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Show }. Clin. Neuro-ophtha/mo/. 1: 191-193, 1981. The Association of Periodic Alternating Nystagmus with Periodic Alternating Gaze A Case Report C. KENNARD, M.D. * G. BARGER, M.D. W. F. HOYT, M.D. Abstract A 26-year-old man with a recurrent cerebellar medulloblastoma developed periodic alternating nystagmus. During radiation treatment, a bilateral voluntary horizontal gaze paresis appeared, and the periodic alternating nystagmus was replaced by periodic alternating gaze. Several days later, full eye movements returned, as did the periodic alternating nystagmus which had an identical periodicity to the periodic alternating gaze. The underlying pathophysiology of periodic alternating nystagmus and periodic alternating gaze is discussed. Introduction Periodic alternating nystagmus is a form of eye movement disorder of a congenital or acquired type in which spontaneous nystagmus alternates in direction. I. 2 In those cases with the acquired type, the pathological lesion is usually in the pontomedullary region. 3 . 4 Periodic alternating gaze is a rare cyclic disorder of eye movements in which the eyes are conjugately deviated to one side for a period of time followed by a conjugate movement of the eyes to the opposite side. Two types of patients have been described with different periods, and probably different underlying mechanisms. Several comatose patients had periodic alternating gaze with a period of 3-5 seconds, which has been given the descriptive title "Ping-pong" gazer, They were found to have acute bilateral cerebral disease without a specific localized lesion.6-H Two patients had periodic alternating gaze with a longer period of 1-2 minutes. They were both alert and were considered to From the Neuro-Ophthdlmology Unit, Depdrtments of Neurology, Neurologicdl Surgery dnd Ophthdlmology, University of Cdlifomid, Sdn Frdncisco, Cdlifornid. • Present address: Neurological Deparment, The London Hospital. Whitechapel. London, El lBB, England. September 1981 have brain-stem lesions due to vasculo-occlusive disease.~' 10 We report a patient with a cerebellar medulloblastoma who developed periodic alternating nystagmus which subsequently, in association with a bilateral voluntary horizontal gaze paresis, changed to periodic alternating gaze for several days before reverting back to periodic alternating nystagmus. Case Report In November 1978, a 24-year-old male student presented with a 4-month history of lethargy, headaches, and unsteadiness associated with recurrent brief episodes of aphasia and right-sided numbness. On examination, he was found to have bilateral gaze-evoked nystagmus, more marked on gaze to the left than to the right, and mild leftsided ataxia. A contrast-enhanced CAT scan showed moderate hydrocephalus with an enhancing lesion in the region of the anterior vermis, which appeared to compress the fourth ventricle. There were also some supratentorial areas of enhancement. A ventriculo-atrial shunt was inserted, followed several days later by a posterior fossa craniotomy which revealed a large medulloblastoma filling the fourth ventricle, infiltrating the cerebellar hemispheres more on the left than on the right. and extending down to the level of the arch of C-l. A subtotal resection was performed, and he was subsequently transferred to the University of California, San Francisco, for further treatment. There he received a course of craniospinal irradiation which was augmented by hydroxyurea. Following irradiation, clinical examination revealed a mild bilateral gaze-evoked nystagmus and mild left-sided ataxia. A CAT scan still showed a small area of enhancement in the region of the fourth ventricle. There was no change in the patient's condition until he developed lethargy and intermittent diplopia and worsening ataxia in April of 1980. CAT 191 Periodic Alternating Nystagmus scan showed an increase in the size of the fourth ventricuLu enhancing mass, as well as two new subependymal enhancing lesions in the left frontal horn .md left lateral ventricle. He was started on a course of Procarbazine, CCNU, and Vincristine. Six weeks later the patient complained of blurred vision in addition to his intermittent diplopia. Examination now revealed periodic alternating nystagmus in the presence of a full range of eye movements. The periodic alternating nystagmus regularly reversed direction with a period of approximately 180 seconds. No other change in his neurological status was noted. A repeat CAT scan performed in July 1980, some 3 weeks after the onset of the periodic alternating nystagmus, showed little change. He was started on a course of Dibromodulcitol and also received Baclofen 5 mg t.i.d. for his periodic alternating nystagmus. 11 After I week the periodic alternating nystagmus had not changed, and the drug was stopped because of side effects. In September 1980, the repeat CAT scan showed an increase in the size of both enhancing lesions, his ataxia had worsened, and it was therefore decided to start a further course of radiotherapy. After two treatments he complained of difficulty moving his eyes. Examination revealed an absence of voluntary horizontal eye movements with a full range of vertical eye movement, although vertical saccades weerI' thought to be slower than normal. Horizontal oculocephalic and optokinetic responses were absent, but it was noted that there was periodic alternating gaze. The eyes would be conjugately deviated 20° to the opposite side, this movement taking approximately 10 seconds. They would remain deviated to this side for a further 80-90 seconds before the cycle was repeated. The periodic alternating gaze, therefore, had a period of approximately 180 seconds. Further examination revealed limb ataxia, more marked on the left than the right, and an ataxic gait. A CAT scan at this time showed further rostral extension of the fourth ventricular enhancing mass to the level of the midbrain. Daily radiotherapy was continued, and 4 days later he could voluntarily move his eyes 10° horizontally. After a further 4 days, he