Electrophysiological study of direct and reflex responses evoked in facial muscles of normal and polyneuritic subjects.

Abstract

Direct and reflex responses evoked in facial muscles by percutaneous electrical stimulation are analyzed in 30 normal subjects, in 29 unselected patients with polyneuritis in the lower limbs and in 6 subjects with retrogasserian neurotomy. The early trigemino-facial reflex component can be evoked in the m. orbicularis oris by stimulation of a wide facial area corresponding roughly to the innervation territory of the third trigeminal division. Its latency remains fairly stable independent of the point of stimulation and it is not abolished by a supramaximal stimulation recruiting all the motor fibers of the facial nerve. It is concluded that the cutaneous origin of this early reflex response in the orbicularis oris muscle is likely. Several observations suggest that its afferents run at least partly in the buccal nerve. It is not abolished either by a homolateral retrogasserian neurotomy with preservation of the trigeminal motor root or by local anaesthesia of the homolateral infra-orbital and mental nerves. Furthermore the shortest latency is generally observed when the stimulation electrode is applied at the point of exit of the buccal nerve before its arborisation to the skin of the face. Because of the often observed difficulty in getting a reflex response without preceeding motor response, it is suggested that the anastomoses between the buccal and the facial nerve can contain this afferent fibers. In polyneuritic syndromes of various etiology an early involvement of the facial nerve is demonstrated. Whereas the shortest conduction times of the direct response fall within the normal range in most of the patients, the duration of the direct and the reflex response is shown to be pathological in most of them. Moreover electromyographic signs of partial denervation of facial muscles are found in some patients. It is suggested that the analysis of direct and reflex responses in facial muscles could be used as a complementary test in the diagnosis of polyneuritis.