Impact of Age and Nerve Impairment Interaction on Bell's Palsy Prognosis

OBJECTIVES: Age as a prognostic factor for Bell's palsy remains debated. This study aimed to assess prognosis in older adults and clarify whether the interaction between aging and nerve-impairment severity, evaluated by the Nerve Excitability Test (NET), affects recovery. METHODS: This retrospective cohort study included 181 patients diagnosed with idiopathic peripheral facial nerve palsy (Bell's palsy) at Ehime University between 2011 and 2020 (older group, ≥ 65 years: 57; non-older group, < 65 years: 124). In multivariate logistic regression, factors associated with incomplete recovery were assessed, including age, sex, comorbidities, NET results (abnormal or difference ≥ 3.5 mA), and the age-by-NET interaction. RESULTS: Diabetes mellitus (29.8% vs. 15.3%, p = 0.03) and hypertension (36.8% vs. 10.5%, p < 0.01) were significantly more prevalent in the older group; nonetheless, abnormal NET rates did not differ between groups (47.4% vs. 44.4%). In multivariate analysis, after adjusting for other factors, only abnormal NET results were independently associated with poor prognosis (odds ratio [OR] 2.31, 95% CI: 1.11-4.79, p = 0.02). Notably, the age-by-NET interaction term was significant (OR 10.7, 95% CI: 1.79-64.30, p = 0.01), indicating significantly poorer recovery in older adults with severe nerve impairment than in younger patients. CONCLUSION: Severe nerve degeneration strongly predicts poor prognosis in older adults with Bell's palsy. Because of reduced nerve regeneration capacity and axonal reserve, recovery from severe nerve injury is challenging; therefore, early, aggressive intervention is necessary.