Mylohyoid late responses elicited with intraoral stimulation

Many disorders affect the trigeminal nerve, highlighting the need for elect rodiagnostic methods to evaluate this cranial nerve. The purpose of this st udy was to develop and refine clinical nerve conduction techniques for exam ining mylohyoid late responses and to establish normative clinical data. In traoral stimulation of the mylohyoid nerve was performed on normal voluntee rs using a pediatric stimulator taped to a tongue depressor. Mylohyoid dire ct and late responses were recorded with surface electrodes over the mylohy oid muscles. Mylohyoid late responses with supraorbital nerve stimulation a nd blink reflexes were also elicited. Fifty-four subjects, 65% females, wit h an average age of 39.2 (standard deviation, 13.4) yr, were studied. Direc t mylohyoid responses were elicited in ail subjects with a mean of 1.8 (sta ndard 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 tate responses, the second occurring at an average of 72.3 (standard deviation, 12.4) ms with intraoral stimulation w ere noted in 25% of subjects. Only 11% of subjects had mylohyoid late respo nses with supraorbital stimulation. Blink (R1) reflexes occurred in 89% (10 .9 ms; standard deviation, 0.7 ms), ipsilateral R2 responses in 88% (35.2 m s; 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 m ost normal subjects. The neuroanatomical pathways mediating these responses require delineation. These nerve conduction techniques may be useful in ev aluating patients with suspected trigeminal nerve disorders.