6

Acute Progressive Bilateral

Ophthalmoplegia with Mental

Status Change

CASE NO. 6

A 33-year-old man was brought to the ER because of a change in his mental status. His wife related that the patient was fine the previous day. However, on that day that he was brought in for evaluation, she noticed his confusion. His past medical history was remarkable for hypertension controlled with hydrochlorothiazide, and high cholesterol controlled with diet and exercise.

On examination, the patient was somnolent and also confused on attempts to measure his visual acuity. The ocular motility showed limitation of up-gaze. Pupillary examination showed light-near dissociation of the pupils OU. Slit lamp examination and funduscopic examinations were within normal limits.

Discussion

Dr. Brazis. The acute onset of mental status changes and ocular signs is most consistent with a cerebral infarct or hemorrhage. The impairment of upward gaze and the light-near dissociation of the pupils may be localized to the dorsal midbrain. With the dorsal midbrain syndrome, there is impairment of all upward eye movements (although the vestibuloocular reflex and Bell’s phenomenon may sometimes be spared). Down-gaze saccades and smooth pursuit may be impaired, but downward vestibuloocular movements are spared.

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Emergencies in Neuro-Ophthalmology: A Case Based Approach

Downbeating nystagmus may be present. The upper eyelid may be retracted, baring the sclera above the cornea (Collier’s “tucked lid” sign); this sign is probably due to damage to posterior commissure levator inhibitory fibers or is a manifestation of normal levator — superior rectus synkinesis. Bilateral ptosis may result when the lesion extends ventrally to involve the caudal central nucleus of cranial nerve III. The pupils are large and react poorly to light, but the near response is spared (light-near dissociation). Occasionally, skew deviation with the higher eye on the side of the lesion is noted. Convergence and divergence are often impaired. In some patients, convergence spasm may result in slow or restricted abduction (“midbrain pseudo-sixth”) during horizontal refixations. Attempted up-gaze may result in convergence-retraction nystagmus, with quick adducting-retraction jerks. This phenomenon can be elicited at the bedside by having the patient watch a downward-moving optokinetic drum. In this case, the normal upward corrective saccades are replaced by convergence-retractory nystagmus, which is made up not by convergence movements but by opposed adducting saccades at least in some cases. The retraction of the eye into the orbit results from irregular co-firing of several extraocular muscles perhaps due to impairment of recurrent inhibition with the oculomotor subnuclei or abnormal vergence activity. Fixation instability with square-wave jerks may also be noted.

Tumors are most often responsible for damage of the dorsal midbrain. Hydrocephalus is another common etiology, especially when dilation of the third ventricle and aqueduct or enlargement of the suprapineal recess causes pressure on and deformity of the posterior commissure. Patients with shunted hydrocephalus may develop features of the pretectal syndrome with shunt dysfunction even without any dilation of the ventricular system or elevation of intracranial pressure; thus, the observation of these clinical features provides a sensitive index of shunt dysfunction regardless of ventricular size or isolated measurements of intracranial pressure. Less common causes of pretectal syndrome include thalamic or midbrain hemorrhage or infarction, hypoxia, multiple sclerosis, trauma, lipid storage

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Acute Progressive Bilateral Ophthalmoplegia with Mental Status Change

diseases, Wilson’s disease, drugs (e.g. barbiturates, carbamazepine, neuroleptics), Whipple’s disease, syphilis, and tuberculosis. Upward gaze is often limited in Parkinson’s disease and may be rarely affected with vitamin B12 deficiency.

Occlusive vascular disease of the rostral basilar artery, usually embolic, frequently results in the “top of the basilar” syndrome due to infarction of the midbrain, thalamus, and portions of the temporal and occipital lobes. This syndrome may also occur in patients with giant basilar artery tip aneurysms, in patients with vasculitis, and after cerebral angiography. This syndrome variably includes:

•Disorders of eye movements: Unilateral or bilateral paralysis of upward or downward gaze, disordered convergence, pseudoabducens palsy, convergence-retraction nystagmus, ocular abduction abnormalities, elevation and retraction of the upper eyelids (Collier’s sign), skew deviation, and lightning-like eye oscillations.

•Pupillary abnormalities: Small and reactive, large or midposition and fixed, light-near dissociation, corectopia, occasionally oval pupil.

•Behavioral abnormalities: Somnolence, peduncular hallucinosis, memory difficulties, agitated delirium.

•Visual defects: Homonymous hemianopia, cortical blindness, Balint syndrome.

•Motor and sensory deficits.

Course. Indeed, the patient’s MRI demonstrates restricted diffusion within the thalami bilaterally, consistent with acute ischemia (Fig. 6.1A). Circle of Willis 3D MIP angiography demonstrated complete occlusion of the distal basilar artery (Fig. 6.1B).

If the criteria for intravenous or intra-arterial tPA are satisfied (see Case No. 2) and the deficit was less than three hours in duration, tPA treatment should be considered. Whether tPA is given or

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Emergencies in Neuro-Ophthalmology: A Case Based Approach

Fig. 6.1. Axial diffusion (A) demonstrates restricted diffusion within the bilateral thalami (circle) consistent with acute ischemia. Circle of Willis 3D MIP angiography

(B) demonstrates complete occlusion of the distal basilar artery (arrow).

not, the patient should be admitted for evaluation of the etiology of the top of the basilar syndrome and for treatment of stroke risk factors.

Dr. Lee. In the modern neuroimaging era, patients can undergo a CT and sometimes an MRI within hours of presentation. If the studies are performed this acutely the structural imaging can be normal. A patient with an apparently unilateral and presumed “ischemic” third nerve palsy can have a normal CT and MRI. If bilateral ocular motor cranial neuropathy signs appear, then the differential diagnosis includes Bickerstaff’s encephalitis, botulisum, Miller-Fisher variant, myasthenia gravis, Wernicke syndrome and Whipple’s disease. The normal neuroimaging may give rise to a false sense of security, however, if DWI is not included in the study. The DWI might show bright signal (i.e. restricted diffusion) bilaterally due to “top of the basilar” thrombosis producing acute ischemia at the mesencephalic-thalamic junction, even though the initial structural studies are normal.

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