Timothy C. Hain, MD• Page last modified: April 28, 2020
Internuclear opthalmoplegia is classically found in persons with Multiple Sclerosis. While there are other causes, this is by far the most common cause. On the other hand, while many persons with dizziness are very anxious about having MS, practically it is very uncommon to diagnose MS in a person with vertigo or unsteadiness. The reason for this is that MS is an uncommon disease, far less common than inner ear conditions such as BPPV, or common neurological disorders such as migraine.
When an INO is found, it is good evidence for a brainstem disorder. As brainstem disorders commonly cause dizziness, this means that failing other positive findings, in a person with MS, the cause of the dizziness in that person is most likely disruption of brainstem pathways.
A woman in her late 50's was referred for chronic dizziness. She has well known MS.
Exam showed slurred and "scanning" speech, unsteadiness, and prominent internuclear ophthalmoplegia. When she looked to either side, the inward going eye would be slow, while the outward going eye very fast.
In the recording above, the person is asked to track a dot that moves back and forth on a screen. The eyes are plotted on top of each other. Often one eye goes too far and drifts back, while the other moves more slowly onto the target. The eye that overshoots is the right eye (when looking to the right), and the left eye (when looking to the left). This is a classic appearence to a bilateral INO.
A woman with progressive unsteadiness, had previously been diagnosed with MS. On her examination, she had a very obvious bilateral INO. She was sent for another MRI scan. The saggital views show "Dawson's fingers", projecting from the edges of the lateral ventricle. Nothing was seen in the brainstem, perhaps because this was an Open Mri (and therefore low resolution).
Pursuit and saccadic tracking in patient with bilateral INO. Note that eye tracking is disconjugate. Images courtesy of Dr. Dario Yacovino.