Midbrain-Thalamic Ocular Neuromyotonia

Ocular neuromyotonia is characterized by paroxysms of tonic contraction of 1 or more of the extraocular muscles, usually consequent to radiation.^1,2 We describe a unique example of ocular neuromyotonia from nonirradiated, stroke-related intramedullary lesions of the midbrain and thalamus.

A healthy 41-year-old man lapsed into a coma after developing sudden dizziness, sweating, and diplopia. Magnetic resonance imaging (Figure) showed high signal intensity on T2-weighted images at the left mesodiencephalic junction involving the left red nucleus and third nerve extending superiorly to the left centromedian thalamus, a punctate focus of susceptibility at the root exit zone of the left third nerve and a small area of abnormal signal at the right mesodiencephalic junction. The lesions were consistent with hemorrhage and infarction. The patient was presumed to have suffered a stroke. He improved but had residual diplopia, a “clumsy” right arm, and gait ataxia.

Three months after the onset, there was bilateral lid retraction, slow elevation and depression of both eyes, and limited elevation and depression of the left eye. His pupils were unremarkable. Two days later, the patient reported that he had developed about 30 episodes daily of vertical diplopia, each heralded by transient right periorbital tingling. His right eye would deviate down and in for up to 3 minutes. Tingling would recur, and the eye would return to a normal position. There was no oscillopsia. Observation of several episodes during re-examination several days later confirmed his description. Carbamazepine abolished the episodes. Three months later, he had full ductions, but elevation and depression of both eyes were slow. On all refixations, both eyes would make a slow, conjugate, small-amplitude clockwise rotation and then a corrective movement before stabilizing. At present, he is still receiving carbamazepine.

Ocular neuromyotonia affects the extraocular muscles either individually or in combination, causing episodic diplopia that develops either spontaneously or after gaze in the direction of action of the affected muscle. Electromyography suggests a neurogenic basis for the movements.^3,4 The tonic contractions are thought to result from the spontaneous discharge of unstable neurons, which are transmitted to adjacent neurons by ephaptic transmission. Consistent with the theory of axonal instability, membrane-stabilizing agents such as carbamazepine are effective.

To our knowledge, this is the first report of a patient whose ocular neuromyotonia was caused by a stroke, as well as the first in which the responsible lesion was intramedullary. Our patient’s lesions were predominantly contralateral to the side of his neuromyotonia, with only 1 small lesion at the ipsilateral mesodiencephalic junction. While we cannot determine which, if any, of his lesions caused the neuromyotonia of his right eye, we note that his lesions spared the nuclei and intramedullary fascicles of the right third nerve. We conclude that ocular neuromyotonia can result from purely intramedullary lesions, without the involvement of the lower motor neuron.

Correspondence: Dr Lessell, Massachusetts Eye and Ear Infirmary, 243 Charles St, Boston, MA 02114 (simmons_lessell@meei.harvard.edu).

Financial Disclosure: None.

Funding/Support: Manuscript development was supported in part by grant G12-RR03026-15 from the National Center for Research Resources, Bethesda, Md.