Acute vertical pendular nystagmus: eye-movement analysis and review of the literature.

Vertical pendular nystagmus (PN) rarely occurs with acute pontine lesions. To hypothesize a pathophysiology for acute vertical PN, we analyzed the clinical characteristics and quantitative eye-movement recordings of one new case with acute vertical PN and an additional 11 patients from the literature. Most patients had extensive pontine lesions causing either the locked-in syndrome or unresponsiveness, but two conscious patients had focal lesions restricted to the paramedian caudal pontine tegmentum. All patients presented a complete or partial horizontal gaze palsy, and about half showed ocular bobbing before or during the appearance of vertical PN. The vertical oscillations were conjugate at a frequency of 1-5 Hz, and the amplitudes were variable, ranging from 0.2° to 40°. The peak velocities were asymmetric in some patients, faster with downward movements. About half of the patients developed palatal tremor several weeks or months after presenting with acute vertical PN. Based on the location of the lesions and results of eye-movement recordings, we suggest two possible mechanisms for acute vertical PN; oscillations originating in the inferior olives due to disruption of the central tegmental tract or low-velocity saccadic oscillations caused by omnipause neuron damage.