Increased risk of ischemic stroke in patients with Bell's palsy: A longitudinal follow-up study using a national sample cohort

To investigate the association between Bell's palsy and stroke according to the different types of stroke, using a sample cohort based on the national Korean population. Individuals aged ≥ 20 years were collected from the Korean National Health Insurance Service National Sample Cohort between 2002 and 2013. We extracted the data for Bell's palsy patients (n = 3658) and 1:4 matched controls (n = 14,632) and analyzed the occurrence of hemorrhagic or ischemic stroke in both groups. Matching was performed on the basis of age, gender, income, and region of residence. For Bell's palsy, we included only participants who received the diagnosis (ICD-10 code, G510) 2 or more times via ambulatory visits for the same episode with steroid treatment. Patient admission histories were used to identify occurrences of hemorrhagic stroke (I60, I61 and I62) and ischemic stroke (I63). Adjusted hazard ratios were calculated using stratified Cox proportional hazard models for the Charlson comorbidity index and 95% confidence intervals (CIs). For the subgroup analyses, we divided the participants by age, sex, and each time period after the onset of Bell's palsy (≤1 year, 1 to 2 years, 2 to 3years, > 3years). The risk of ischemic stroke was significantly increased in Bell's palsy patients compared to that in the controls (adjusted HR = 1.74, 95% CI = 1.38–2.19, P < 0.001). In the subgroup analyses, a significant association between two clinical disorders was observed in patients aged ≥ 50 years old, regardless of gender. The risk of ischemic stroke was significantly increased, especially within 2 years after Bell's palsy. In contrast, the risk of hemorrhagic stroke was not significantly increased. There is an association of Bell's palsy with ischemic stroke but not with hemorrhagic stroke.