The clinical efficacy of head shaking nystagmus (HSN) were studied in 170 patients complaining of vertigo, dizziness or hearing loss. The over all provocation rate of HSN was 69% (117/170), which was much higher than that of spontaneous, positional or positioning nystagmus. Even in patients tested long after a vertigo attack, HSN was easily provoked. In the majority (95%) of the patients with caloric abnormality, the deficiency type of HSN (briskly beating nystagmus immediately after head shaking) towards the contralateral side of canal paresis (CP) was observed. The number of nystagmus beats increased as head shaking continued. These results suggest that HSN is provoked by the accumulation of dominant stimulation to the normal lateral semicircular canal.
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