now had a full range of horizontal eye movements, and his periodic alternating nystagmus had returned. A typical sequence was 80 seconds beating to the left, then a pause of IS seconds, followed by 80 seconds beating to the right and a pause of IS seconds. Thus, the period was 190 seconds. The amplitude of the nystagmus was increased by gaze in the direction of the fast component; gaze away decreased it. Upward and downward gaze did not affect the horizontal beats. Optokinetic nystagmus could be produced only when the slow component of his spontaneous nystagmus was near a null point or in the same direction as the stimulus. Six weeks 192 after the completion of irradiation, the patient's periodic alternating nystagmus was still present, but less intense. Discussion The patient, who had a previously resected medulloblastoma, developed periodic alternating nystagmus at a time of observed recurrence of the tumor in the region of the fourth ventricle. The subsequent loss of voluntary horizontal eye movements with the development of periodic alternating gaze suggested bilateral involvement of the parapontine reticular formation 12 which could have been due to tumor invasion, edema, or compression. Certainly the tumor appeared to have enlarged even further when the periodic alternating gaze developed, possibly into the pontine tegmentum itself, but without pathological confirmation it is impossible to determine the exact cause for the patient's para pontine reticular formation failure. The pathophysiology of periodic alternating nystagmus is incompletely understood. It has been suggested that this type of nystagmus may result from alternating hyperexcitability of the vestibular nuclei on either side of the brain stem. 13 This hyperexcitability could result from damage to the cerebellovestibular inhibitory projections which arise from the archicerebellum. 14 This region was specifically damaged in our patient by a medulloblastoma with resection and subsequent tumor recurrence. It is known that there are strong commissural connections between the vestibular nuc1ei),'; which may provide the anatomical substrate for alternating vestibular nucleus activity once their cerebellar inhibition has been removed. Such activity would produce a periodic shift of the null region as proposed by Daroff and Dell'Osso.16 This is the region in which the drift forces upon the eye are equal. If the null region was, for example, to the right, with optic fixation in the primary position of gaze, the eyes would tend to drift to the right with corrective saccades taking the eye back on target. This would result in a left-beating nystagmus. A shift of the null region to the left would reverse the nystagmus which would then beat to the right. At the time our patient developed periodic alternating gaze, he had a loss of voluntary conjugate horizontal eye movement in either direction. This indicates a bilateral lesion of the parapontine reticular formation with a failure of the generation of horizontal saccades. Since the cycle time of this patient's periodic alternating nystagmus and periodic alternating gaze was almost identical, we infer that this periodic alternating gaze demonstrated the underlying conjugate drifts of periodic alternating nystagmus in which the normally occurring corrective saccades were absent. Kesten- Journal of Clinical Neuro-ophthalmology baum~ proposed a similar relationship between periodic alternating gaze and periodic ..lltern.lting nystagmus, although his patient had only periodic alternating gaze. This finding in our p..ltient supports the shifting null region hypothesis as the underlying mechanism for both periodic ..llternating gaze and periodic alternating nyst.lgmus. References 1. Davis. D.G., and Smith, J.L.: Periodic alternating nystagmus. Am. r Ophtha/mo/. 72: 757-702. 1971. 2. 6aloh, R.W.. Honrubi.l, V., .md Konrad, H.R.: Periodic alternating nystagmus. Brain 99: 11-20, 1970. 3. Keane. J.R.: Periodic alternating nystagmus with downward beating nystagmus. Arch. Neural. 30: 339-402, 1974. 4. Towle, P.A., and Romanul, F.: Periodic alternating nystagmus: First pathologically studied case. Neurology (Minn. ) 20: 408, 1970. 5. Senelick, R.C: "Ping-pong" gaze: Periodic alternating gaze deviation. Neurology (Minn. ) 26: 532-535, 1976. 6. Steward, JD., Kirkham, T.H., and Mathieson, G.: Periodic alternating gaze. Neurology 29: 222-224, 1979. 7. Fisher. CM.: Some neuro-ophthalmological observations. f. Neuro/. Neurosurg. Psychiatry 30: 383392. 1907. 8. Von Cramon, D., and Zihl, J.: Das Phanbmen der periodisch alternierenden 6ulbus deviation. Arch. Psychiatr. Nervenkr. 224: 247-257, 1977. 9. Kestenbaum, A.: Clinical Methods of Neuro- September 1981 Kenn..Hd, B..Hger, Hoyt ophthd/m%gic EXdminJtion. Crune & Stratton, New York, 1901. 10. Coldberg, R.T., Gonzalez, C, Breinin, G.M, et al.: Periodic alternating gaze deviation with dissociation of head movement. Arch. Ophtha/mol. 73: 324-330, 1065. 11. Halmagyi, G.M., Rudge, P., Gresty, M.A., et al.: Treatment of periodic alternating nystagmus. Ann. Neuro/. 8: 609-011, 1980. 12. O.uoff, R.B., and Hoyt, W.F.: Supranuclear disorders of ocular control systems in man: Clinical, anatomical, and physiological correlations. In The Control of Eye Movements, P. Bach-y-Rita, CC Collins, and J.E. Hyde, Eds. Academic Press, New York, 1971. 13. Meienberg, 0., and Hoyt, W.F.: Oculomotor control disorder during the neutral phase of periodic alternating nystagmus. f. Neurol. 223: 309-312, 1980. 14. Walberg, F.: Cerebello-vestibular relations: Anatomy. Progr. Brain Res. 37: 361-376, 1972. 15. Brodal, A.: Organisation of the commisural connections: anatomy. Progr. Brain Res. 37: 167-176, 1972. 16. Daroff, R.B., and Dell'Osso, L.F.: Periodic alternating nystagmus and the shifting null. Can. f. Oto/aryngo/. 3: 367-371, 1974. Acknowledgements Christopher Kennard held an Alexander Werhner fellowship from the Medical Research Council and a Keeler Award. Write for reprints to: Dr. C Kennard, PhD., M.R.CP., Neurological Department, The London Hospital, Whitechapel, London, El 166, England. 193 |
