Incremental Prognostic Value of Electrodiagnostic Results Beyond House-Brackmann Grade in Bell Palsy

Importance Current guidelines recommend electrodiagnostic testing in Bell palsy primarily for patients with complete or near-complete facial paralysis (House-Brackmann [H-B] grade V-VI). It is unclear whether patients with moderate paralysis (H-B grade IV) would benefit from this testing. Objective To quantify the incremental prognostic value of electrodiagnostic findings beyond initial H-B grade for 6-month recovery from Bell palsy, including in moderate paralysis. Design, Setting, and Participants This single-center cohort study included adults with acute Bell palsy between January 2010 and December 2025 who underwent standardized 4-branch electroneuronography and needle electromyography approximately 14 days after onset. Patients with Ramsay Hunt syndrome, bilateral palsy, or incomplete corticosteroid treatment were excluded. Exposures An electroneuronography degeneration index (ENoG DI) of 90% or greater in any facial muscle branch, complete denervation (no voluntary motor unit activity on needle electromyography), and co-occurrence in the same muscle. Main Outcomes and Measures Incomplete recovery at 6 months was defined as final H-B grade II or higher. Adjusted odds ratios (AORs) were estimated using Firth penalized logistic regression, overall and stratified by initial H-B grade. Incremental prognostic value was assessed by change in area under the receiver operating characteristic curve (ΔAUROC). Results Of 3506 patients (mean [SD] age, 50.8 [17.0] years; 1878 [53.6%] female), 1891 (53.9%) completed 6-month follow-up; 1040 (55.0%) had incomplete recovery. Overall, ENoG DI of 90% or greater in any branch (AOR, 4.96; 95% CI, 3.97-6.19) and complete denervation (AOR, 5.91; 95% CI, 4.06-8.60) were independently associated with incomplete recovery; in initial H-B grade IV, both remained associated (AOR, 3.19; 95% CI, 2.00-5.11 and AOR, 3.17; 95% CI, 1.03-9.78, respectively). Co-occurrence of both findings had the highest odds of incomplete recovery in all patients (AOR, 8.41; 95% CI, 5.46-12.95) and in patients with initial H-B grade IV (AOR, 3.10; 95% CI, 1.01-9.54). Adding ENoG DI findings to initial H-B grade improved model discrimination (AUROC, 0.78 [95% CI, 0.76-0.80] vs 0.72 [95% CI, 0.70-0.74]; ΔAUROC, 0.06; 95% CI, 0.04-0.07). Conclusions and Relevance In this cohort study, ENoG DI of 90% or greater and complete denervation were independently associated with incomplete recovery even in moderate paralysis. These findings suggest that electrodiagnostic results may refine prognostic assessment in selected patients with moderate paralysis and warrant prospective validation before broader clinical application.