Enhanced Auditory Sensitivity to Body Vibrations in Superior Canal Dehiscence Syndrome

Abstract

A key feature of superior canal dehiscence (SCD) syndrome is supranormal hearing of body sounds. The aim of the present study was to quantify this phenomenon and to ascertain whether auditory sensitivity to body vibrations can distinguish SCD patients. Hearing thresholds in response to vibration at the vertex, at the spinous process of the 7th cervical vertebra, and at the medial malleolus were tested in 10 SCD patients and 10 controls. Both patients and controls had insert earphones in both ears. The insert in the test ear was blocked while masking was presented to the other ear. Vibration in the frequency range of 125-1,000 Hz was presented to each of the 3 stimulation sites. The SCD patients were found to have significantly lower hearing thresholds compared with controls. The two study groups reacted differently with respect to frequency. The SCD patients showed an enhanced sensitivity for the lower stimulus frequencies. The difference was, however, rather independent of stimulus presentation site. The findings suggest that hearing thresholds in response to low-frequency body vibration at sites distant from the ears can distinguish SCD patients. The present findings may also support the idea that auditory sensation to body vibrations is a response related to soft tissue conduction.

Superior Semicircular Canal Dehiscence Syndrome

“…26 Additionally, patients with SCDS can occasionally hear a 512-Hz tuning fork in the affected ear when placed distally, such as against the medial malleolus. 29,30…”

Investigation of Mechanisms in Bone Conduction Hyperacusis With Third Window Pathologies Based on Model Predictions

“…This means that AC sound thresholds are elevated at low frequencies while the BC thresholds improve at low frequencies (BC hyperacusis) resulting in a low-frequency air-bone gap (ABG) ( 7 ). Other manifestations of a third window in SSCD is autophony (hearing one's own voice as loud or distorted) as well as pulsatile tinnitus and hearing of one's own footsteps ( 8 ). Even hearing of eye movements has been reported ( 9 ).…”

“…The low-frequency effect on the AC hearing has been well-investigated in clinical studies ( 8 , 10 – 12 ), animal experimental studies ( 13 ), cadaveric temporal bone studies ( 14 , 15 ), and mathematical modeling ( 16 ). A usual explanation of the low-frequency AC threshold worsening in SSCD is that the open communication between the vestibule and the cranial space through the semi-circular canal allow sound energy to leak out through this open pathway instead of going to the RW and thereby stimulating the BM.…”

“…The low-frequency effects on BC hearing in SSCD are not equally well-understood as the AC effects. The manifestation of increased low-frequency BC sensitivity, termed BC hyperacusis, is well-established ( 7 , 8 ) but the mechanisms for this improvement has not been investigated in detail. One suggestion is that the reduced impedance in the vestibule side of the inner ear enhances the volume velocity in the inner ear during BC, known as BC fluid inertia ( 16 , 22 ).…”

Soft tissue conduction is the third mode of auditory stimulation

“…hearing. These include sites on the head not over skull bone, on the neck, chest, back [5 , 6] , eye [7][8][9] and the ankle (in patients with superior canal dehiscence) [10] . STC can be easily demonstrated by blocking the external ear canal (e.g.…”