Hearing Safety From Single- and Double-Pulse Transcranial Magnetic Stimulation in Children and Young Adults

Abstract

Introduction Concerns regarding hearing safety have limited the number of studies using transcranial magnetic stimulation (TMS) in children and young adults. The objective of this study was to examine the safety of TMS with regards to hearing in a group of 16 children and young adults (17.3 ±4.9 years) with and without brain injury. Methods Pure-tone hearing thresholds and distortion-product otoacoustic emissions were measured before and after exposure to single- and paired-pulse TMS (1–2 sessions of 149–446 TMS pulses at a median of 49%–100% maximum stimulator output over a 2.2 hour period). Results No mean change in hearing outcomes was noted. In addition, no clinically significant change in hearing threshold was observed in any participant, and participants did not experience a subjective change in hearing following TMS exposure. Conclusions Single- and double-pulse TMS administered within the parameters used in this study, which included hearing protection, can be used in children and young adults without impacting hearing. This study provides further evidence for hearing safety after TMS exposure in children and young adults.

Sound comparison of seven TMS coils at matched stimulation strength

“…On the other hand, compared to the previous peak SPL measurement using a head phantom [7], we obtained lower SPL for the same coil (Magstim 70mm Double Coil): 105 dB(C) in the acoustic far field versus 127.6 dB(C) in the ear canal in the near field. This difference is only partially explained by the smaller distance between the ear and the coil.…”

“…Due to these side effects, the TMS safety consensus group suggested in 2009 that "the acoustic output of newly developed coils should be evaluated and hearing safety studies should be conducted as indicated by these measures" [4]. Since then, specific stimulatorecoil combinations have been evaluated with hearing safety measurements [6,7], and a comparison between coils has been published [2,12]. We extend this previous work by quantifying the impulse characteristics of the airborne TMS sound and comparing the measurements of seven coils at normalized stimulation strengths.…”

Sound comparison of seven TMS coils at matched stimulation strength

“…On the other hand, compared to the previous peak SPL measurement using a head phantom [5], we obtained lower SPLs for the same coil (Magstim 70mm Double Coil, 108 dB(Z) in free field versus 127.6 dB(C) in the ear canal). This difference is only partially explained by the smaller distance between the ear and the coil.…”

“…The sound pulse can potentially cause hearing loss. This risk can be mitigated with adequate hearing protection [3][4][5]. However, should the hearing protection fail, TMS can cause permanent hearing loss [6].…”

“…Due to these side effects, the TMS safety consensus group suggested in 2009 that "the acoustic output of newly developed coils should be evaluated and hearing safety studies should be conducted as indicated by these measures" [9]. Since then, specific stimulator-coil combinations have been evaluated with hearing safety measurements [4][5], and a comparison between coils has been published [10]. To address methodological limitations of the latter, namely sound level measurements intended only for continuous (i.e., not impulsive) sounds based on IEC 61672 [2], and to expand the range of compared devices, we conducted measurements of the coil click in a total of seven coils for three stimulators and normalized the stimulation strength across the various configurations.…”