When paroxysmal positioning vertigo isn't benign.

The electronystagmographic auditory brainstem response and magnetic resonance imaging findings for a 33-year-old male with a 3.5 cm left vestibular schwannoma are presented. Of particular interest was the presence of an unusual positioning nystagmus following the Dix-Hallpike maneuver in the right head-hanging position. The patient demonstrated a nystagmus that was immediate in onset and not fatigueable upon repeated positioning. During positioning, the patient experienced a vertical bobbing sensation and dysphoria, but not rotational vertigo. Most importantly, the nystagmus had a predominant downbeating vertical component. the case illustrates the diagnostic significance of downbeating nystagmus elicited by the Dix-Hallpike maneuver.