Ocular vestibular evoked myogenic potentials to head tap and cervical vestibular evoked myogenic potentials to air-conducted sounds in isolated internuclear ophthalmoplegia.
OBJECTIVE
The central pathways responsible for ocular vestibular evoked myogenic potentials (VEMPs) to forehead tapping remain to be determined. This study aimed to determine whether the medial longitudinal fasciculus (MLF) carries the signals for ocular VEMPs (oVEMPs) in response to this mode of stimulation.


METHODS
Twelve patients with isolated unilateral internuclear ophthalmoplegia (INO) due to brainstem infarction underwent evaluation of the ocular tilt reaction (ocular torsion and skew deviation), tilt of the subjective visual vertical (SVV), cervical VEMPs (cVEMPs) in response to tone burst sound, and oVEMPs induced by tapping the forehead.


RESULTS
Eight (67%) patients showed abnormal oVEMPs that included no wave formation (n=4) and decreased amplitude (n=3) in the lesion side, and bilaterally absent responses in the remaining patient. Furthermore, the patients showed diminished oVEMPs responses in the lesion side compared with normal side (6.0 ± 5.6 vs. 11.7 ± 5.5 μV, paired t-test, p=0.001) and increased IADamp(%) of the oVEMPs compared with normal controls (43.6 ± 41.2 vs. 9.1 ± 6.2, t-test, p=0.018). In contrast, cVEMPs were abnormal in only three (25%) patients, decreased (n=2) or no response in the lesion side. Eleven (92%) patients showed contraversive ocular tilt reaction or SVV tilt.


CONCLUSIONS
Patients with INO frequently show impaired formation of ipsilesional oVEMPs in response to forehead tapping. The occasional abnormality and decreased amplitude of ipsilesional cVEMPs also suggest a modulatory pathway for the inhibitory sacculocollic reflex descending in the MLF.


CONCLUSIONS
This study suggests that the MLF contains the fibers for the otolith-ocular reflex from the contralateral ear.
Kangwon National University College of Medicine, Chuncheon, South Korea; Biomedical Research Institute, Seoul National University Bundang Hospital, South Korea.
Hyo-Jung
HJ
Kim
Department of Neurology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, South Korea.
Jong Hee
JH
Lee
Department of Neurology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, South Korea. Electronic address: jisookim@snu.ac.kr.
Ji-Soo
JS
Kim
D001844:Bone Conduction / Q000502:physiology; D020526:Brain Stem Infarctions / Q000150:complications; D002150:Caloric Tests; D005260:Female; D006309:Hearing / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015835:Ocular Motility Disorders / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D010037:Otolithic Membrane / Q000502:physiology; D011446:Prospective Studies; D011930:Reaction Time; D012018:Reflex / Q000502:physiology; D058585:Vestibular Evoked Myogenic Potentials
Internuclear ophthalmoplegia; Medial longitudinal fasciculus; Ocular tilt reaction; Vertigo; Vestibular evoked myogenic potentials