Significance of head-shaking nystagmus in the evaluation of the dizzy patient

In a series of studies, the phenomenon of head-shaking nystagmus (HSN) was assessed in 50 control subjects and 1364 consecutive dizzy patients who und erwent formal electronystagmography (ENG) at the Toronto Hospital Center fo r Advanced Hearing and Balance Testing. HSN was compared in a series of 30 patients who underwent conventional electro-oculography (EOG) vs magnetic ( scleral) coil eye movement recordings. Clinical correlation of HSN to other parameters of the ENG test battery was performed in another sub-series of 300 patients with known diagnoses. HSN was identified in 31.7% of dizzy pat ients vs 24% of control subjects. No significant difference in its manifest ation was noted between active vs passive head-shaking tests or on EOG vs m agnetic (scleral) coil eye movement recordings. When compared to other aspe cts of the ENG test battery, HSN was neither specific nor sensitive for ves tibular dysfunction. It nevertheless correlated well with the presence of a caloric reduction and with increasing R/L excitability differences on ENG testing. When present, HSN was characteristically monophasic in 76.8%, biph asic in 22.7% and triphasic in 0.5% of subjects. The initial direction of H SN generally obeyed Ewald's second law, but the reverse was noted in 27% wi th monophasic and 17.6% of patients with biphasic HSN. In the subseries of 300 patients with known diagnoses, the presence of HSN was statistically si gnificant (p < 0.05) in patients with peripheral vestibular dysfunction vs psychogenic dizziness. Its presence was also significant in well-documented peripheral vestibular disorders such as Meniere's disease (p < 0.01). vest ibular neuronitis (p < 0.05) and acoustic neuroma (p < 0.05). Localization of the disease involvement based on the initial direction of HSN was especi ally unpredictable in patients with Meniere's disease. The significance and usefulness of the head-shake test in the otoneurological evaluation of the dizzy patient is further commented on.