To define a disorder characterized by recurrent spontaneous vertigo (RSV) of unknown etiology and interictal headshaking nystagmus (HSN).
We characterized HSN in 35 patients with RSV-HSN compared to that recorded in randomly selected patients with compensated vestibular neuritis (VN), vestibular migraine (VM), and Ménière disease (MD).
The estimated time constant (TC) of the primary phase of HSN was 12 seconds (95% confidence interval [CI] 12-13) in patients with RSV-HSN, which was larger than those in patients with VN (5 seconds, 95% CI 4-5), VM (5 seconds, 95% CI 5-6), or MD (6 seconds, 95% CI 5-6). TCs of the horizontal vestibulo-ocular reflex were also larger during the rotatory chair test in patients with RSV-HSN. Among the 35 patients with RSV-HSN, 7 showed vigorous long-lasting HSN with a peak slow-phase velocity >50.0°/s. In 5 patients (5 of 7, 71%) with vigorous HSN, HSN could have been induced even with headshaking for only 2 to 5 seconds. Long-term prognosis was favorable, with a resolution or improvement of the symptoms in more than half of the patients during the median follow-up of 12 (range 2-58) years from symptom onset. None developed VM, MD, or cerebellar dysfunction during the follow-up.
The clinical features and characteristics of HSN in our patients indicate a hyperactive and asymmetric velocity-storage mechanism that gives rise to intermittent attacks of spontaneous vertigo probably when marginal compensation of underlying pathology is disrupted by endogenous or exogenous factors.