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Emily C. Taylor, Natalie C. Kerr; Ocular Neuromyotonia in Congenital Third Nerve Palsy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3888.
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Ocular neuromyotonia is a rare disorder characterized by an episodic misalignment of the eyes which may occur spontaneously or following a period of eccentric gaze. It is most commonly seen following radiation to the sellar region of the brain, but cases associated with compressive lesions, alcohol abuse, and vascular anomalies have been reported. We present a case of ocular neuromyotonia in a patient with congenital third nerve palsy without any other neurologic pathology.
A 2-year-old patient with otherwise unremarkable past medical history was referred to the pediatric ophthalmology clinic for evaluation of abnormal ocular motility. On initial examination she was found to have esotropia or exotropia at different times of the examination. Eventually, a congenital right third nerve palsy was recognized in association with a right esotropia after prolonged left gaze. Magnetic resonance imaging of the brain and associated vasculature was obtained and was noted to be normal.
The patient demonstrated 25 prism diopters of exotropia in primary gaze. Abduction of the right eye was normal, but adduction, elevation, and depression were limited on duction and version testing. After prolonged left lateral gaze, the patient demonstrated a reproducible right esotropia of 60 prism diopters which lasted several seconds. The patient demonstrated inability to abduct the right eye during this paroxysmal misalignment. The patient was started on carbamazepine with resolution of this paroxysmal motility disturbance. During periods of non-compliance with drug use, the episodic esotropia would return. Eventually the patient underwent a recess-resect procedure of the right eye to correct the exotropia associated with the third nerve palsy.
Ocular neuromyotonia is a well described disorder which typically follows a previous neurologic insult. The mechanism is not fully understood, but electromyographic activity of the involved extraocular muscle suggests that cell membrane instability of the ocular motor nerve axons results in spontaneous discharges which cause paroxysmal contraction of the muscle. The resolution of symptoms with carbamazepine, which stabilizes neuronal cell membranes, supports this hypothesis. This patient demonstrates the first reported case of ocular neuromyotonia in congenital nerve palsy and underlines the need for further elucidation of the pathogenesis of the disorder.
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