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

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.

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.

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.

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.