Recovery from acute Bell's palsy (BP) is variable and there are few predictors of response. We evaluated the usefulness of a range of neurophysiological parameters to predict outcome in BP.

Fifty-nine patients (age: 33.7±15.4 years) with acute unilateral BP were recruited within 3–7 days of onset. They were evaluated with electroneurography, facial nerve excitability, and the blink reflex. House-Brackmann (HB) clinical scores were obtained at the same time and three months later. All patients received prednisolone treatment and regular rehabilitation.

At three months, 41 patients (69.5%) had good recovery, while 18 patients (30.5%) had poor recovery according to the HB scale. The facial nerve excitability threshold and threshold difference between sides were significantly lower in patients with good recovery than those with poor recovery (P values=0.022 and 0.006 respectively). Facial nerve degeneration rate (1 – affected/unaffected amplitude of CMAP of muscle ×100%) recorded in frontalis (P=0.002) and orbicularis oris (P=0.038) were also smaller in good recovery than poor recovery patients. There were no differences in latency and amplitude of CMAPs recorded from frontalis or orbicularis oris muscle, nor in latencies of the components of the blink reflex. ROC analysis showed that patients who had a threshold side difference <13mA (35 cases), had a higher chance of good recovery (85.7% versus 14.3% poor recovery). Patients who had a degeneration rate<50% (38 cases) also had a higher chance of good recovery (78.9%) versus 21.1% who had poor recovery, while patients with a degeneration rate>50% (21 cases) had a 47.8% chance of good recovery versus 52.2% poor recovery (P=0.004). Logistic regression analysis showed that the most significant predictive indicator of BP recovery was the facial nerve degeneration rate of frontalis muscle (P=0.011).

Facial nerve degeneration rate of frontalis muscle provides the most sensitive prognostic indicator of recovery from acute BP and may provide useful management strategies.