Hypoglossal Nerve and Cortico-Lingual Pathway Examination using the St. Mark’s Еlectrode: a Prospective Study

INTRODUCTION. The literature describes numerous cases of mononeuropathy of the hypoglossal nerve, as a complication of various diseases, as well as after operations for symptomatic and asymptomatic stenoses in the carotid system. For a correctly selected treatment method, it is necessary to carry out a differential diagnosis between damage to the hypoglossal nerve and the cortico-lingual tract. Currently, standard diagnosis of hypoglossal nerve lesions using electroneuromyography is difficult due to methodological limitations associated with its anatomical features and variability. AIM. To demonstrate the feasibility of recording motor-wave (M-wave) in response to electrical hypoglossal nerve (HN) stimulation and motor evoked potential (MEP) in response to transcranial magnetic stimulation from the muscles of the tongue using the St. Mark’s electrode. MATERIALS AND METHODS. A prospective study was conducted on 10 healthy volunteers. To register the M-wave during electrical stimulation of HN and MEP during transcranial magnetic stimulation (TMS) from the muscles of the tongue, a St. Mark’s electrode was used. Registration was carried out sequentially from two sides of the tongue. RESULTS. In all subjects, M-wave and MEP were recorded from the muscles of the tongue from 2 sides. The average latency was in line with previously reported data in the literature. The variability of the difference in the amplitudes of the lingual motor responses was more than 50 % between the healthy volunteers. DISCUSSION. The results obtained were compared with earlier publications where normative indicators were approved. The amplitudes of the M-wave during stimulation of the HN at the proximal and distal points did not differ significantly from the literature data; the amplitude of the MEP in our study turned out to be higher, which was explained by the increased tension of the tongue muscles during the study. It was also noted that the M-wave can be recorded only at the proximal or only at the distal points of stimulation. CONCLUSION. Evaluation of conduction along the peripheral segment of the hypoglossal nerve and the cortico-lingual pathway during the abduction of muscle responses using the St. Mark’s electrode is a simple and perceptible approach to assess the functional state of the nervous structures of HN. Method for registering M-wave and MEP with the St. Mark’s electrode is safe, informative and convenient.