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


Disposition



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.

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