Motor Nerve Conduction of the Hypoglossal Nerve With F-Waves in Healthy Adults

The hypoglossal nerve is primarily responsible for tongue movement, but studies on its conduction are scarce. The F-wave, generated by antidromic depolarization of spinal motor neurons, serves as an indicator of proximal motor nerve conduction and is commonly used to assess proximal segments, particularly in distal limb nerves. Our aim was to investigate the F-wave of the hypoglossal nerve in healthy subjects.

Healthy adult volunteers underwent bilateral hypoglossal nerve F-wave testing. Recordings were obtained from the genioglossus muscles using paired monopolar needle electrodes placed 5 mm from the midline on the internal concave surface of the jaw, adjacent to the mental spines. Superficial stimulation was performed with a bipolar electrical stimulator applied to the hypoglossal nerve in the neck, one fingerbreadth below the middle third of the mandibular body. Compound muscle action potentials (CMAPs) and F-waves were recorded, with 10 to 20 stimuli applied to obtain 10 F-waves, using the shortest response for analysis.

A total of 20 participants with 40 hypoglossal nerves were studied. F-waves were successfully recorded in 39 out of 40 hypoglossal nerves, with a mean latency of 11.19 ms (IQR 8.7-20.6; SD 1.7). No significant differences in latency or amplitude were found between sides.

This study found reproducible F-waves, enabling exploration of the proximal segments of the hypoglossal nerve. These findings could be valuable for diagnostic purposes in various pathological conditions.