Abstract
Often in Audiology and Neurotology the focus is on disorders characterized by loss of
hearing and vestibular function. A complementary approach is to look at the manifestations
of abnormally augmented auditory or vestibular functions, commonly named auditory and
vestibular hypersensitivity. The present thesis deals with several aspects of a prototype of
hypersensitivity syndrome, the superior canal dehiscence syndrome (SCDS). This relatively
rare syndrome is characterized by cochlear and vestibular hypersensitivity to sound and
vibrations, but also to pressure stimulation which normally has no influence on hearing or
balance. By use of a recently introduced vestibular test method, vestibular evoked myogenic
potentials (VEMP), it is possible to obtain an objective measure of vestibular sensitivity to
sound and vibrations. The thesis describes the background to the research field presenting:
the normal function of the ear, the function in presence of conditions giving sound/vibration
and pressure hypersensitivity (third mobile window syndromes), a detailed description
regarding the superior canal dehiscence syndrome and the vestibular evoked myogenic
potentials. The thesis then presents and discuss in details the four scientific papers which are
the core of this research project.
In the first paper a new vestibular evoked myogenic method is presented. This method, based
on low frequency bone conducted stimulation, showed a high diagnostic ability for SCDS,
especially valuable in those sporadic conditions when other methods, based on sound
stimulation, cannot be applied.
The second paper presents a new approach for testing the cochlear hypersensitivity to body
sounds. This phenomenon, expressed clinically by the symptom autophony, is particularly
evident in SCDS. The study showed that it is possible to retrieve a measure of the internal
body sound hypersensitivity by means of a specific audiometric application based on the
delivery of bone conducted stimuli at distance sites and not at the mastoid as normally
performed.
The third paper is a comparative study on the actual ocular VEMP (oVEMP) methods
investigating their diagnostic ability for SCDS in a large cohort of dizzy patients. The study
confirmed the diagnostic superiority of oVEMP evoked by sound stimuli over the two other
methods based on oVEMP evoked by bone conducted stimuli.
In the fourth paper SCDS the diagnostic ability of sound induced VEMP protocols is studied.
The testing is performed at reduced stimulus intensity levels according to the newly released
recommendation on acoustic stimulation restrictions during VEMP testing. Specifically,
VEMP was tested at sound intensity levels compatible with safe acoustic exposure levels in
audiological testing. The study showed that these reduced sound levels did not affect the
diagnostic accuracy of VEMP for SCDS. This is clinically relevant, as it will make it possible
to carry out a SCDS diagnosis even among patients affected by abnormal acoustic
susceptibility.
