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Show Journal of Neuro- Ophthalmology 15( 4): 236- 240, 1995. i 1995 Lippincott- Raven Publishers, Philadelphia Lid Nystagmus as a Sign of Intrinsic Midbrain Disease Michael C. Brodsky, M. D. and Frederick A. Boop, M. D. A 6- year- old boy with signs and symptoms of ocular myasthenia gravis had lid nystagmus evoked by horizontal gaze. MR imaging demonstrated an intrinsic midbrain lesion, which was diagnosed by biopsy as a low-grade astrocytoma. In the setting of ocular myasthenia gravis, the finding of lid nystagmus may serve as a useful clinical sign of intrinsic midbrain disease. Key Words: Lid nystagmus- Ocular myasthenia- Ophthalmoplegia- Midbrain tumor. The terms " lid nystagmus," " upper lid jerks," and " lid hopping" have been applied to a rare neuro- ophthalmic phenomenon in which a series of rapid, rhythmical, upward jerking movements of the upper lids occur alone or in conjunction with specific movements of the eyes or head ( 1- 14). Clinical reports suggest that this phenomenon occurs in the setting of posterior fossa disease ( 1). We describe a child with bilateral ptosis and diffuse ophthalmoplegia suggestive of ocular myasthenia gravis in whom the atypical finding of lid nystagmus led to the diagnosis of midbrain astrocytoma. Manuscript received July 18, 1994. From the Department of Ophthalmology ( M. C. B.), and Neurosurgery ( F. A. B.), University of Arkansas for Medical Sciences, Little Rock, Arkansas, U. S. A. This study was supported in part by a grant from Research to Prevent Blindness, Inc. Address correspondence and reprint requests to Dr. Michael C. Brodsky, Arkansas Children's Hospital, 800 Marshall, Little Rock, AR 72202, U. S. A. CASE REPORT A healthy 6- year- old boy was referred for evaluation of gradually progressive exotropia and bilateral upper eyelid ptosis of 6 months duration. His mother stated that the ptosis was usually mild upon awakening and worse as the day progressed. There was no history of headaches, nausea or vomiting, mental status changes, decreased motor strength, or difficulty swallowing or chewing. There was no family history of ptosis or ophthalmoplegia. Facial examination demonstrated a severe bilateral ptosis and a large exotropia ( Fig. 1). Corrected visual acuity was 20/ 20 in each eye. The pupils were equal in size and normally reactive to light, with no afferent pupillary defect. Extraocular movements were mildly limited in all fields of gaze with a severe adduction deficit in the right eye as shown in Fig. 2. Horizontal and vertical sac-cades were slow in all directions. The patient was unable to converge his eyes. He had no nystagmus when he looked straight ahead in his exotropic position of gaze, but developed a gaze- evoked nystagmus in horizontal and vertical gaze. He usually fixated objects of interest with his left eye which necessitated a compensatory right face 236 LID NYSTAGMUS 237 FIG. 1. Facial photograph demonstrating bilateral upper eyelid ptosis and exotropia. turn and a slight chin elevation. He had 45 diopters of exotropia in all fields of gaze except for left gaze where his exotropia increased to greater than 90 diopters. Horizontal pursuit movements or saccades in either direction evoked a large- amplitude upper lid nystagmus that lasted for the duration of horizontal gaze. Each abnormal lid movement consisted of a rapid, conjugate, upward jerk of both lids that was followed immediately by a slower downward drift to the original ptotic position. During horizontal pursuit movements, the lids jerked at a frequency of approximately one cycle per second. Careful examination of videotapes disclosed no associated vertical movement of the eyes. In sustained lateral gaze, the lid nystagmus continued as a horizontal gaze- paretic nystagmus supervened. During attempted upgaze, the lid nystagmus increased in amplitude and coincided with a large-amplitude, synchronous upbeating nystagmus. Attempted upgaze produced no visible retraction movements of the globes. During fixation of a stationary object, an occasional spontaneous upward jerk of the lids was observed. The patient had a positive Cogan's lid twitch sign. He displayed equivocal levator fatigability; however, his ptosis improved noticeably after 30 minutes of sleep. Intramuscular injection of neostigmine 0.8 mg produced no visible change in his ptosis or ophthalmoplegia. Results of a neurological examination were otherwise normal. A magnetic resonance ( MR) scan of the head demonstrated a 2- cm mass with low signal intensity on Tl - weighted images and high signal intensity on T2- weighted images within the midbrain tegmentum ( Fig. 3). There was mild enlargement of the ventricular system with sparing of the fourth ventricle secondary to compression of the aqueduct of Sylvius. Results of a stereotactic biopsy revealed a low- grade astrocytoma. The patient was treated with radiation therapy consisting of 5,400 cGy over a 6- week period. Two FIG. 2. Versions in secondary positions of gaze demonstrating diffuse ophthalmoplegia with marked adduction lag in the right eye. / Neuro- Ophthalmol, Vol. 25, No. i, 1995 238 M. C. BRODSKY AND F. A. BOOP FIG. 3. MR images demonstrating intrinsic midbrain lesion. Left: T2- weighted ( TR = 2500; TE = 90) axial MR image demonstrating large intrinsic hyperintense midbrain glioma. Right: T1- weighted ( TR = 700; TE = 11) sagittal image ( postgadolinium) demonstrating the rostrocaudal extent of the tumor. years after initial presentation, he is attending public school and appears to be functioning normally except for mild speech impairment. His parents state that his ptosis has resolved, but his ex-otropia persists. DISCUSSION Upper lid nystagmus is considered pathological when it occurs in the absence of synchronous vertical movements of the globes. Nystagmus- like jerking of the upper lids has been described in numerous pathological conditions. In each case, the abnormal lid movements have been evoked by specific movements of the eyes or head. Most previously reported cases can be subdivided into lid