The most common causes of an INO are MS and brainstem stroke.(3,5,6) INOs due to MS are usually bilateral and seen in young patients; those due to brainstem vascular disease are more often unilateral and seen in older patients. About 25% are due to unusual causes such as trauma or tumor.(4) This patient has INOs bilaterally, worse on the right. On left gaze, adduction of the right eye is severely limited and there is nystagmus in the left eye. MRI showed multiple areas of demyelination, including a lesion in the right MLF.
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2. Campbell WW. DeJong's the neurologic examination, 7th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2013.
3. Hassen GW, Bhardwaj N. Images in clinical medicine. Bilateral internuclear ophthalmoplegia in multiple sclerosis. N Engl J Med. 2013 Jan 17;368(3):e3.
4. Keane, JR. Internuclear ophthalmoplegia: unusual causes in 114 of 410 patients. Arch Neurol. 2005; 62:714-717.
5. McNulty JP, Lonergan R, Bannigan J, O'Laoide R, et al. Visualisation of the medial longitudinal fasciculus using fibre tractography in multiple sclerosis patients with internuclear ophthalmoplegia. Ir J Med Sci. 2016 May;185(2):393-402.
6. Saini M, Bte Idu Jion Y. Periprocedural stroke presenting as isolated unilateral internuclear ophthalmoplegia. QJM. 2015 Feb;108(2):165.