Episodic exotropia from lateral rectus neuromyotonia--appearance and remission after radiation therapy for a thalamic glioma.

Sixteen months after radiation therapy for a moderately anaplastic astrocytoma of the thalamus, a 7-year-old boy developed spontaneous episodic contractions in his left lateral rectus muscle. During these episodes, lasting 10 to 30 seconds and occurring 20 or more times a day, he had exotropia, limitation of adduction, and retraction of the left globe. This phenomenon peaked in duration and frequency at 14 months and gradually disappeared after 22 months. As this case confirms, radiation injury to the abducens nerve can cause ocular neuromyotonia, resulting in episodic strabismus. Our case also illustrates that this condition can disappear completely after many months.