Dataset Information

Bilateral oculomotor ocular neuromyotonia: a case report.

ABSTRACT:

Background

Ocular neuromyotonia (ONM) is characterized by episodic diplopia, which is usually triggered by prolonged eccentric gaze of the affected extraocular muscles. The spell is characterized by involuntary, occasionally painful, sustained contraction of one or more extraocular muscles innervated by the oculomotor, trochlear, or abducens nerve. ONM usually occurs as a late consequence of radiotherapy around the parasellar area, although idiopathic cases have been reported. Most cases are unilateral; however, bilateral ONM has occasionally been described.

Case presentation

A 60-year-old woman presented with a 4-month history of episodic, painful, horizontal binocular diplopia. She underwent external beam radiotherapy to the skull base for treatment of nasopharyngeal carcinoma. The tumor was well controlled. General neurological examination findings were unremarkable. Neuro-ophthalmic examination revealed normal visual acuity, visual fields, pupils, and fundi. Ocular alignment showed orthotropia with normal ocular motility. Myasthenic eyelid signs were absent. However, she developed episodes of involuntary sustained contraction of the medial rectus muscle following prolonged eccentric gaze toward the affected medial rectus muscle, which resulted in esotropia upon returning to the primary position. The esotropic episodes spontaneously resolved after approximately 2 min. These spells affected both medial rectus muscles. Both pupils remained normal throughout the examination. Magnetic resonance imaging revealed neither brain parenchyma/brain stem lesions nor tumor recurrence. Her symptoms were successfully treated with carbamazepine.

Conclusions

Episodic esotropia in the adducting eye following prolonged horizontal eccentric gaze is a significant characteristic of ONM affecting the bilateral medial rectus muscles (i.e., bilateral oculomotor ONM). In spite of its extreme rarity, ONM should be considered as a differential diagnosis of episodic diplopia, especially in patients with a history of radiotherapy around the parasellar area. Careful examination with prolonged eccentric gaze should be performed to achieve a correct diagnosis and avoid an extensive unnecessary workup.

SUBMITTER: Padungkiatsagul T

PROVIDER: S-EPMC6120096 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:RationaleAcquired neuromyotonia syndrome is a rare form of peripheral nerve hyperexcitability syndrome. It is characterized by spontaneous and continuous muscle contractions. Acquired neuromyotonia syndrome is mainly observed in patients with autoimmune diseases or tumors, but it is a rare neurological clinical manifestation in patients with mercury poisoning.Patient concernsA 56-year-old woman presented with continuous and involuntary muscle twitching in her legs for 2 months; it was accompanied by a burning sensation in the lower limbs, insomnia, fatigue, and night sweats. These symptoms did not disappear during sleep.DiagnosesToxicological blood analysis via atomic fluorescence spectrometry revealed that the level of mercury was 0.07 μmol/L (normal level: <0.05 μmol/L). Her urinary mercury level measured using the cold atomic absorption method was 217.50 μmol/mol creatinine, which was considerably higher than the reference range (0-2.25 μmol/mol creatinine for people not in contact with mercury, 0-20 μmol/mol creatinine following long-term exposure). Upon further testing, a high level of mercury (10,572 mg/kg) was detected in the patient's cream. Accordingly, this patient was diagnosed with mercury poisoning.InterventionsTreatment with 2,3-dimercapto-1-propanesulfonic acid (DMPS) was initiated. Her urinary mercury level decreased to 9.67 μmol/mol creatinine, and her neuromyotonia syndrome and hyponatremia were relieved, with urine protein completely disappearing after 3 months of treatment.OutcomesAfter DMPS treatment, the clinical manifestations of the nervous system disappeared and electrolyte parameters returned to normal levels.LessonsAcquired neuromyotonia syndrome is a rare disorder caused by the hyperexcitability of peripheral nerves, resulting in spontaneous and continuous muscle contraction. Mercury poisoning should be considered in patients with neuromyotonia syndrome. Early detection of mercury poisoning can prevent unnecessary examinations and treatments.