Bell’s palsy is an acute idiopathic paresis or paralysis of the peripheral facial nerve. It is the most common cause of facial nerve palsy with a reported incidence ranging from 11.5–55.3 per 100,000. The aetiology remains unclear. Several studies have reported that the number of patients with Bell’s palsy was significantly different among months and seasons, with a trend of higher incidence in winter. The authors performed a retrospective study using data from the National Health Insurance Service of Korea from 2008 to 2020. All Korean people are obligated to join this service and so data is felt to be based on the entire population. They identified 969,312 patients with Bell’s palsy attending medical or traditional medical services. The total average monthly incidence differed significantly by month, the highest observed in January (9.1 per 100,000) and the lowest in June (7.7 per 100,000) (p < 0.001). This was also seen, in regard to sex, age and residence (highest incidence in January and lowest in June). In discussion, the authors suggest further the rationale for the study with suggestion of controversy about monthly / seasonal variation of Bell’s palsy, quoting a Danish and UK study (Peitersen et al and Rowlands et al respectively) who had shown no difference in incidence for season in 1701 and 2473 patients respectively. They go on to describe other study areas (USA, Greece, Taiwan, South Africa) that have seen a seasonal trend. The authors suggest the rationale for seasonal variation, with the winter being worse, may be related to environmental and meteorological factors associated with winter, with suggestion of reactivation of herpes simplex virus, increased susceptibility to upper respiratory tract infections, increased blood viscosity, cold exposure neuritis, and seasonal affective disorder as potential causes at these times of year. The authors have highlighted the limitations of the study – its retrospective nature and potential coding errors in data collection. I think the data can be useful for the UK, given some climate similarities (four distinct seasons) and it is useful to see the sheer volume of cases to allow for statistical power.
Bell’s palsy incidence in Korean population
Reviewed by Aaron Ferguson
Monthly Variation in Bell’s Palsy Based on Population Data of Korea.
