Ocular neuromyotonia is a rare, albeit treatable, ocular motor disorder, characterised by recurrent brief episodes of diplopia due to tonic extraocular muscle contraction. Ephaptic transmission in a chronically damaged ocular motor nerve is the possible underlying mechanism. It usually improves with carbamazepine. A 53-year-old woman presented with a 4-month history of recurrent episodes of binocular vertical diplopia (up to 40/day), either spontaneously or after sustained downward gaze. Between episodes she had a mild left fourth nerve palsy. Sustained downward gaze consistently triggered downward left eye tonic deviation, lasting around 1 min. MR scan of the brain was normal. She improved on starting carbamazepine but developed a rash that necessitated stopping the drug. Switching to lacosamide controlled her symptoms.
- ocular neuromyotonia
- trochear nerve
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RS--R and AIM contributed equally.
Contributors All authors were responsible for the clinical care of the patient. The initial draft was written by RSR and AIM. AIM and JL recorded the patient video. All authors reviewed and contributed to the final manuscript.
Competing interests None declared.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed. This paper was reviewed by Mark Lawden, Leicester, UK.