Abstract
The secondary phase of paroxysmal positional nystagmus was observed in five patients with paroxysmal positional vertigo. In all five, positional and/or positioning rotary nystagmus appeared for 20 to 30 seconds in the head-hanging and/or the lateral head position with a short latency of crescendo and decrescendo in character, associated with vertiginous sensation, and it was followed by the secondary phase nystagmus involving rotation to the opposite direction for more than 45 seconds in the same head position. Head MRI or head CT findings were normal in 4 cases, but a small pontine infarction was detected in one patient. There was no other evidence of ear disease, and neurological examination revealed nothing abnormal even in the patient with the pontine lesion in MRI. The secondary phase of BPPV is clinically rare and it is still unknown whether the origin is peripheral or central. Review of the literature introduced that the secondary phase of BPPV might be caused by movements of debris in the posterior semicircular canal, abnormal function in short term adaptation, or other transient dysfunction of the central nervous system.
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