Ocular Neuromyotonia Noted after Recent Botulinum Toxin Injection for Sixth Nerve Palsy Following Resection of a Posterior Fossa Skull Base Meningioma

摘要

A 56-year-old female complained of diplopia immediately after surgical excision of a recurrent left skull base tuberculum meningioma. She was found to have a left sixth nerve palsy, which was subsequently treated with botulinum toxin injection to the medial rectus muscle. Three months post injection, the patient had partial recovery of the sixth nerve palsy and new-onset ocular neuromyotonia. Ocular neuromyotonia (ONM) is a rare paroxysmal neuromuscular disorder characterised by involuntary contraction of extraocular muscles. ONM is usually accompanied by episodic diplopia and variable angle strabismus. Reported causes include prior radiation treatment, chronic cranial nerve palsy affecting ocular motility, thyroid-related orbitopathy, compressive lesions, or stroke. There have even been a few reported cases that are idiopathic in origin. The precise pathophysiology of the disorder is unknown, but is thought to be related to axonal instability. Hence, membrane-stabilising agents such as carba-mazepine and gabapentin have been utilised for treatment. Currently, sparse literature exists describing the relationship to prior cranial nerve palsies affecting ocular motility or the potential association with botulinum toxin. We present a patient with ONM that developed after botulinum toxin was utilised in the treatment of a sixth nerve palsy that occurred immediately after neurosurgery for resection of a recurrent meningioma with a history of prior radiation therapy.