Case of Facial Neuromyotonia

Clinical Correspondence Section Editors: Robert Avery, DO Karl C. Golnik, MD Case of Facial Neuromyotonia Caleb Z. Rivera, BS, Alexander M. Solomon, MD, Courtney E. Francis, MD A Downloaded from http://journals.lww.com/jneuro-ophthalmology by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC4/OAVpDDa8K2+Ya6H515kE= on 05/04/2022 76-year-old woman was referred to the neuroophthalmology clinic for evaluation and treatment of left facial spasms. Her medical history was significant for a left acoustic schwannoma diagnosed 4 years prior when she presented with progressive hearing loss and balance difficulties, and an MRI demonstrated an enhancing extra axial mass at the left cerebellopontine angle extending into the left internal auditory canal (Fig. 1). The mass was presumptively treated with Leksell gamma knife radiation consisting of 13 Gy to the 50% isodose surface. Her post-treatment course was complicated by communicating hydrocephalus requiring placement of a Codman ventriculoperitoneal shunt 2.5 years later. Five months before presentation to our clinic, and approximately 3 years after radiation, she presented to an emergency department with left facial drooping and prolonged closure and inability to open her left eye. Stroke workup including an MRI was negative other than a stable left cerebellopontine angle mass, and she was started on levetiracetam for presumed partial seizures without improvement in her symptoms. The frequency of her spasms was variable, ranging from multiple episodes a day to several days between symptoms. Initially, these contractions would last seconds, but over time, the duration progressed to minutes. She described the episodes as constant contractions of her left face that gradually self-resolved without associated pain (Fig. 2). She was unable to identify any aggravating factors but noted episodes occurred most typically shortly after awakening in the morning. On examination, visual acuity was 20/30 in the right eye and 20/20 in the left eye. Pupillary examination and color plate testing were normal in both eyes, and optic nerves were without edema or atrophy. She was noted to have mild left nasolabial flattening without associated weakness, intact sensation in V1-V3 distributions bilaterally, fluent speech, and chronic left sensorineural hearing loss. Given the duration of her contractions during episodes, a diagnosis of facial neuromyotonia rather than hemifacial spasms or partial seizures was made. The neuromyotonia was attributed to post-radiation changes after gamma knife treatment of her acoustic neuroma, which was intimately close to the facial nerve. She was started on carbamazepine 100 mg twice daily and subsequently had complete resolution of symptoms. Neuromyotonia is believed to originate in motor axon segments and results from spontaneous depolarization of demyelinated nerves, which leads to persistent contraction of affected muscles. This is often caused by radiation inducing damage directly to nerves or nearby vasculature resulting in ischemic insults with secondary injury and fibrosis (1). Ocular neuromyotonia has most commonly been described to affect the third, sixth, and rarely the fourth cranial nerves after external beam or gamma knife radiation therapy to the sellar/cavernous sinus region. The characteristic clinical finding is an intermittent, incomitant misalignment with associated diplopia that can last seconds to minutes, often evoked by eccentric gaze. Onset ranges between 2 months and 18 years after radiation (2). Only 2 cases of facial neuromyotonia, both after external beam therapy, have been documented in the literature. Department of Ophthalmology, University of Washington, Seattle, Washington. Supported by an unrestricted grant from Research to Prevent Blindness. The funding organization had no role in the design or conduct of this research. The authors report no conflicts of interest. Address correspondence to Courtney E. Francis, MD, Department of Ophthalmology, University of Washington, Box 359608, 325 Ninth Avenue, Seattle, WA 98104; E-mail: [e-mail] Rivera et al: J Neuro-Ophthalmol 2021; 41: e73-e74 FIG. 1. Axial T1 postcontrast MRI. A left cerebellopontine angle tumor measuring 7 · 11 · 7 mm. e73 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence FIG. 2. A. During an episode of left facial neuromyotonia. B. After treatment, the episodes resolved. Marti-Fabregas et al reported a case of bilateral facial nerve neuromyotonia with associated trigeminal nerve involvement 14 months after external beam irradiation of a tonsillar tumor. The patient developed an intermittent and involuntary contraction of lower facial and masticatory muscles, with EMG demonstrating involvement of bilateral orbicularis oris muscles (3). In another report, Liu et al described a case of facial neuromyotonia involving the left mentalis muscles 11 years after irradiation of a nasopharyngeal carcinoma. Physical examination findings revealed atrophy and spontaneous contraction of the left mentalis muscles without involvement of any other facial nerve controlled muscles (4). This is an unusual case of isolated facial nerve neuromyotonia after gamma knife radiation therapy. Radiation therapy has been well documented to affect cranial nerves III, IV, and VI but even the increased accuracy of gamma knife radiation, the surrounding cranial nerves may be affected resulting in facial neuromyotonia. Repeat MRI showed stable size of our patient’s schwannoma, consistent with the proposal that gamma knife radiation was responsible for symptoms. Our report demonstrates facial nerve neuromyotonia should be considered in the differential diagnosis of a patient presenting with intermittent facial contractions after radiation therapy. In the case of our patient, this was mistaken for hemifacial spasm despite the duration of her muscle contractions during episodes, and she was initially referred e74 for possible botulinum toxin treatment. Instead, carbamazepine was prescribed as it has been shown to be effective for treating other cases of myotonia (2,3,5) and fortunately led to resolution of her symptoms. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: C. E. Francis; b. Acquisition of data: C. E. Francis, C. Z. Rivera, and A. M. Solomon; c. Analysis and interpretation of data: C. E. Francis, C. Z. Rivera, and A. M. Solomon. Category 2: a. Drafting the manuscript: C. Z. Rivera and A. M. Solomon; b. Revising it for intellectual content: A. M. Solomon and C. E. Francis. Category 3: Final approval of the completed manuscript: C. E. Francis. REFERENCES 1. Berger PS, Bataini JP. Radiation-induced cranial nerve palsy. Cancer. 1977;40:152–155. 2. Much JW, Weber ED, Newman SA. Ocular neuromyotonia after gamma knife stereotactic radiation therapy. J Neuroophthalmol. 2009;29:136–139. 3. Marti-Fabregas J, Montero J, Lopez-Villegas D, Quer M. Postirradiation neuromyotonia in bilateral facial and trigeminal nerve distribution. Neurology. 1997;48:1107–1109. 4. Liu LH, Chen CW, Chang MH. Post-irradiation myokymia and neuromyotonia in unilateral tongue and mentalis muscles: report of a case. Acta Neurol Taiwan. 2007;16:33–36. 5. Sze WC, McQuillan J, Plowman PN, MacDougall N, Blackburn P, Sabin HI, Ali N, Drake WM. Stereotactic radiosurgery XX: ocular neuromyotonia in association with gamma knife radiosurgery. Endocrinol Diabetes Metab Case Rep. 2015;2015:140106. Rivera et al: J Neuro-Ophthalmol 2021; 41: e73-e74 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.