Timothy C. Hain, MD
Head shaking nystagmus is the involuntary movement of the eyes that follows sinusoidal movement of the head. It is found in both normal subjects as well as patients with peripheral and central vestibular disorders. It is most useful in persons with partial vestibular lesions. Head shaking nystagmus may be a risk factor for falls.
Horizontal head-shaking is generally performed by the examiner who moves the patient's head back and forth at about a frequency of 2 hz, for 20 cycles. The usual excursion is +-30 degrees, as tolerated. Horizontal HSN is often encountered in persons with unilateral vestibular lesions (e.g. Hain et al, 1987). HSN is not very specific or sensitive to caloric weakness (Wei et al, 1989).
Vertical head-shaking is perfomed similarly in the vertical plane. Vertical HSN is less useful than horizontal. Its main utility is when a horizontal or torsional nystagmus follows vertical head-shaking, which either reflects a "latent" nystagmus, or a central cross-coupling (Hain et al, 1993).
Circular head-shaking is performed by moving the head so that the nose follows the outline of a circle, in front of the patient's head. Circular HSN is a torsional eye movement, which is commonly found in normal subjects and reflects a post-rotatory nystagmus (Hain et al, 1993; Haslwanter and Minor, 1999). Loss of circular HSN is probably abnormal and expected in persons with bilateral vestibular loss.
Head-shaking nystagmus is an indication of asymmetrical vestibular funciton. Kristindottir et al (2000) rcently reported that there is a higher frequency of HSN in hip fracture subjects than halthy subjects.