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Show J. Clin. Neuro-ophthalmol. 4: 35-37, 1984. Sustained Upgaze in Coma TSUTOMU NAKADA, M.D. INGRID L. KWEE, M.D. HENRY LEE, M.D. Abstract Sustained upgaze is a rare phenomenon that is observed primarily in those patients with coma secondary to cardiac arrest or prolonged hypotension. Because of "selective vulnerability" of the brain, cardiac arrest or prolonged hypotension may produce both cerebral and cerebellar cortical damage sparing the brain stem vestibulo-ocular reflex (VOR) pathways. This selective damage may be responsible for the generation of sustained upgaze. The VORs receive their selective inhibition from the cerebellar flocculus. This inhibition is exerted on only one of the two VOR pathways converging on each extra-ocular muscle, so that total disinhibition of the VOR pathway activities will result in a tonic upward bias. The underlying neuronal mechanism of sustained upgaze appears to be due to total floccular disinhibition resulting in upward drift produced by the biased VOR and the lack of correcting saccades due to cerebral dysfunction releasing the brain stem ocular motor systems from their control. Sustained upgaze is a phenomenon seen in the comatose patient who suffered from cardiac arrest or prolonged, severe hypoxia. l Its underlying neuronal mechanism, however, is still uncertain. We observed a case of sustained upgaze that was inducible by noxious stimuli accompanied by brief decorticate posturing. We propose the neuronal mechanism generating sustained upgaze based on the selective inhibition of the vestibuloocular reflexes (VORs) by the cerebellar flocculus. Case Report A 54-year-old alcoholic female was admitted for an acute confusional state. She had known alcoholic liver disease, recurrent hepatic encephalopathy, hypertension, and chronic renal failure. On admission, she was alert, but agitated and confused. She was oriented to herself, but not to date and place. The presumptive diagnosis of From the Department of Neurology. University of California. Davis. Veterans Administration Medical Center. Martinez. California. March 1984 hepatic encephalopathy was made, for which she received lactulose. A more extensive workup was scheduled for the following morning. However, she remained agitated throughout the night and was given a total of 8 mg of morphine. Subsequently, she developed cardiorespiratory arrest. She was successfully resuscitated, but remained comatose. On neurological examination, she was comatose. No spontaneous movements including myoclonic jerks were observed. The eyes were closed. The pupils were equal and reactive. The doll's eyes maneuver produced full conjugate movements of the eyes in all directions. The corneal reflex was present bilaterally. Her extremities were flaccid. With noxious stimuli applied to the sternum, she had brief decorticate posturing and concomitantly opened her eyes exhibiting sustained, conjugate upward deviation of the eyes. Computed tomography failed to disclose any abnormalities. Electroencephalogram (EEG) showed a "burst-suppression" pattern. Brain stem auditory evoked potentials were normal. The patient remained comatose without spontaneous movements or eye opening. Sustained upgaze was noted for the following 6 days with noxious stimuli. She expired on the 13th day of hospitalization. Discussion The vestibulo-ocular reflex (VOR) arc is formed by specific receptor-effector connections. Stimulation of each semicircular canal produces excitation of a specific extraocular muscle and inhibition of its antagonist in each eye. 2 Inhibitory projections from the floccular Purkinje cells reach the ipsilateral vestibular nucleus and selectively inhibit certain VOR pathway activities, namely, all the anterior semicircular canal pathway and half of the horizontal semicircular canal pathway activities. 2 The six VOR pathways and their floccular inhibition based on the study in the rabbit are summarized in Table 1. 2 The effects of disinhibition on the two horizontal semicircular canal pathways activities are self-cancelling. However, the effects of disinhibition on the vertical semicircular canal pathways are synergistic due to the 35 Sustained Upgaze TABLE 1. Vestibulo-Ocular Reflex Pathways and their Floccular Inhibition' Anterior Excitatory i-Superior rectus Yes c- Inferior oblique Yes Inhibitory i-Inferior rectus Yes c-Superior oblique Yes Horizontal Excitatory i-Medial rectus Yes c-Lateral rectus No Inhibitory i-Lateral rectus Yes c-Medial rectus No Posterior Excitatory i-Superior oblique No c- Inferior rectus No Inhibitory i-Inferior oblique No c-Superior rectus No Note: i-ipsilateral; c-contralateral. 'Based on the study of the rabbit by Ito et al.' absence of inhibition on the posterior semicircular canal pathways. Therefore, total disinhibition of the VOR activities produces a tonic upward bias. An imbalance in the VOR activities produced by VOR pathway disruption or its disinhibition has been suggested to produce certain types of eye movement abnormalities. 