The incidence and presumed aetiologies of fourth cranial nerve palsy in Korea: a 10-year nationwide cohort study

Aims To investigate the incidence and presumed aetiologies of fourth cranial nerve (CN4) palsy in Korea Methods Using the nationally representative dataset of the Korea National Health Insurance Service–National Sample Cohort from 2006 to 2015, newly developed CN4 palsy cases confirmed by a preceding disease-free period of ≥4 years were identified. The presumed aetiology of CN4 palsy was evaluated based on comorbidities around the CN4 palsy diagnosis. Results Among the 1,108,292 cohort subjects, CN4 palsy newly developed in 390 patients during 10-year follow-up, and the overall incidence of CN4 palsy was 3.74 per 100,000 person-years (95% confidence interval, 3.38–4.12). The incidence of CN4 palsy showed a male preponderance in nearly all age groups, and the overall male-to-female ratio was 2.30. A bimodality by age-group was observed, with two peaks at 0–4 years and at 75–79 years. The most common presumed aetiologies were vascular (51.3%), congenital (20.0%), and idiopathic (18.5%). The incidence rate of a first peak for 0–4 years of age was 6.17 per 100,000 person-years, and cases in this group were congenital. The second peak incidence rate for 75–79 years of age was 11.81 per 100,000 person-years, and the main cause was vascular disease. Strabismus surgery was performed in 48 (12.3%) patients, most of whom (72.9%) were younger than 20 years. Conclusion The incidence of CN4 palsy has a male predominance in Koreans and shows bimodal peaks by age. The aetiology of CN4 palsy varies according to age-groups.