Nystagmus of paroxysmal positional vertigo: some new insights.

In most of our patients with paroxysmal positional vertigo, the paroxysm was usually short (less than 25 or 30 seconds). With the eyes deviated toward the lowermost ear, the observed nystagmus was rotatory-linear and the fast phases beat toward this ear. When the eyes were deviated to the opposite side, the fast phase of nystagmus was mainly upward linear-oblique. In a small number of patients, however, some unusual findings were observed: the nystagmus was the usual rotatory-linear, but the duration was much longer; or the nystagmus was purely horizontal; or the nystagmus was rotatory-linear, but the fast phases were in opposite direction to that usually observed. These data suggest that: the observed paroxysmal nystagmus seems compatible with excitation of the posterior or horizontal semicircular canal of the lowermost ear, or the superior canal of the uppermost ear; and singular nerve section is an appropriate treatment only if the observed paroxysmal nystagmus is compatible with excitation of a posterior semicircular canal.