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Differences in vulnerability of the orbicularis oculi and oris muscles in intratemporal facial nerve paralysis clinical and experimental studies


Practica Otologica Kyoto 78(2): 249-268
Differences in vulnerability of the orbicularis oculi and oris muscles in intratemporal facial nerve paralysis clinical and experimental studies
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 the present investigation. From the orbicularis oculi and the oris muscles of both the healthy and diseased side, the evoked electromyograms and the electromyograms using surface electrodes, and the strength-duration curves. Comparative analysis of the data obtained from these examinations revealed no difference in these 2 muscles of the healthy side. On the diseased side, the following results suggested a more pronounced vulnerability of the nerve branch innervating the orbicularis oculi muscle. The average amplitude of the electromyogram and the amplitude of evoked electromyogram were significantly smaller in the orbicularis oculi muscle than in the oris muscle. A more marked decline in the averaged amplitude of the electro-myogram of the orbicularis oculi muscle was noted in subjects with denervation confirmed by the strength duration curve. The same phenomenon was apparent in the subjects whose facial paralysis score was low. Supportive evidence indicated that the recovery of the orbicularis oculi muscle was retarded in comparison to that of the oris muscle. The clinical findings prompted the following animal study. In guinea pigs, a transient palsy of the infrastapedial lesion of the facial nerve was made by clamping the nerve for 5 s. Electromyographic responses of both the orbicularis oculi and oris muscles evoked by direct electrical stimulation at the suprastapedial portion were recorded simultaneously. The clamping was then informed by using a microsurgical needle holder of which the compression force was 1.6 kg/mm. Duration of the conduction block in the 2 muscles was measured using the supramaximal threshold of the responses of both muscles. In 13 animals a longer conduction block was noted in the orbicularis oculi muscle than in the orbicularis oris muscle. In 2 animals conduction block disappeared simultaneously in the 2 muscles and no palsy of both muscles was observed in 1 animal. This experimental study supported the result of the clinical investigation that the intratemporal facial nerve fibers innervating the orbicularis oculi muscle is more vulnerable than the orbicularis oris muscle branch. Microscopic study revealed that the average diameter of the nerve fibers innervating the orbicularis oculi muscle is significantly larger than that of the nerve fibers innervating the oris oculi muscle. This observation suggests the fragility of the nerve fibers innervating the orbicularis oculi muscle.


Accession: 005151747

DOI: 10.5631/jibirin.78.249



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