Monthly Variation in Bell's Palsy Based on Population Data of Korea

Introduction: Several studies have reported that the number of patients with Bell's palsy varied significantly by month and season. However, few studies have reported the monthly variation in Bell's palsy based on the whole population. We investigated the monthly variation in Bell's palsy in Korea during a long-term period based on whole population data. Methods: This retrospective study used the data of the National Health Insurance Service of Korea, which included the entire Korean population from 2008 to 2020. The monthly incidence of Bell's palsy per 100,000 was evaluated in total and according to sex, age, and residence. Results: The total average monthly incidence differed significantly by month, with the highest observed in January (9.1 per 100,000) and the lowest in June (7.7 per 100,000) (p < 0.001). The average monthly incidence according to sex, age, and residence also varied significantly by month, with most of the highest values noted in January and the lowest in June. Conclusion: There was significant monthly variation in the incidence of Bell's palsy, with the highest in January during the winter and the lowest in June during the summer, based on whole population data over a long-term period in Korea.