Abstract

Background
and Objective: Head-shaking nystagmus (HSN) is induced by head oscillation in the yaw or pitch plane at 2 Hz for approximately 20 s. The HSN test has been reported to be a sensitive screening test for the presence of peripheral and central vestibular disorders. Perverted head-shaking nystagmus (pHSN) refers to the nystagmus that develops in the plane other than that being stimulated by head shaking, i.e., downbeat or upbeat head shaking nystagmus (HSN) after horizontal head shaking. It has been considered to be a central pattern of HSN. Little data is available regarding how frequently pHSN occurred and its significance in central as well as in peripheral vestibular disorders. Our goal of this study was to determine the clinical significance of the HSN and pHSN in patients with peripheral and central vestibular disorders.
Methods
We reviewed the medical records of 822 consecutive subjects who were referred to a dizziness clinic of Chonbuk National University hospital from January 2010 to December 2010. Neurologic examination including the video oculography (VOG) in darkness for 60 sec before head shaking, during head shaking, and for 100 sec after head-shaking were undertaken. HSN was considered to develop when the post-head-shaking nystagmus last at least 5 beats with latency from the end of head-shaking of no more than 5 sec, and a velocity at least 3 °/sec.
Results
In healthy control group, spontaneous nystagmus (SN) was observed in 2.2% (1/45), HSN was observed in 17.8% (8/45), perverted HSN was observed in 6.7% (3/45). In patients with peripheral vestibular disorder group, SN was observed in 14.1% (56/397), HSN was observed in 40.6% (161/397), perverted HSN was observed in 9.8% (39/397). In patients with central vestibular disorder group, SN was observed in 17.5% (38/217), HSN was observed in 24.0% (52/217), perverted HSN was observed in 13.4% (29/217). In unspecified dizziness group, SN was observed in 1.9% (4/208), HSN was observed in 13.0% (27/208), perverted HSN was observed in 1.9% (4/208). Perverted HSN was frequently observed in central vestibular disorders such as stroke, vestibular migraine, cerebellar ataxia, and vertebro-basilar insufficiency (VBI). However, pHSN was also observed at higher rate than expected in peripheral vestibular disorders including BPPV especially involving the vertical canals, Meniere disease and even in the unilateral vestibulopathy (39/397, 9.8%).
Conclusions
Our results show that the perverted HSN in dizzy populations was frequently observed not only in cases of central vestibular disorders but also in peripheral disorders. Perverted after head-shaking nystagmus can develop by any conditions that cause the difference in the vestibular velocity storage in vertical component of vestibular-ocular reflex.

• Keywords: nystagmus; vertigo; vestibular ocular reflex ; head shaking nystagmus;