Disorders• 8 SECTIONMotor Ocular Brainstem

Internuclear Ophthalmoplegia

Key Facts

•Adduction weakness caused by interruption of neural transmission within medial longitudinal fasciculus

•Jerk nystagmus of abducting fellow eye often present

•Vertical misalignment (skew deviation) often present

•Saccadic pursuit, ipsilateral gaze palsy (one and a half syndrome), and ataxia may occur

•Lesion lies in cerebellum, pons, or midbrain

•Common causes:

•ischemic stroke in older adults

•multiple sclerosis in younger adults or children

•Other causes:

•head trauma

•brainstem or cerebellar tumor or hemorrhage

•neurodegenerative, toxic, or metabolic disorders

Clinical Findings

•Deficit ranges from adduction slowing (with full adduction) to absent adduction

•Jerk nystagmus in abduction of fellow eye is common but not obligatory

•Eyes may be aligned in primary position or show exodeviation

•Vertical misalignment (skew deviation) is common

•Saccadic pursuit is common

•Eye findings may be accompanied by ataxia or extremity weakness and numbness

Ancillary Testing

•Brain imaging may be normal if the cause is brainstem ischemic stroke, demyelination, or other inflammation, toxic, or metabolic disorders

•Brain MRI readily identifies brainstem or cerebellar tumors or hemorrhages

Differential Diagnosis

•Myasthenia gravis

•Third cranial nerve palsy

•Orbital myositis

•Traumatic orbitopathy

•Orbital tumor

Treatment

•Because eyes are often aligned in primary position, diplopia is usually not debilitating

•For primary position misalignment, extraocular muscle surgery can be performed if condition is stable for at least 1 year

Prognosis

•Often remits if caused by acute demyelination

•Sometimes remits if caused by brainstem stroke (depending on severity)

•Surgical realignment often successful in palliating primary gaze diplopia

Disorders• 8 SECTIONMotor Ocular Brainstem

Skew Deviation

Key Facts

•Vertical misalignment caused by unilateral (or bilaterally asymmetric) interruption of neural connections between semicircular canals and ocular motor nuclei

•Misalignment may be comitant or incomitant

•Saccadic pursuit, nystagmus, internuclear ophthalmoplegia, gaze paresis, or ataxia often present

•Lesion usually lies in brainstem but may rarely be in semicircular canals or vestibular nerve

•Common causes:

•brainstem ischemic or hemorrhagic stroke

•brainstem or cerebellar tumor

•multiple sclerosis

•Other causes: neurodegenerative, infectious, and toxic or metabolic disorders

Clinical Findings

•Vertical misalignment that may be comitant or incomitant

•Can usually be distinguished from fourth cranial nerve palsy by lack of positivity on three-step test and lack of excyclotorsion on double Maddox rod test

•Other signs often present:

•saccadic pursuit

•nystagmus

•internuclear ophthalmoplegia

•gaze paresis

•limb, gait, or speech ataxia

Ancillary Testing

•MRI readily identifies brainstem or cerebellar tumors or hemorrhages but may be normal in brainstem stroke, demyelination, or other inflammation

Differential Diagnosis

•Third cranial nerve palsy

•Fourth cranial nerve palsy

•Myasthenia gravis

•Orbital myositis

•Graves disease

•Traumatic orbitopathy

•Orbital tumor

Treatment

•May be able to eliminate diplopia with a Fresnel or ground-in spectacle prism

•In unremitting skew deviation, extraocular muscle surgery is an option

Prognosis

•Skew deviation may spontaneously remit if brainstem lesion is demyelinative or otherwise mild

•Extraocular muscle surgery may fail to provide an adequate zone of single binocular vision if patient lacks fusional ability

Fig. 8.3 Skew deviation. In all gaze positions, the right eye is higher than the left eye (right hypertropia). In skew deviation, the eyes are always vertically

misaligned. The degree of misalignment may be the same (comitant) or different (incomitant) as gaze positions change.

Fig. 8.4 Skew deviation in pontine glioma. Axial FLAIR MRI shows diffuse high signal in the pons (arrow).

Deviation Skew