Difference in vulnerability of the orbicularis oculi and oris muscles in intratemporal facial nerve paralysis.

A total of 30 patients with intratemporal facial palsies of recent onset, 20 with Bell's palsy and 10 with Ramsay Hunt's syndrome, were the subjects of this investigation. From the orbicularis oculi and the oris muscles of both the healthy and the diseased side, evoked electromyograms and electromyograms were obtained using surface electrodes, and strength-duration curves were derived. Comparative analysis of the data obtained from these examinations revealed no difference in these two muscles of the healthy side. On the diseased side, however, the following results suggested a more pronounced vulnerability of the nerve branch innervating the orbicularis oculi muscle than of that innervating the orbicularis oris muscle. 1) The average amplitudes of the electromyogram and of the evoked electromyogram were significantly smaller in the orbicularis oculi muscle than in the oris muscle. 2) A more marked decline of the averaged amplitude of the electromyogram of the orbicularis oculi muscle was noted in the subjects with denervation proved by the strength-duration curve. 3) The same phenomenon was also apparent in the subjects whose facial paralysis score was low.