- 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)
- 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)
- Multiple sclerosis (most common cause in young patients)
- Malignancy located in brainstem and 4th ventricle
- CN III palsy
- Evaluate for underlying cause based on clinical presentation
- The use of optokinetic tape is highly sensitive for testing for INO
- 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
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.