Activation of middle-ear muscles by transcranial magnetic stimulation.

OBJECTIVES

To evaluate the reliability of transcranial magnetic stimulation in eliciting admittance changes due to activation of middle-ear muscles.

METHODS

Admittance changes induced by transcranial magnetic stimulation at the inion were evaluated in eight normal subjects, two subjects with prelingual deafness and 22 patients suffering from other otological disorders characterised by absence of acoustic reflex.

RESULTS

Responses showed a predominant negative peak in normal ears. Two small positive components, one preceding and the other following the negative deflection, were less consistently elicited. Only a positive wave was detected in otosclerotic subjects. Patients with tympanic membrane perforation or previous tympanoplasty with ossicular discontinuity did not show any response.

CONCLUSIONS

Transcranial magnetic stimulation is able to activate both stapedius and tensor tympani muscles. In conjunction with admittance audiometry, it may represent a method of exploring the mechanics of the middle ear when acoustic reflex testing is not reliable. It can be helpful in the confirmation of stapes fixation when a severe to profound hearing loss is present.