valid, with a few suggestions. The Rasch analysis modelling led to the collapsing of response categories (from five to three) and the reduction in number of items (from 49 to 18), to ensure a perfect model fit. Factor analyses supported both a single- and a two-factor structure. In subsequent construct validation study the HidroQoL correlated with the DLQI (rs = 0.572, p < 0.01) and the Skindex-17 (rs = 0.551, p < 0.01). Reliability was high (Cronbach alpha = 0.9; test-retest ICC = 0.93). The scores were sensitive to change in patients’ disease severity (standard response mean = 0.8, 95% C.I: 0.34-1.27). The scale banding proposed for the HidroQoL score is as follows: 0 – 1, no effect at all; 2 – 11, small effect; 12 – 22, moderate effect; 23 – 32, large effect; 33 – 36, very large effect. The MCID values were 1.94 – 3.07, for generalised v hyperhidrosis, 2.16 – 4.36, for axillary hyperhidrosis, 2.15 – 3.39, for palmo-plantar hyperhidrosis. An MCID of three is currently being proposed for all types of hyperhidrosis. This study has provided the initial evidence supporting the appropriateness of the content of the HidroQoL and validity of inferences from its scores for assessing HRQoL in hyperhidrosis. In addition, the availability of MCID estimates for the HidroQoL will facilitate its clinical interpretation in both research and routine clinical practice. This study has also demonstrated how CTT and IRT can be integrated in the development and validation of a new generation of HRQoL instruments, using social network for patient recruitment.