Facial neuropathy is the most common cranial neuropathy. The anatomy of the facial nerve is complex, with a long intracranial course. Electrodiagnosis can be helpful in determining prognosis, but such studies are not helpful until several days after the onset of the neuropathy. The clinical presentation shows unilateral weakness of the upper and lower parts of the face, hyperacusis, dysgeusia, and abnormal lacrimation and salivation. Seventy percent of cases are idiopathic, or they can be regarded as Bell’s palsy. Ramsay Hunt syndrome, also known as herpes zoster oticus, is another common cause of facial neuropathy.

The electrodiagnostic methods commonly used to study the facial nerve are direct facial motor nerve conduction studies, needle electrode electromyography of facial-innervated muscles, and the blink reflex. Electrodiagnostic studies are quite useful for the determination of demyelinating pathology or axonopathy. Wallerian degeneration of motor fibers takes 5–8 days after an axonal injury, and assessment of prognosis is possible only after this period.