Reactivation of latent herpes simplex virus (HSV) type I or varicella-zoster virus (VZV) has been recognized as the most common pathomechanism underlying Bell's palsy. There is also increased reactivation of HSV or VZV in patients with immunosuppressed states and in cancer patients. The purpose of this study was to investigate the risk for cancer during a 5-year follow-up period after diagnosis of Bell's palsy by using a population-based dataset in Taiwan. We used data from the Longitudinal Health Insurance Database. We identified 2,618 patients with Bell's palsy as the study cohort and randomly selected 13,090 patients to be used as a comparison cohort. Cox proportional hazards regression was performed to compare the 5-year risk of subsequent cancer between the study and comparison cohorts. We found that the incidence of cancer was 1.55 (95 % CI 1.35-1.78) per 100 person-years for patients with Bell's palsy and 1.09 (95 % CI 1.02-1.18) per 100 person-years for comparison patients. After censoring cases that died from non-cancer causes during the follow-up period and adjusting for urbanization, monthly income, geographic region, and diabetes, the hazard ratio (HR) for cancer during the 5-year follow-up period for patients with Bell's palsy was 1.43 times that for comparison patients (95 % CI 1.22-1.73). There was a particularly increased risk of oral cancer (HR = 2.49; 95 % CI 1.54-4.03) for patients with Bell's palsy compared with the other patients. We conclude that patients with Bell's palsy were at significant risk of cancer during a 5-year follow-up period after diagnosis.
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