Prevalence of infratentorial superficial siderosis in a large general population sample from the UK Biobank.

Background: Classical infratentorial superficial siderosis (iSS) is considered a rare but potentially disabling neurological disorder. It results from slow chronic blood extravasation into the cerebrospinal fluid and deposition of the iron degradation product hemosiderin within the subpial layers of the central nervous system. Susceptibility-weighted (SW) magnetic resonance imaging (MRI) is the reference diagnostic modality. Few studies have described the population prevalence of cerebellar or infratentorial siderosis, and there are none from the UK population. The aim of this cross-sectional observational study was to estimate the prevalence of iSS in the UK Biobank sample using pre-defined radiological criteria.

Methods: We reviewed SW MRIs of participants from the UK Biobank, looking for the radiological features of classical iSS: involvement of infratentorial structures (superior vermis, cerebellar folia, brainstem, or craniocervical junction). We calculated the point prevalence as the number of identified cases per total number of cases reviewed and 95% confidence intervals (CI) using Wilson's Score formula.

Results: Of 10,305 SW MRIs reviewed, five cases with radiological features of iSS were identified demonstrating cerebellar/superior vermis involvement. The estimated prevalence of iSS was calculated as 48.5 (95%CI 20.7-113.5) cases per 100,000 population.

Conclusions: This is the first study to estimate iSS prevalence in the UK population. The prevalence of iSS is higher than that reported for other rare neurological and neuro-otological disorders, suggesting an important unmet healthcare need for early diagnosis and targeted management strategies. Further studies are needed to determine the clinical associations and prognostic significance of radiologically defined iSS in the general population.