Conduction abnormalities of the facial and trigeminal nerves in polyneuropathy.

Facial and trigeminal nerve involvement in polyneuropathy was assessed by the evoked action potential of the orbicularis oculi muscle following direct stimulation of the facial nerve (direct response) and the two component blink reflex elicited by stimulation of the trigeminal nerve (R1 and R2). The latencies of the direct and R1 responses were increased substantially in the Guillain-Barré syndrome (GBS), chronic inflammatory polyneuropathy (CIPN), and hereditary motor and sensory neuropathy (HMSN Type I), and to a much lesser degree in diabetic polyneuropathy (DPN). The study was normal with rare exceptions in the Fisher syndrome (FS) and HMSN Type II. The latency ratio of R1 to the direct response showed a mild increase in GBS, a moderate decrease in CIPN and HMSN Type I, and a mild decrease in DPN. We conclude that these simple electrophysiologic techniques can provide useful, objective information in determining the degree and distribution of cranial nerve lesions.