Electroneurographic Degeneration Index Before Facial Rehabilitation in Idiopathic Facial Palsy (Bell's Palsy): A Prospective Observational Cohort of 90 Patients

Abstract

Background: Early oral corticosteroids, with or without antivirals, are the established first-line treatment for idiopathic facial palsy (IFP, Bell's palsy), and most patients recover. Clinical grading in the acute phase, however, cannot distinguish a conduction block from axonal degeneration, and rehabilitation is usually started without objective information about the state of the nerve. Electroneurography (ENoG) quantifies the proportion of degenerated motor axons as a degeneration index (DI). Objective: To describe how the pre-rehabilitation ENoG DI relates to clinical severity, and to describe recovery trajectories by DI stratum, in patients with IFP managed with medical therapy plus adjunctive, DI-informed rehabilitation. Materials and Methods: his prospective, single-centre, single-arm observational cohort study included 92 patients with acute IFP. Baseline ENoG was performed within 10 days of symptom onset (median: 6 days). The DI was calculated for five facial muscles representing the major peripheral branches of the facial nerve using the formula: DI (%) = 100 − [(CMAP amplitude on the affected side / CMAP amplitude on the unaffected side) × 100]. House–Brackmann (HB) grade and the Sunnybrook Facial Grading System (SBFGS) score were assessed by an independent physiotherapist at baseline and on Days 21 and 42 after baseline. All patients received oral corticosteroids; 40% initiated treatment within 72 hours of symptom onset and 60% thereafter. All patients received a structured facial rehabilitation programme, including facial exercises, massage and therapeutic ultrasound. Low-level laser therapy and extracorporeal shockwave therapy were allocated according to predefined DI strata: mild (<25%), moderate (25%–50%) and severe (>50%). Outcomes were compared across these strata. Results: The mean age was 35.4 ± 14.8 years, and 62 of 90 patients with recorded sex were men. Mean baseline DI was approximately threefold higher in the severe stratum than in the mild stratum (60.2% ± 10.3% vs. 19.4% ± 5.4%). The corresponding mean HB grades differed by less than one grade (3.69 vs. 2.78; p = 0.001). Across the cohort, DI, HB grade and SBFGS scores improved by Day 42 (all p < 0.001). Among the 90 patients included in the complete repeated-ENoG analysis, 81 (90.0%) achieved HB grade I by Day 42. The proportion of baseline DI resolved was similar across the mild, moderate and severe strata (80.5%, 83.3% and 83.9%, respectively; p = 0.87). However, Day-42 SBFGS scores remained lower in the severe stratum than in the mild stratum (93.2 vs. 97.3; p = 0.003). The proportion achieving HB grade I showed a non-significant downward trend across the strata (94.4%, 90.2% and 84.4%, respectively; p = 0.52). Higher baseline DI was associated with a greater number of rehabilitation sessions (mean: 22.0, 29.7 and 32.4 in the mild, moderate and severe strata, respectively; p = 0.002; Spearman’s ρ = 0.35, p < 0.001). Conclusion: Pre-rehabilitation ENoG DI provided objective information about the extent of nerve injury that was not fully captured by clinical grading. Higher baseline DI was associated with greater residual facial dysfunction at six weeks and a greater number of rehabilitation sessions. Recovery was frequent during follow-up under the combined medical and rehabilitation pathway. However, the absence of a control group and the potential contribution of spontaneous recovery preclude attributing these outcomes to rehabilitation or DI-based treatment allocation. Controlled studies are needed to determine whether DI-guided rehabilitation improves outcomes compared with standard rehabilitation.