Walsh & Hoyt: Ocular Neuromyotonia

This is an acquired condition in which various eye muscles go into brief intermittent spasm, causing diplopia that comes and goes. Usually the muscles relate to one ocular motor nerve, but they may relate to more than one or be bilateral. Sometimes only one muscle, such as the levator palpebrae superioris, is involved. Occasionally the condition is self-limited. Most patients had undergone radiation therapy for brain tumors or pituitary tumors months to years before. The history of radiation is not always obvious. One 72-year-old man developed ocular neuromyotonia after having undergone myelography many years earlier using thorium dioxide (Thorotrast), a substance that is weakly radioactive and that remained in his subarachnoid space. Ocular neuromyotonia can develop without radiation injury in patients with Graves dysthyroid orbitopathy, internal carotid aneurysm, compression of the oculomotor nerve by a dolichoectatic basilar artery, or months after cavernous sinus thrombosis from mucormycosis. It is unclear whether ocular neuromyotonia is related to the delayed myotonia of limb muscles that can follow radiation to the brachial plexus.