The Laryngoscope Lippincott Williams & Wilkins, Inc., Philadelphia 0 1999 The American Laryngological, Rhinological and Otological Society, Inc.

Clinical Significance of Rebound Nystagmus Chao-Yu Lin, MD; Yi-Ho Young, MD

ObjectiuelHypothesis: Magnetic resonance imag- ing (MRI) examination is performed in cases of re- bound nystagmus to elucidate the responsible site for rebound nystagmus. Methods: Patients with vertigo or tinnitus received a battery of audiological and neuro-otological tests. Those who had rebound nys- tagmus were rechecked by electronystagmography and examined by MRI. Results: Ten patients had a second-degree nystagmus evoked by changing direc- tion of fixation, from the lateral to the forward gaze. All patients displayed positive MRI findings in cere- bellum or brainstem, including tumor in seven cases and stroke in three cases. Moreover, in seven of eight cases with unilateral lesions, rebound nystagmus was ipsilateral with respect to the side of the lesion. Con- clusion: Rebound nystagmus implies a lesion in cere- bellum or brainstem for which MRI examination is 100% sensitive. It has a certain lateralizing value, with its direction away from the lesioned side. Key Words: Rebound nystagmus, cerebellum, brainstem, electro- nystagmography, magnetic resonance examination.

Lurynguscupe, 1091803-1805,1999

INTRODUCTION Rebound nystagmus is a type of nystagmus that oc-

curs when a patient returns the eyes to the primary posi- tion after a prolonged attempt a t an eccentric gaze. Quick phases of the nystagmus are away from the direction of a previously attempted eccentric gaze. Previous investiga- tions have suggested that rebound nystagmus reflects a transient bias created by the central nervous system, e.g., cerebellum, in an attempt to hold an eccentric gaze.l.2 However, the source of the bias of rebound nystagmus remains unknown. Therefore, in this study, we perform magnetic resonance imaging (MRI) examination in cases of rebound nystagmus to elucidate the site responsible for the rebound nystagmus.

PATIENTS AND METHODS From October 1991 to September 1998, 9156 patients with

vertigo or tinnitus were encountered at the Department of Oto- laryngology, National Taiwan University Hospital. All patients received a battery of tests including detailed history, physical

-. __ Prom the Department of Otolaryngology, National Taiwan Univer-

sity, Taipei, Taiwan. Editor’s Note: This Manuscript was accepted for publication July 19,

1999. Send Reprints Request to Yi-Ho Young, MD, Department of Otolar-

yngology, National Taiwan University Hospital, 1 Chang-Te Street, Taipei, Taiwan. E-mail: youngyh@ha.mc.ntu.edu.tw

examination, neurological examination, blood examination, plain radiographic examination (including mastoid, internal auditory canal, and cervical spine), audiometry, and electronystagmogra- phy (ENG). All 9156 patients were subjected to all tests without exception. Those who had rebound nystagmus detected by either the naked eye or ENG were rechecked by ENG and followed up by MRI examination. Once MRI examination revealed brain tumor, a patient was referred to neurosurgeons for surgical extirpation and the diagnosis was confirmed by histopathological study.

RESULTS Among the 9156 patients, 10 patients (0.1%) showed

rebound nystagmus by ENG. Eight were men and two were women. Their ages ranged from 16 to 61 years (mean average, 42 y). ENG results revealed bilateral gaze nys- tagmus, abnormal eye tracking, and abnormal optokinetic nystagmus in all cases, abnormal visual suppression in eight cases, and no caloric response in seven cases. Eight cases had unilateral and two cases had bilateral rebound nystagmus. Their clinical presentations included tinnitus (80%), ataxia (60%), hearing impairment (60%), vertigo (40%), or headache (30%). All patients displayed positive MRI findings representing 100% sensitivity. Their final diagnoses were as follows: cerebellopontine angle schwan- noma in three, cerebellar anaplastic astrocytoma in one, brainstem astrocytoma in one, brainstem lymphoma in one, cerebellopontine angle meningioma in one, cerebellar hemorrhage in one, dissecting aneurysm of vertebral ar- tery in one, and dolichoectasia of vertebrobasilar artery in one (Table I).

Seven of the eight patients having unilateral rebound nystagmus were ipsilateral with respect to the side of the lesion. Figure 1 illustrates patient 2, a 48-year-old man with rebound nystagmus from right lateral gaze to for- ward gaze, MRI examination revealed a lesion occupying a 3 x 3 x 2-cm space in the right cerebellopontine angle (Fig. 2). Pathology revealed schwannoma after operation. Figure 3 illustrates patient 6, with rebound nystagmus from left lateral gaze to forward gaze. Again, MRI re- vealed a lesion in a 4 x 4 X 3-cm space in the left cerebel- lopontine angle (Fig. 4) that was confirmed on pathologi- cal investigation as a schwannoma. Thus the correlation between the direction of unilateral rebound nystagmus and lesioned side was prevalent in seven of eight cases (87.5%).

