Resident Pearl by Dr. Saly Halawa
iFMEM PGY2
Dalhousie University
Reviewed by Dr. B Ramrattan
Copy Edited by Dr. J Vonkeman
Pdf Download: EMSJ Bilateral INO SHalawa
Case Presentation
A 42yo male presents to the Emergency Department with abrupt onset right-sided facial numbness and double vision. His facial numbness quickly improved but he continued to have diplopia and gait ataxia. He denied headache, nausea or photophonophobia. The patient had a history of sickle cell disease and diabetes. His medications included hydroxyurea and insulin. On physical examination, he was unable to adduct his eyes bilaterally on lateral gaze with abducting nystagmus. His power, tone, reflex, and sensation were all normal.
Internuclear Ophthalmoplegia (INO)
Internuclear ophthalmoplegia (INO) is a neurologic condition characterized by impaired control of conjugate eye movements (1). It is caused by a lesion of the medial longitudinal fasciculus (MLF) in the brainstem. The MLF is the pathway containing internuclear neurons connecting cranial nerve nuclei that control conjugate eye movements. These include the nucleus of the abducens nerve (CN VI) in the pons and the contralateral nucleus of the oculomotor nerve (CN III) in the midbrain supplying the medial rectus (1). Together CNIII and CN VI allow for adduction and abduction of the eye, respectively. For instance, interneurons of CNVI on one side project across the midline to the contralateral MLF which ascends to CNIII to control the medial rectus on that side, allowing the lateral and medial rectus to move the eyes together (1). In this way, the MLF coordinates eye movements between both eyes allowing for conjugate gaze. Patients with INO have an adduction deficit on the ipsilateral side with associated contralateral nystagmus of the abducting eye.
INO is named with respect to the side of the adduction deficit, which is the side of the MLF lesion. A R sided INO is due to a lesion of the R MLF. Patients may also present with bilateral INO as in the case presented here.
Figure 1: Adduction Defects produced by Internuclear Ophthalmoplegia (1)
Patients with INO often experience horizontal diplopia due to dysconjugate gaze or they may report vertical-oblique diplopia due to associated skew deviation (1). Patients may also present with difficulty in tracking fast-moving objects as a result of a mismatch in saccadic movements between the eyes.
Differential
The differential diagnosis for INO is broad (1). The most common causes of bilateral INO include multiple sclerosis in younger patients, often younger than 50 yrs old, or due to brainstem infarction in older patients. Other causes of INO include infection, toxicity to medications including amitriptyline, benzodiazepines or ethanol, chiari malformations or trauma. In the present case, bilateral INO was the first presentation of MS due to demyelination of the MLF.
Prognosis
Prognostically, INO symptoms do improve over time, often resolving spontaneously after an average of 2 months, but up to 12 months (2). Associated neurologic symptoms such as vertigo, ataxia, sensory or speech deficits are poor prognosticating factors. Those with cerebrovascular etiology have less favorable recovery as well.
Figure 2: Internuclear Ophthalmoplegia caused by lesion at the Medial Longitudinal Fasciculus (4)
Video link: https://www.youtube.com/watch?v=eL3_6yYJdUA&ab_channel=MoranCORE
Case Conclusion
CT angiography of the brain demonstrated no evidence of acute infarction. MRI showed periventricular white matter hyperintensities which was also seen in the corpus callosum, suspicious for multiple sclerosis. He was given a five-day trial of methylprednisolone.
Bottom Line
Though uncommon, internuclear ophthalmoplegia points to a brainstem lesion with a wide variety of causes. Multiple sclerosis should be suspected in a young patient presenting with bilateral INO.
References
- Toral M, Haugsdal J, Wall M. Internuclear Ophthalmoplegia. EyeRounds.org. posted June 8, 2017; Available from: http://EyeRounds.org/cases/252-internuclear-ophthalmoplegia.htm
- Eggenberger E, et al. Prognosis of ischemic internuclear ophthalmoplegia. Ophthalmology. 2002; 109(9):1676-8.
- https://www.youtube.com/watch?v=eL3_6yYJdUA&ab_channel=MoranCORE
- https://sketchymedicine.com/2013/12/internuclear-opthalmoplegia/