3 - 5 Since sustained upgaze is observed primarily in patients who suffered from severe anoxia, we proposed the following hypothesis for the underlying neuronal mechanism of sustained upgaze. Certain structures of the brain are more susceptible to anoxic insult. These include the third layer of the neocortex, the outer halves of the striatum, the globus pallidus, the anterior and dorsomedian nuclei of the thalamus, the vulnerable sectors of the hippocampus, the Purkinje and basket cells of the cerebellum." Therefore, severe anoxia may produce both cerebral and cerebellar cortical dysfunction sparing the brain stem VOR pathways and ocular motor systems. Total disinhibition of the VORs from the cerebellar flocculus results in upward bias producing conjugate upward deviation of the eyes. The lack of cerebral control results in failure to induce correcting saccades producing the observed sustained upgaze. In his review of 17 cases of sustained upgaze in coma, Keane emphasized the integrity of brain stem functions in all cases. 1 Positive corneal reflexes, full conjugate eye movements with the Canals Extraocular Muscles Floccular Inhibition doll's eyes maneuver, and the normal BAEPs observed in our patient are supportive of preserved brain stem functions. Furthermore, the sustained upgaze induced by noxious stimuli in our patient suggests that not only preserved, but also disinhibited brain stem reflexes may play the major role in its pathogenesis. The decorticate posturing, one of the disinhibited brain stem posturing reflexes, accompanying the sustained upgaze in our patient further supports a state of disinhibition of certain brain stem reflexes. Downbeat nystagmus has been suggested to result from vertical VOR imbalance due to disinhibition. 3 Therefore, sustained upgaze and downbeat nystagmus may be two different manifestations of the same imbalance in the vertical VOR activities under different cerebral influences. The well-known caloric testing provides a model for this concept. Irrigation of the external auditory canal with cold or warm water establishes a temperature gradient in the inner ear. The horizontal semicircular canal develops the largest temperature gradient because it lies closest to the stimulus. In the same position, the anterior semicircular canals are less affected and the posterior semicircular canals are hardly affected at al!.? In the supine position with the head tilted 30° up, irrigation with warm water increases the tonic discharge of the ampullary nerves. The effects on the two horizontal canals are in opposition, while those on the anterior semicircular canals are in the same direction. Therefore, bilateral irrigation produces cancellation of the horizontal semicircular canal influences and allows for the minor anterior semicircular canal effects to become appreciable. Bilateral irrigation with warm water produces an upward drift. In the conscious subject, correcting saccades are triggered resulting in downbeat nystagmus. The lack of correcting saccades in comatose patients results in sustained, upward deviation of the eyes.s Total disinhibition of the VORs from the flocculus results in an upward bias of the VOR similar to that of bilateral warm water caloric testing due to the selective nature discussed earlier. With correcting saccades, it manifests as downbeat nystagmus, while without correcting saccades, it manifests as sustained upgaze. Three of the five patients of sustained upgaze in Keane's series who survived for longer than 1 month (one of whom regained consciousness) subsequently developed downbeat nystagmus. This transition from sustained upgaze to downbeat nystagmus may indeed signify the recovery of cerebral cortical function and its influence on the brain stem oculomotor system. Interestingly, the downbeat nystagmus reportedly occurred especially when the patients appeared "aroused:) a state which may increase cortical influences. Journal of Clinical Neuro-ophthalmology References 1. Keane, j.R.: Sustained upgaze in coma. Ann. Neural. 9: 409-412,1981. 2. Ito, M., Nishimaru, N., and Yamamoto, M.: Specific patterns of neuronal connexions involved in the control of the rabbit's vestibuloocular reflexes by the cerebellar flocculus. f. Physiol. 265: 833854, 1977. 3. Baloh, R.W., and Spooner, j.W.: Downbeat nystagmus: A type of central vestibular nystagmus. Neurology 31: 304-310, 1981. 4. Nakada, T., and Kwee, I.L.: Floccular inhibition of the vestibulo-ocular reflex in man. f. Clin. Neuroophthalmol. 2: 201-207, 1982. 5. Nakada, T., and Remler, M.P.: Primary position upbeat nystagmus: Another central vestibular nys- March 1984 Nakada, Kwee, Lee tagmus? f. Clin. Neuro-ophthalmol. 1: 185-189, 1981. 6. Brierly, J.B.: Cerebral hypoxia. In Greenfield's Neuropatlwlogy, W. Blackwood and j.A.N. Corsellis, Eds. Edward Arnold Ltd., London, 1976, pp. 5556. 7. Dejong, R.N.: The Neurologic Examination (4th ed.). Harper & Row, New York, 1979, pp. 216-218. 8. Plum, F., and Posner, j.B.: The Diagnosis of Stupor and Coma (3rd ed.). F. A. Davis Co., Philadelphia, 1980, pp. 54-57. Write for reprints to: Tsutomu Nakada, M.D., Department of Neurology, University of California, Davis, Veterans Administration Medical Center, 150 Muir Road, Martinez, California 94553. 37 |
