A 55-year-old woman had paroxysms of vertigo and visual blurring assoc
iated with complex combined torsional, horizontal, and vertical nystag
mus. These episodes occurred regularly at 2-minute intervals, each att
ack lasting for 15 seconds. Between attacks, there was a much finer as
ymptomatic nystagmus whose components were in the opposite direction t
o those associated with the paroxysmal attacks. A brain MRI revealed a
n arteriovenous malformation in close proximity to the left vestibular
nucleus, with evidence of previous bleeding. Caloric testing demonstr
ated a left-sided vestibular paresis. We suggest that neurons in this
patient's damaged left vestibular nucleus are usually underactive but
regularly produce pathologic brief bursts of hyperactivity causing epi
sodic reversal and gross exacerbation of her resting nystagmus. Treatm
ent with low-dose carbamazepine was successful in abolishing both the
paroxysms of nystagmus and the symptoms of vertigo and visual disturba
nce.