Electrical and magnetic stimulation of the intercostal nerves: a comparative study

The present study was performed in order to re-evaluate a previous report on motor nerve conduction measurement of the intercostal nerves (IN) by electrical stimulation (ES). In addition, it was aimed to compare ES with magnetic stimulation (MS). The 7th to 9th IN were investigated in 50 healthy volunteers, aged 20 to 80 years (mean age 35 +/- 16 years). The recording electrodes were placed over the cranial part of the rectus abdominal muscle. Stimulation was performed paravertebrally, and at a distance of 10 cm between stimulating and recording electrodes. The mean distal motor latency was slightly, but significantly longer after ES than MS (2.5 +/- 0.4 ms and 2.7 +/- 0.3 ms, respectively, p < 0.01). ES and MS resulted in similar mean motor nerve conduction velocities (NCV; 77 +/- 10 m/s and 79 +/- 10 m/s, respectively; p = 0.2). The amplitudes of the compound motor action potentials (CMAP) after distal stimulation versus proximal stimulation were significantly different in ES (2.5 vs. 1.9 mV; p < 0.01) and MS (3.6 vs. 1.6 mV; p < 0.001, resp.). In one subject, neither distal nor proximal ES evoked a CMAP. In eight subjects, proximal ES failed to elicit a CMAP. In all subjects, distal MS resulted in a visible CMAP, whereas in two subjects proximal MS was unsuccessful. Thus, MS proved to be significantly more effective in eliciting a CMAP (p < 0.05). Moreover, MS was agreed to be less unpleasant than ES. In summary, MS facilitates nerve conduction studies of the IN and is superior to ES regarding performance and acceptance.