It is taught that a complete facial nerve (FN) palsy after temporal bone (TB) trauma should be conservatively managed if electroneuronography (ENoG) shows a less than 90% degeneration of response compared to the contralateral side. This small study from the Mass Eye and Ear and Harvard tells us that this is actually far from clear cut and that the evidence base comes from Bell’s palsy cases rather than TB trauma.
They looked at nine patients with complete FN paralysis, four of whom underwent FN decompression. The important points are: two patients had initially reassuring ENoG results (<90% degeneration), but with a failure to improve; serial ENoGs in the following two months eventually showed more than 90% degeneration. After decompression surgery, both patients regained full/near-full facial function to House-Brackmann (HB) grades 1 and 2.
Surgery in these patients took place in the third month following the trauma. A third patient with a reassuring <90% degeneration ENoG result was conservatively managed and failed to recover beyond HB 4. Unfortunately, serial ENoG was not performed, which may have identified >90% FN degeneration. Reasons for the varied FN recovery in patients following TB trauma are given, including different immune responses in patients and variable rates of Wallerian degeneration depending on the crush injury to the FN. A flow diagram is suggested for how to treat patients and in conservatively managed cases, weekly ENoG testing is advocated for up to two months or until facial function is clinically apparent. This allows decompression surgery to take place up to three months post-trauma, with good results.
