P221 Comparison of threshold tracking SICI measurements using circular and figure of eight coils

Threshold tracking transcranial magnetic stimulation (TT-TMS) is suggested as a novel diagnostic tool for amyotrophic lateral sclerosis (ALS). A standard recommendation is to use a figure of eight coil instead of a circular coil for TMS, but the studies on ALS use a circular coil when measuring short interval intracortical inhibition (SICI). The aim of this study was to compare TT-SICI measurements, reproducibility and pain and discomfort using figure of eight and circular coils. Twenty healthy controls (9 females and 11 males) underwent 4 examinations each on the same day with TT-TMS including measurement of SICI-parameters. Two were performed with each coil and the degree of pain and discomfort during the examinations were rated from 0 to 10 (NRS-score). The change in SICI between ISIs of 1 and 2 ms was higher for the figure-of-eight coil (5.91 ± 1.96) than for the circular coil (−1.655 ± 1.11) (p = 0.002). No other significant differences were found in the ISIs. There was no difference in reproducibility between the two coils, but both coils showed wide intervals between their limits of agreement suggesting that several measurements should be made for each person to ensure reliability. The circular coil is associated with higher NRS-scores (2.80 ± 1.61) than the figure of eight coil (1.95 ± 1.36) (p = 0.025), but the difference is so small that this should be given little importance when choosing a coil type. Further research should focus on coil comparison for patient populations as well.