The Family Dermatology Life Quality Index: measuring the secondary impact of skin disease

Background Skin diseases are known to have a major impact on the lives of patients and their families. Many instruments are available to measure the health-related quality of life (HRQoL) of patients but no measure has been developed so far to quantify the secondary impact on family members of the patients. Objectives To develop and validate a dermatology-specific instrument to measure the adverse impact on the HRQoL of family members of patients with skin disease. Methods Detailed semi-structured interviews were conducted with family members of patients to identify different aspects of HRQoL affected. An initial draft version of the questionnaire based on the main topic areas was pilot tested to assess the face and content validity. A 10-item questionnaire, the Family Dermatology Life Quality Index (FDLQI), was finalized after modifications to the draft questionnaire based on feedback from families and dermatology professionals and on item reduction. Psychometric evaluation was conducted on a new cohort of family members (n = 132) who completed the FDLQI and the patients (n = 109) who completed the Dermatology Life Quality Index (DLQI). Results Fifty-nine different aspects of family members' HRQoL were identified from the analysis of the interviews, which were categorized into main topic areas. Factor analysis of 10 items of the final questionnaire revealed two factors and together these explained 60% of the common variance. The FDLQI demonstrated high internal consistency (Cronbach's alpha = 0.88) and test-retest (intraclass correlation coefficient = 0.94) reliabilities. The responsiveness of the instrument to change was shown by significant change in the family members' FDLQI scores in cases where patients' clinical condition either improved or worsened. Construct validity was assessed by testing a number of a priori hypotheses. A strong correlation was seen between the family members' FDLQI scores and patients' DLQI scores (r = 0.69), a significantly higher FDLQI score was seen for inflammatory skin diseases compared with noninflammatory diseases/isolated lesions (P < 0.0001), and there was a positive relationship between the family members' FDLQI scores and patients' disease severity (r = 0.49). Conclusions The FDLQI is simple and practical and seems to have the potential to be used as an additional outcome measure in clinical practice and evaluation research.