Objective: To determine the nationwide prevalence and incidence rates of primary dystonia in Wales.

Background: The true prevalence and incidence of dystonia remains largely unknown and varies widely across distinct studies. Current estimates are based on small numbers limited to discrete geographical locations. Accurate epidemiological information is vital, not only for improved understanding of the disorder, but also to ensure better provisioning of clinical services and to provide context for diagnostic decision-making.

Method: We have reviewed anonymised, electronic healthcare records in the Secure Anonymised Information Linkage (SAIL) Databank of more than 3.6 million individuals in Wales to ascertain primary dystonia cases between 1^st January 1994 and 31^st December 2017. A reference population of 82 patients with a clinically confirmed dystonia diagnosis were linked to records contained within SAIL and used to construct a diagnostic algorithm. Using International Classification of Diseases (ICD-version 10) and Read codes, cases of primary dystonia were identified within hospital and general practice records, while excluding those with potential secondary causes. Prevalence and incidence rates were calculated, and therapeutic intervention, deprivation scores and mortality records were also obtained.

Results: Our diagnostic algorithm achieved a sensitivity of 82%, enabling us to identify a total of 57,204 individuals within the SAIL databank as having been diagnosed with primary dystonia. The prevalence of primary dystonia was 1.5% amongst the Welsh population. Incidence rate was 1/1000 person-years throughout the study period. More than half of the cases (56%) had a first diagnosis of cervical dystonia, while Myoclonus Dystonia was the least common subtype (0.02%). Overall, there was a female preponderance (1:1.5, male:female), with females out numbering males in all subtypes expect Myoclonus Dystonia. The median age at first diagnosis was 37 years, with 63.3% of cases presenting with the adult-onset (≥26 years) form.

Conclusion: We conclude that prevalence was higher than that recorded in previous studies, this may in part be explained by the extensive coverage of individuals within the SAIL databank. These findings have important implications for healthcare professionals given the comorbidities associated with dystonia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-national-data-linkage-study-of-incidence-and-prevalence-of-primary-dystonia/