Prognostic value of electrodiagnostic tests in complete Bell's palsy

Prediction of the course or outcome of Bell's palsy based on clinical findings is disappointing. Electrodiagnostic studies are useful in establishing prognosis, but for most of them this is possible only very late after onset of the illness. A survey of 92 patients with complete Bell's palsy seen during the past 10 years, and a statistical evaluation of the electrodiagnostic tests, are presented. The tests included conduction time, minimal excitability ratio and difference, electroneuronography and needle electromyography (EMG). The combination of all these tests enabled us to predict recovery during the first few weeks after onset of the disease. Evidence for conduction block during the first three weeks is without prognostic significance, while later on it is indicative of a poor prognosis (p<0.01). There was a significant correlation between persistence of neurological deficit and increased minimal stimulation ratio and difference. Evidence of extensive, profuse fibrillation potentials is indicative of a good prognosis after the first three weeks, while the appearance of such potentials early after the onset is not significantly correlated with the prognosis. The EMG pattern of recruitment and its amplitude is significantly correlated with clinical recovery from the beginning of the palsy. The main prognostic distinction depends on identification of the degree of axonal degeneration. The decreased amplitude of the evoked response is proportional to the extent of axonal loss. Preservation of evoked response amplitude of less than 10% of that of the normal side is associated with a poor prognosis. We conclude that electroneuronography has the best predictive value (r=0.83).