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A 25-year-old woman was referred to the neuro-ophthalmology clinic because of a 6-month history of intermittent diplopia. The double vision occurred every day, multiple times throughout the day, and was provoked after looking to the right. There was no eye pain, headache, ptosis, difficulties swallowing, change in voice, or any other ocular or neurological symptoms.
She had no history of strabismus, eye patching, or ocular surgery. Her medical history was notable for a growth hormone–producing pituitary macroadenoma for which she underwent surgical resection 2.5 years prior to presentation, followed by γ-knife radiosurgery (50 Gy) 6 months after the initial surgical procedure. She also had a history of congenital hip dysplasia. Medications included cabergoline, levothyroxine, ethinyl estradiol/drospirenone, and pasireotide.
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Right sixth-nerve ocular neuromyotonia
A. Initiate a trial of carbamazepine
The differential diagnosis of intermittent double vision owing to an exodeviation is limited and includes third-nerve palsy, internuclear ophthalmoplegia, myasthenia gravis, orbital disease (such as myositis, tumor, or trauma), intermittent exotropia, and ocular neuromyotonia.1 In this patient, the findings on voluntary eye movements provided valuable information and narrowed the diagnosis to only 1 entity, a right sixth-nerve ocular neuromyotonia. Intermittent exotropia alone can occur from any of the entities mentioned, but only in a case of ocular neuromyotonia will there be an intermittent ocular misalignment after prolonged activity of the extraocular muscle innervated by the affected ocular motor cranial nerve. Symptomatic ocular neuromyotonia is treated medically, with the first-line treatment being carbamazepine (choice A), a voltage-gated sodium-channel blocker.2,3 Bilateral lateral rectus recessions (choice B) is not indicated for ocular neuromyotonia. Although most cases of acquired diplopia in a young person warrant neuroimaging, the history of γ-knife radiosurgery and eye movement findings consistent with ocular neuromyotonia obviated the need for a magnetic resonance imaging study (choice C). Checking anti-acetylcholine receptor binding antibodies (choice D) is not necessary, because myasthenia gravis does not cause an ocular deviation and limitation of eye movements after prolonged activity of a particular extraocular muscle.
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Corresponding Author: M. Tariq Bhatti, MD, Department of Ophthalmology, Mayo Clinic, 200 First St SE, Rochester, MN 55905 (firstname.lastname@example.org).
Published Online: May 2, 2019. doi:10.1001/jamaophthalmol.2019.1091
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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