Neuro-ophthalmology Question of the Week: Abnormal Lateral Gaze

Figure: (A) Ocular motor examination (right gaze, straight gaze, left gaze).1

Question: Which of the following are correct?
1. These eye movements are consistent with alternate skew in lateral gaze
2. These eye movements are consistent with over action of the inferior oblique muscles 
3. These eye movements are consistent with supranuclear lesions
4. These eye movements are consistent with lesions of the cerebellum
5. These eye movements are consistent with pretectal lesions
6. These eye movements are consistent with lesions of the cervico-medullary junction

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Figures:

(A) Ocular motor examination (right gaze, straight gaze, left gaze).

(B) Diffusion-weighted imaging (left) and apparent diffusion coefficient images (right) reveal a focal and acute ischemic stroke1

Correct Answers: all are correct

Explanation: “A 63-year-old patient was admitted with acute ataxia and binocular oblique diplopia. Neuro-ophthalmologic examination revealed abducting hypertropia on lateral gaze, better seen during upgaze, mimicking bilateral inferior oblique palsy (video, figure ”there is no video”). There was no ocular cyclotorsion. Brain MRI revealed focal ischemic lesions in the right cerebellar hemisphere and left superior colliculus (figure). The diagnosis of alternating abducting hypertropic skew deviation was made. This rare type of skew deviation is related to central otolithic dysfunction. Similar cases have been described with cerebellar, pretectal, or cervico-medullary junction lesions. Orthoptic management can help and patients can slowly improve over months.”1

Alternating Skew on Lateral Gaze : Neuroanatomic Pathway and Relationship to Superior Oblique Overaction. Hamed LM, et al. Ophthalmology 1993:100:2:281–286
Abstract
Background: Previous studies of patients with heterogeneous, often diffuse neurologic disorders concluded that the neurologic substrate for alternating skew on lateral gaze may be localized at the level of the brain stem tegmentum or the cervico-medullary junction, or both. The localized nature of brain tumors offers an opportunity to further investigate the anatomic localization for this as well as other conditions.
Methods: To test the hypothesis that cervico-medullary and cerebellar lesions are responsible for alternating skew on lateral gaze, the authors investigated a series of 50 children with brain tumors, 39 of whom showed neuro-ophthalmologic abnormalities on clinical testing. Seven children had alternating skew on lateral gaze.
Results: All seven children with alternating skew on lateral gaze showed neoplastic involvement at the level of the cervico-medullary junction and/or the cerebellum on critical analysis of neuro-imaging studies.
Conclusion: The authors conclude that the neuroanatomic substrate for alternating skew on lateral gaze is localized at the level of the cervico-medullary junction and/or the cerebellum. Knowing that (1) alternating skew on lateral gaze closely mimics superior oblique overaction clinically, (2) superior oblique overaction is frequently found in patients with myelomeningocele, and (3) myelomeningocele is uniformly associated with Arnold Chiari type II which includes cerebellar and cervico-medullary region abnormalities, the authors propose that alternating skew on lateral gaze and superior oblique overaction associated with myelomeningocele have similar neuroanatomic pathways.”2

“Skew deviation is a vertical strabismus caused by a supranuclear lesion, commonly in the brainstem or cerebellum… It is associated with abnormal utriculo-ocular reflexes, as evidenced by: (1) asymmetric reduction in translational vestibulo-ocular reflex responses; (2) asymmetric reduction in the ocular counter roll reflex responses; and (3) head position-dependent changes in torsion and vertical misalignment. Understanding the anatomy and physiology of the central otolithic pathway not only allows us to gain insight into the pathophysiologic mechanism of skew deviation, it also allows us to devise a new clinical test to differentiate skew deviation from fourth nerve palsy and other causes of vertical strabismus.”3

References:
1. Teaching Video NeuroImages: Alternating skew deviation with abducting hypertropia following superior colliculus infarction. Biotti D, et al. Neurology:2016:86:9:e93 -e94
2. Alternating Skew on Lateral Gaze : Neuroanatomic Pathway and Relationship to Superior Oblique Overaction. Hamed LM, et al. Ophthalmology 1993:100:2:281–286
3. New understanding on the contribution of the central otolithic system to eye movement and skew deviation. Wong AMF. Eye (Lond). 2015;29(2):153–156.

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