DISCUSSION Several observations involving the characteristics of

rebound nystagmus in patients and monkeys provide fur-

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TABLE I. Summary of Clinical Information.

Patient Age Lesion Provocation No. (y) Sex Diagnosis Side Direction

1 48 M

2 48 M

3 25 M

4 44 M 5 16 M 6 31 F

7 61 F

8 56 M 9 28 M

10 28 M

Cerebellopontine angle meningioma Cerebellopontine angle schwannoma Cerebellar anaplastic astrocytoma Brainstem astrocytoma Brainstem lymphoma Cerebellopontine angle schwannoma Cerebellopontine angle schwannoma Cerebellar hemorrhage Dissecting aneurysm of vertebral artery Dolichoectasia of vertebrobasilar artery

R R + F

R R + F

R R + F

R R + F R R + F L L + F

L L + F

L R - t F L R + F , L - t F

B R - t F , L - + F

- - ___ R -+ F: unilateral rebound nystagmus occurred when patient returned

from right lateral gaze to forward gaze; L + F: unilateral rebound nystagmus occurred when patient returned from left lateral gaze to forward gaze.

ther insight into the neural structures involved in gener- ating rebound nystagmus waveforms. Yamazaki and Zee3 recorded rebound nystagmus in a patient with a tumor initially involving the cerebellar flocculus. One year later when the tumor apparently invaded the brainstem in the region of the vestibular nuclei, the rebound nystagmus disappeared. As in our patient with cerebellopontine angle schwannoma (Figs. 1 and 21, rebound nystagmus was absent in this patient 1 month after surgery.

Animal experimentation demonstrated that rebound nystagmus appeared in monkeys only after they recovered

l i l i l l l l l l l l l l l l l l l I I I l l l l l l R F

Fig. 1. A 48-year-old man with rebound nystagmus from right lateral gaze (R) to forward gaze (F), with its direction beating to the left (healthy) side (away from the lesioned side). First trace is time base at 1 mark per second. Second trace is nystagmic movement. Third trace is differentiated eye movement indicating eye velocity.

Fig. 2. Same patient as in Figure 1. Magnetic resonance imaging revealed a lesion occupying a 3 x 3 x 2-cm space in the right cerebellopontine angle.

from an injection of neurotoxins in the medial vestibular nucleus and the nucleus of prepositus hypoglossi.4J Both studies suggest that the medial vestibular nucleus and the nucleus of prepositus hypoglossi areas of the brainstem (the site of the neural integrator for horizontal eye movements) are critical for generating the bias that cre- ates rebound nystagmus.

Clinically, rebound nystagmus is most frequently en- countered in patients with cerebellar lesions involving the flocculus and paraflo~culus.1~5.~ The cerebellum, which plays an essential role in stabilizing gaze, is assumed to play a role in generating rebound nystagmus through the following mechanisms. During eccentric fixation, the cer- ebellum participates in the velocity bias that opposes drift eye movements.7.8 Whereas during central fixation, through gaze stabilization systems (i.e., smooth pursuit

y ~ ~ * - - . ~ ~ - ~ * - -

Fig. 3. A 31-year-old woman with rebound nystagmus from left lateral gaze (L) to forward gaze (F), with its direction beating to the right (healthy) side (away from the lesioned side). First trace is time base at 1 mark per second. Second trace is nystagmic movement. Third trace is differentiated eye movement indicating eye velocity.

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1804 Lin and Young: Rebound Nystagmus

Fig. 4. Same patient as in Figure 3. Magnetic resonance imaging revealed a lesion occupying a 4 x 4 x 3-cm space in the left cerebellopontine angle.

and fixation), the cerebellum mediates the rapid discharge of the rebound nystagmus velocity bias. This observation implies that the cerebellum simultaneously promotes and impedes the appearance of intense rebound nystagmus.

Laryngoscope 109: November 1999

Therefore, we infer that rebound nystagmus is a clinical sign for lesion in cerebellum or brainstem.

Morales-Garcia et aL9 proposed that rebound nystag- mus was ipsilateral with respect to the side of the lesion. In our patients seven (87.5%) of eight who had unilateral rebound nystagmus were ipsilateral with respect to the lesioned side. The only exception was one patient who experienced left-sided cerebellar hemorrhage. This hem- orrhage may be attributed to multiple hemorrhage focus, not only in cerebellum but also in the brainstem.

CONCLUSION Rebound nystagmus implies a lesion in the cerebel-

lum or brainstem for which MRI examination is 100% sensitive. It has a certain lateralizing value, with its di- rection away from the lesioned side.

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