Mylohyoid late responses elicited with intraoral stimulation

Many disorders affect the trigeminal nerve, highlighting the need for electrodiagnostic methods to evaluate this cranial nerve. The purpose of this study was to develop and refine clinical nerve conduction techniques for examining mylohyoid late responses and to establish normative clinical data. Intraoral stimulation of the mylohyoid nerve was performed on normal volunteers using a pediatric stimulator taped to a tongue depressor. Mylohyoid direct and late responses were recorded with surface electrodes over the mylohyoid muscles. Mylohyoid late responses with supraorbital nerve stimulation and blink reflexes were also elicited. Fifty-four subjects, 65% females, with an average age of 39.2 (standard deviation, 13.4) yr, were studied. Direct mylohyoid responses were elicited in all subjects with a mean of 1.8 (standard deviation, 0.3) ms and amplitude of 4.1 (standard deviation, 1.4) mV. Late responses occurred in 94% ipsilaterally at an average latency of 32.4 (standard deviation, 6.5) ms and in 90% contralaterally at 32.4 (standard deviation, 5.6) ms. Two distinct late responses, the second occurring at an average of 72.3 (standard deviation, 12.4) ms with intraoral stimulation were noted in 25% of subjects. Only 11% of subjects had mylohyoid late responses with supraorbital stimulation. Blink (R1) reflexes occurred in 89% (10.9 ms; standard deviation, 0.7 ms), ipsilateral R2 responses in 88% (35.2 ms; standard deviation, 3.4 ms), and contralateral R2 responses in 69% (36.2 ms; standard deviation, 4.0 ms). Mylohyoid late responses are present in most normal subjects. The neuroanatomical pathways mediating these responses require delineation. These nerve conduction techniques may be useful in evaluating patients with suspected trigeminal nerve disorders.