nystagmus evoked by convergence ( Pick's sign) and lid nystagmus evoked by horizontal gaze. Convergence- evoked lid nystagmus was first reported in 1916 by Pick ( 2) in a patient who had multiple sclerosis and spastic quadriparesis. The lid nystagmus was observed in primary gaze in the absence of bulbar nystagmus. The lid movements became accentuated during convergence and also upgaze, where a synchronous upbeating nystagmus appeared. Pick ( 2) hypothesized that lid nystagmus may reflect abnormal excitation within the oculomotor nuclei radiating to the cell bodies that control levator function. Rohmer and colleagues ( 3) noted convergence- induced lid nystagmus in a patient with a posttraumatic dorsal midbrain syndrome and a left third nerve palsy. Sanders and coworkers ( 4) described convergence-induced lid nystagmus induced by convergence in a patient with a cerebellar sarcoma that filled the fourth ventricle. Safran and coworkers ( 5) described convergence- induced lid nystagmus in two patients cerebellar system disease and speculated that a phasically initiated instability of cerebellar origin might disrupt the normal physiological increase in levator tonus that occurs during convergence. As an alternative hypothesis, they suggested that convergence- evoked lid nystagmus might also represent the effect of gaze- evoked nystagmus of cerebellar origin upon the normal physiological eyelid retraction evoked by convergence. Salisachs and Lapresle ( 6) noted convergence- evoked lid nystagmus in patient with Miller Fisher syndrome. Howard described the same phenomenon in a patient with a pontomedullary angioma ( 7). Gaze- evoked lid nystagmus was first reported in 1916 by Popper ( 8) in an alcoholic patient with a left- beating vestibular nystagmus. Sittig ( 9) and Wilbrand and Saenger ( 10) subsequently described gaze- evoked lid and ocular nystagmus in patients clinical signs of brainstem dysfunction without further clinical or pathological localization. Daroff and colleagues ( 11) described a patient with lateral medullary syndrome who had lid nystagmus that was evoked by lateral gaze and inhibited by convergence. The fact that our patient's lid nystagmus occurred in the absence of any visible vertical move- / Neuro- Ophthalmol, Vol. 15, No. 4, 1995 LID NYSTAGMUS 239 ment of the globes led us to conclude that the abnormal lid movements somehow resulted from the abnormal innervational milieu created by his slowly growing tegmental tumor. In upgaze, the amplitude of the lid nystagmus increased as a large- amplitude upbeating nystagmus supervened, suggesting that the observed lid movements in upgaze were, at least in part, secondary to the ocular nystagmus. The pathophysiology of lid nystagmus in unknown. In this case, however, its neuroanatomical substrate can clearly be localized to the midbrain tegmentum. Our patient's neuroophthalmic findings suggest a combined disturbance of supranuclear ( periodic firing of paretic levator muscles during lateral and upward pursuit movements), nuclear ( bilateral upper eyelid ptosis), and possibly internuclear ( selective impairment of adduction) pathways. His bilateral ptosis was similar to that described in previous reports of " midbrain ptosis," which is attributable to a dorsal midbrain lesion involving cell bodies of neurons that bilaterally innervate the levator muscles in the central caudal nucleus ( 12- 16). Midbrain ptosis can occur as an isolated finding or in combination with diffuse ophthalmoplegia, internuclear ophthalmoplegia, or third nerve palsy ( 17,18). Our patient's slow abducting saccades suggested that descending pathways for horizontal gaze were also affected, albeit to a lesser degree ( 17,18). Intracranial compressive lesions involving the brainstem and cavernous sinus can occasionally present with clinical findings indistinguishable from myasthenia gravis ( 19- 22). Our patient had signs and symptoms of ocular myasthenia gravis ( a history of minimal ptosis upon awakening with worsening as the day progressed, absence of pain, absence of pupillary involvement, and a positive Cogan's lid twitch sign). Horizontal eye movements in myasthenia gravis are occasionally accompanied by twitching or fluttering movements of the upper lids; however, lid nystagmus is uncharacteristic of neuromuscular junction disease. The absence of levator fatigability, the presence of slow saccades with minimal limitation of ocular rotations, and the negative Prostigmine test called the diagnosis of myasthenia gravis into further question and led us to order MR imaging to rule out a mass lesion. Ragge and Hoyt ( 23) recently described a similar child with neurofibromatosis and a midbrain glioma who had bilateral fatigable ptosis, diffuse ophthalmoplegia, a positive Cogan's lid twitch sign, and a negative Tensilon test. Interestingly, their patient had unilateral " lid hopping," which was characterized by a momentary elevation or fluttering of the ptotic eyelid as the patient visually pursued an object from one position of lateral gaze to another. The ptosis resolved following radiation therapy to the tumor. Ragge and Hoyt ( 23) attributed the patients neuro- ophthalmic signs to " midbrain myasthenia" and hypothesized that tumor infiltration within the midbrain may have critically reduced acetylcholine levels at centrally located acetylcholine synapses ( most likely at the synapses between supranuclear pathways in the brainstem and the nuclear complex of the third nerve), resulting in fatigable ptosis. The similar myasthenic presentation of a midbrain tegmental tumor in our case raises the possibility that lid nystagmus may be a neuro- ophthalmic sign of " midbrain myasthenia." Conceivably, lid nystagmus in the setting of an intrinsic midbrain lesion could require a combination of ( a) an intermittent conduction block at the synaptic junction of supranuclear neurons of the posterior commissure with the central caudal nucleus ( midbrain myasthenia), and ( b) nuclear involvement at the level of the central caudate nucleus. 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