In general, patients presenting with immediate-onset complete facial paralysis are most likely to need surgery. Some authors argue that ENoG should be the primary method of determining which patients should be explored because it is more objective than historic information.5,6 Nosan et al5 found that all patients presenting with temporal bone trauma with facial paralysis who demonstrated ENoG >190% degeneration had significant facial nerve pathology at time of exploration, regardless of time of onset of paralysis.
Fisch7 demonstrated the utility of ENoG in assessing facial nerve function and prognosticating likelihood of recovery. He noted that patients who had undergone deliberate facial nerve transection for tumors resulted in 100% degeneration on ENoG in 3 to 5 days. Fisch also presented three patients with delayed facial paralysis occurring 3 to 7 days after vestibular nerve section. ENoG showed progressive denervation that became complete after 14 to 21 days, and all three patients had nearly complete return of facial function. Therefore, if ENoG demonstrates > /90% degeneration in the first 6 days, one can infer that significant facial nerve injury has occurred and surgical exploration should be carried out. On the other hand, if >190% degeneration does not occur until 14 days, then good recovery is expected without surgical intervention.
The group of patients who obtain > /90 to 95% degeneration between 6 and 14 days have various degrees of intermediate nerve injury. Facial nerve exploration in these patients can benefit those few who would otherwise have poor spontaneous recovery. Patients who present several months after the initial injury can be followed with electromyography (EMG) to detect subclinical return of facial nerve function. If no return of function is detected within 6 to 12 months, facial nerve exploration is warranted. Delayed exploration should be performed within 1 year, as nerve-grafting results tend to deteriorate after this interval.
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