Strabismus Surgery in Patients With Ocular Neuromyotonia: Potential Unmasking of the Condition and Effective Management Tool

Abstract

Background Ocular neuromyotonia is a rare motility disorder in which paroxysms of tonic extraocular muscle contraction from abnormal ocular motor nerve firing result in episodic diplopia and strabismus. Medical therapy with membrane-stabilizing agents has varied success. A surgical approach to treatment has not yet been described. We report the outcomes of strabismus surgery in patients with ocular neuromyotonia. Methods We describe three patients with sixth nerve paresis and ocular neuromyotonia of the affected lateral rectus muscle who underwent strabismus surgery. All patients had a history of radiation therapy for intracranial tumors. Ophthalmologic and orthoptic examinations were performed with appropriate medical and neuroradiologic evaluation. Pre-operative and post-operative data are presented and analyzed. Results Two patients were noted to have ocular neuromyotonia after their first strabismus surgery for a sixth nerve palsy. Patients 1 and 2 had three surgeries while patient 3 had one operation. Extraocular muscles operated on included the medial rectus and lateral rectus. Pre-operative primary gaze baseline esotropia ranged from 35 to 75 prism diopters (Δ). All patients achieved improvement in ocular alignment and motility. Post-operative primary gaze deviations ranged from orthotropia to 20Δ of esotropia. Abduction deficits were unchanged or improved. The follow-up period ranged from 15 months to 2 years. Conclusions Patients with ocular neuromyotonia of a paretic rectus muscle can achieve binocular fusion with strabismus surgery. Ocular neuromyotonia may manifest post-operatively in patients with a sixth nerve palsy and a contractured medial rectus who, pre-operatively, were not noted to have ocular neuromyotonia.

Conversion of Superior Oblique Myokymia to Superior Oblique Neuromyotonia in a Patient With History of Superior Oblique Palsy

“…In addition, it is worth noting that the patient's symptoms manifested after strabismus surgery, a phenomenon that has been reported before by Kim et al . 4 In their case series, 2 patients had medial rectus recession and lateral rectus resection before the onset of CN VI ONM. One theory to explain this observation is that ONM is initially masked preoperatively because of restriction by the antagonist muscle that prevents ocular rotation.…”

Ocular neuromyotonia: a review of diagnosis and treatment

“…Surgical management can be an option after medical therapy. Strabismus surgery has been described for correction of ocular misalignment in ONM yet some cases of ONM occur after strabismus surgery for prior ocular disease [2 ▪▪ ,56]. Kim et al reported two patients with ONM after initial strabismus surgery and one patient with ONM following radiotherapy that underwent strabismus surgery for ocular misalignment, with subsequent resolution of their ONM [56].…”

“…Strabismus surgery has been described for correction of ocular misalignment in ONM yet some cases of ONM occur after strabismus surgery for prior ocular disease [2 ▪▪ ,56]. Kim et al reported two patients with ONM after initial strabismus surgery and one patient with ONM following radiotherapy that underwent strabismus surgery for ocular misalignment, with subsequent resolution of their ONM [56]. Reviewing seven cases of resolved ONM following recession of the neuromyotonic muscle, they hypothesize that reducing the resting tension by weakening the neuromyotonic muscle may help mitigate spasms [56].…”

“…Kim et al reported two patients with ONM after initial strabismus surgery and one patient with ONM following radiotherapy that underwent strabismus surgery for ocular misalignment, with subsequent resolution of their ONM [56]. Reviewing seven cases of resolved ONM following recession of the neuromyotonic muscle, they hypothesize that reducing the resting tension by weakening the neuromyotonic muscle may help mitigate spasms [56]. In cases of ONM due to nerve compression, neurosurgical microvascular decompression can achieve resolution of symptoms.…”