Vestibular-evoked myogenic potentials in patients with dehiscence of the superior semicircular canal

Recently Minor and co-workers described patients with sound- and pressure-i nduced vertigo due to dehiscence of bone overlying the superior semicircula r canal. Identifying patients with this "new" vestibular entity is importan t, not only because the symptoms can be very incapacitating, but also becau se they are surgically treatable. We present symptoms and findings for thre e such patients. On exposure to sounds, especially in the frequency range 0 .5-1 kHz, they showed vertical/torsional eye movements analogous to a stimu lation of the superior semicircular canal. They also showed abnormally larg e sound-induced vestibular-evoked myogenic potentials (VEMP), i.e. the shor t latency sternomastoid muscle response considered to be of saccular origin . The VEMP also had a low threshold, especially in the frequency range 0.5- 1 kHz. However, in response to saccular stimulation by skull taps, i.e. whe n the middle ear route was bypassed, the VEMP were not enlarged. This sugge sts that the relation between the sound-induced and the skull tap-induced r esponses can differentiate a large but normal VEMP from an abnormally large response due to dehiscence of bone overlying the labyrinth, because only t he latter would produce large sound-induced VEMP compared to those induced by skull taps.