Internuclear Ophthalmoplegia (INO) in multiple sclerosis

This video includes 3 patients each with a known history of MS found to have unilateral or bilateral INOs on their exam. In the first 2 patients, the INOs are relatively subtle with normal adduction. However, with rapid horizontal saccades, an adduction lag is apparent which is suggestive of an INO. Occasionally a pseudo-INO can be seen in the setting of myasthenia, due to relative medial rectus weakness that exacerbates with repeated horizontal saccades (i.e., it fatigues). Because some of the fibers responsible for vertical gaze holding travel through the MLF, upbeat nystagmus in upgaze is common with bilateral MLF lesions. Number of Videos and legend for each: 1, This video shows 3 patients with MS and INOs.