Cost-of-illness studies in rare diseases: a scoping review

OBJECTIVE: The aim of this scoping review was to overview the cost-of-illness studies conducted in rare diseases. METHODS: We searched papers published in English in PubMed from January 2007 to December 2018. We selected cost-of-illness studies on rare diseases defined as those with prevalence lower than 5 per 10,000 cases. Studies were selected by one researcher and verified by a second researcher. Methodological characteristics were extracted to develop a narrative synthesis. RESULTS: We included 63 cost-of-illness studies on 42 rare diseases conducted in 25 countries, and 9 systematic reviews. Most studies (94%) adopted a prevalence-based estimation, where the predominant design was cross-sectional with a bottom-up approach. Only four studies adopted an incidence-based estimation. Most studies used questionnaires to patients or caregivers to collect resource utilisation data (67%) although an important number of studies used databases or registries as a source of data (48%). Costs of lost productivity, non-medical costs and informal care costs were included in 68%, 60% and 43% of studies, respectively. CONCLUSION: This review found a paucity of cost-of-illness studies in rare diseases. However, the analysis shows that the cost-of-illness studies of rare diseases are feasible, although the main issue is the lack of primary and/or aggregated data that often prevents a reliable estimation of the economic burden.