Development and evaluation of a personalised psychological intervention to improve adherence to photoprotection in adults with Xeroderma Pigmentosum (XP)

Background: Poor adherence to photoprotection from ultraviolet radiation in the rare disease xeroderma pigmentosum can be life-threatening due to heightened risk of skin cancers. This novel, two-phase research programme used mixed methods to investigate photoprotection in xeroderma pigmentosum, and its psychosocial impact, to develop an intervention to improve photoprotection. Objective(s): Phase I: To identify barriers to optimal photoprotection. Phase II: To design and test a personalised psychological intervention to improve photoprotection. Design: Phase I: Interview study; n-of-1 photoprotection study; objective measurement of ultraviolet radiation exposure study; international cross-sectional survey. Phase II: Consensus conference to synthesise findings and determine targets/priorities for intervention; intervention development using Intervention mapping; randomised controlled trial to test efficacy, costeffectiveness and intervention mechanisms. Settings for Phases I and II: National Xeroderma Pigmentosum Service, Guy’s and St Thomas’ NHS Foundation Trust, London, United Kingdom; Specialist xeroderma pigmentosum clinics in Regensburg, Germany, Japan, Tunisia; Patient support organisations in France and USA. Participants: Children < 16 (Phase I only) and adults (> 16) diagnosed with xeroderma pigmentosum. Intervention (Phase II): XPAND is a seven-session personalised psychological intervention designed to be facilitated by non-psychologists, delivered in spring to summer 2018 versus wait list control (intervention in spring to summer 2019). Main trial outcome measure (Phase II): Average daily ultraviolet radiation dose to the face calculated by combining objective ultraviolet radiation exposure with self-reported photoprotection. Results: Phase I: Varying levels of photoprotection were found, with most participants doing less than clinically recommended. The international survey (N = 156) and estimation of ultraviolet radiation dose-to-face (N = 41) found that adults had worse photoprotection than the ‘cared for’ sample, but that overall the total dose-to-face was similar in the two groups because the ‘cared for’ group were outside more. The n-of-1 study (N = 20) showed that fluctuations in protection were associated with time of day, weekday versus weekend, environmental risk perceptions and symptoms resulting from exposure, self-regulatory and psychological constructs. The qualitative study (N = 25) identified three modes of adaptation to photoprotection: (1) ‘dominated’, (2)‘integrated’ and (3) ‘resistant’. Modifiable drivers of photoprotection behaviour were identified in the survey studies, including belief-based predictors and the important role of habits. These combined findings informed the development and targets of the XPAND intervention. Phase II: The intervention group (n = 6) had significantly lower daily average ultraviolet radiation dose-to-face (primary outcome) compared to control (n = 7) (−0.25 Standard Erythemal Dose, p < 0.001, Hedge’s g = 2.2). Health economic analysis indicated that the intervention was associated with lower costs than control (£2642, 95% confidence interval −£8715 to £3873) and fewer qualityadjusted life-years (−0.0141, 95% confidence interval −0.0369 to 0.0028). Interviews found that XPAND was acceptable, and that greater automaticity and confidence contributed to improvements in photoprotection. Limitations: Due to the low prevalence of xeroderma pigmentosum, piloting was not possible and participant numbers in the trial were small, and some analyses were underpowered. The randomisation resulted in an imbalance in between-group baseline measures of ultraviolet radiation protection, and there was a lack of participant blinding. The magnitude, duration, cost-effectiveness and generalisability of the intervention are difficult to evaluate. The small sample size means we have to be cautious about both costs and QALYs, and in the short term we probably would not expect QALY differences given the long-term aims of photoprotection. Conclusions: Phases I and II: Determinants of inadequate photoprotection in xeroderma pigmentosum were identified and successfully targeted in a comprehensive and personalised intervention, which was acceptable to patients. The reduction in daily ultraviolet radiation dose to the face was larger than the clinically agreed difference anticipated to be effective in reducing the number of skin cancers in xeroderma pigmentosum. XPAND was associated with lower costs, below the incremental cost-effectiveness threshold of £20,000 on a cost-effectiveness plane, due to less service use, and quality-adjusted life-years were similar, although cost-effectiveness results did not reach statistical significance. Rare disease research is challenging; the success of XPAND shows that scientific rigour is possible and intervention efforts worthwhile.