Adult‐onset idiopathic dystonia: A national data‐linkage study to determine epidemiological, social deprivation, and mortality characteristics

BACKGROUND AND PURPOSE: Accurate epidemiological information is essential for the improved understanding of dystonia syndromes, as well as better provisioning of clinical services and providing context for diagnostic decision‐making. Here, we determine epidemiological, social deprivation, and mortality characteristics of adult‐onset idiopathic dystonia in the Welsh population. METHODS: A retrospective population‐based cohort study using anonymized electronic health care data in Wales was conducted to identify individuals with dystonia between 1 January 1994 and 31 December 2017. We developed a case‐ascertainment algorithm to determine dystonia incidence and prevalence, as well as characterization of the dystonia cohort, based on social deprivation and mortality. RESULTS: The case‐ascertainment algorithm (79% sensitivity) identified 54,966 cases; of these cases, 41,660 had adult‐onset idiopathic dystonia (≥20 years). Amongst the adult‐onset form, the median age at diagnosis was 41 years, with males significantly older at time of diagnosis compared to females. Prevalence rates ranged from 0.02% in 1994 to 1.2% in 2017. The average annual incidence was 87.7/100,000/year, increasing from 49.9/100,000/year (1994) to 96.21/100,000/year (2017). In 2017, people with dystonia had a similar life expectancy to the Welsh population. CONCLUSIONS: We have developed a case‐ascertainment algorithm, supported by the introduction of a neurologist‐reviewed validation cohort, providing a platform for future population‐based dystonia studies. We have established robust population‐level prevalence and incidence values for adult‐onset idiopathic forms of dystonia, with this reflecting increasing clinical recognition and identification of causal genes. Underlying causes of death mirrored those of the general population, including circulatory disorders, respiratory disorders, cancers, and dementia.