Internuclear ophthalmoplegia

Background

• Focal neuro deficit caused by injury or dysfunction of medial longitudinal fasciculus
• Paramedian Pontine Reticular Formation (PPRF) is the conjugate gaze center for horizontal eye movements. Innervates ipsilateral Abducens (CN VI) nucleus. Abducens nucleus signals ipsilateral lateral rectus to contract and sends a second via MLF to contralateral oculomotor (CN III) nucleus, causing contraction on the contralateral medial rectus.
• Associated with one and one-half syndrome (lesion involving the PPRF and ipsilateral MLF)

Clinical Features

Schematic of right internuclear ophthalmoplegia caused by injury to right medial longitudinal fasciculus

• Impaired adduction when attempted to gaze contralaterally to affected eye
• Contralateral eye abducts with nystagmus
• Divergence of eyes results in horizontal diplopia when looking contralateral (to affected eye)
• Convergence remains intact (differentiates CN III palsy from INO)

Differential Diagnosis

• Multiple sclerosis (most common cause in young patients)
• Stroke
• Malignancy located in brainstem and 4th ventricle
• CN III palsy would show additional deficit including weakness of elevation, ptosis, pupil dilation

Evaluation

• Evaluate for underlying cause based on clinical presentation
• The use of optokinetic tape is highly sensitive for testing for INO
• MRI

Management

• Treat underlying condition
• Symptoms will often resolve on their own. Patients with cerebrovascular disease are less likely to have recovery.
• Patching of eye can aid in relief of diplopia
• Diframpadine, potassium channel blocker, has been used in patients with demyelinating disease

References

Ropper A, Klein J, Samuels M. Adams and Victor's Principles of Neurology 10th Edition. McGraw-Hill Education / Medical; 2014.

Serra A, Skelly MM, Jacobs JB, et al. Improvement of internuclear ophthalmoparesis in multiple sclerosis with dalfampridine. Neurology 2014; 83:192.