Clinical significance of rebound nystagmus in neuro-otological diagnosis.

The present study is concerned with a clinical analysis of 17 patients with "rebound nystagmus" examined over a period of three years. All of them have shown a short duration second degree nystagmus evoked by changes in the direction of fixation, from the lateral to straight ahead gaze. This nystagmus was a fixation nystagmus, that is to say, it was enhanced in the presence of active optic fixation and inhibited in its absence. Almost all the patients (16 out of 17) had cerebellar signs on neurological examination (in one subject rebound nystagmus was the first sign suggesting cerebellar involvement and appeared several months before any other cerebellar sign was present). Rebound nystagmus was far more common than the other neuro-otological signs suggesting cerebellar dysfunction (vestibular hyperexcitability, dysrhythmia in postcaloric nystagmus and ocular dysmetria). In three out of four patients with unilateral lesions rebound nystagmus was ipsilateral with respect to the side of the lesion. Postmortem studies were carried out upon five cases and showed either pathological changes in the cerebellum or a lesion involving the cerebellar peduncles in the brain stem.