[Case of ocular neuromyotonia with transient and gaze-induced diplopia].

A 71-year-old man had recurrent spells of transient diplopia for about four years. Vertical diplopia were induced by downward gaze, mostly to the lower-left, and lasted for about ten seconds. During the spells, limitation in elevation of the left eye was observed. Other neurological examinations were normal except for a minor paresis of the left trochlear nerve revealed only by detailed neuroophthalmological examination. The patient was treated with carbamazepine 200 mg daily, which abolished the spells. He was diagnosed to have idiopathic ocular neuromyotonia of the left third or fourth nerve. Ocular neuromyotonia is a rare disturbance of ocular motility, characterized by paroxysmal monocular involuntary spasms of one or more extraocular muscles supplied by the third, fourth or sixth cranial nerves. Past studies showed that most patients had radiation therapy to the parasellar or sellar regions. Slight injury to the peripheral nerves such as one caused by radiation may have an important role in the development of ocular neuromyotonia. Furthermore, patients with ocular neuromyotonia often benefit from the use of carbamazepine, a membrane-stabilizing agent. We report a case of idiopathic ocular neuromyotonia without history of damage to the cranial nerves. It is the first report in Japan.