Abducens Neuromyotonia as the Presenting Sign of an Intracranial Tumor

Ocular neuromyotonia: a review of diagnosis and treatment

PURPOSE OF REVIEW

The current review will cover the clinical presentation, causes, epidemiology, differential diagnoses, workup, and treatment of ocular neuromyotonia (ONM) in detail.

RECENT FINDINGS

While ONM largely remains a unilateral eye movement disease affecting adults with a history of sellar radiation, recent case reports highlight an expansion of this presentation to include bilateral, pediatric, and congenital cases.

SUMMARY

ONM is a rare but recognizable ocular motility disorder involving sustained contraction of the extraocular muscle, commonly resulting in intermittent diplopia. Diagnosis of ONM relies upon a thorough history and clinical exam, with particular attention to history of radiotherapy and eccentric gaze testing. Treatment with carbamazepine remains first-line therapy, although other membrane stabilizing agents and surgical interventions can be effective.

Surgery option in the management of delayed diplopia after radiation therapy for nasopharyngeal carcinoma

PURPOSE

Radiation therapy is a standard treatment for nasopharyngeal carcinoma. Diplopia due to radiation damage to the sixth nerve significantly erodes the patient's quality of life. This study investigated the effectiveness of extraocular surgery in the treatment of delayed diplopia caused by radiation therapy.

METHODS

A retrospective case series of 16 patients (7 men and 9 women) with delayed diplopia after radiation therapy for nasopharyngeal carcinoma was enrolled in the study. Unilateral lateral rectus resection was performed under topical anesthesia. Follow-up time was more than 12 months. Outcome measures were prism diopter and self-reported symptoms.

RESULTS

All patients diagnosed with sixth nerve palsy reported elimination of symptoms on postoperative day 1 without complications. One patient required a second procedure due to recurrence of symptoms. At 12-month follow-up, no patient reported recurrence of symptoms. The absolute horizontal deviation significantly decreased from a preoperative value of 16 prism diopter to a value of 1.5 prism diopter postoperatively (p < 0.001).

CONCLUSION

These results suggest that unilateral lateral rectus resection under topical anesthesia is an effective treatment for delayed diplopia after radiation therapy for nasopharyngeal carcinoma. A large randomized prospective study to confirm these findings is warranted.

Abducens ocular neuromyotonia as a delayed complication of oropharyngeal carcinoma treated with radiation

BACKGROUND

Ocular neuromyotonia (ONM) is a disorder characterized by periodic involuntary extraocular muscle contraction that occurs almost exclusively in the setting of prior radiation to the sella or skull base. We present the first case of abducens neuromyotonia associated with oropharyngeal carcinoma.

METHODS AND RESULTS

We report a case of a 63-year-old patient with abducens ONM occurring 16 years after radiation treatment for oropharyngeal squamous cell carcinoma. A literature review was performed using Medline and PubMed databases to search for all documented cases of abducens neuromyotonia. Our review found 20 cases of abducens neuromyotonia but none after radiotherapy (RT) to the oropharynx.

CONCLUSION

Abducens ONM can occur because of disease at anatomic locations remote from the course of the sixth cranial nerve, most likely because of the irradiated area exceeding the intended field. Our case also supports the fact that RT can significantly precede symptom onset. © 2016 Wiley Periodicals, Inc. Head Neck 38: E2428-E2431, 2016.

A novel association of ocular neuromyotonia with brainstem demyelination: two case reports

Ocular neuromyotonia (ONM) is a rare disorder of ocular mal-alignment in which painless, transient spontaneous or gaze-induced abnormal deviation of the eye manifests as episodic diplopia. With only a few cases reported in the literature, ONM mostly follows months to years after cranial irradiation for sellar or suprasellar lesions. Here we present two patients with this rare ocular condition, secondary to brainstem demyelination, the association of which is hitherto unreported in the literature. Both patients were 15-year-old girls who presented to us with episodic forced-eye deviation with diplopia. Examination during these attacks revealed ONM involving the superior rectus and medial rectus in the first and second patient, respectively. There was clinical evidence of intrinsic brainstem involvement with downbeat nystagmus and skew deviation in one patient without any other cerebellar or long tract signs. MRI showed evidence of demyelination involving the brainstem in both, with CSF showing positive immunological markers and with positive aquaporin-4 antibody in one patient. Both patients responded remarkably to immunomodulatory therapy and are asymptomatic at follow-up. That ONM can occur with brainstem demyelination has not been reported in the literature. This association may help in explaining the pathophysiology of ONM as secondary to segmental demyelination.

[A case of Tolosa-Hunt syndrome presenting ocular neuromyotonia]

A 27-year-old woman noticed diplopia when gazing left and paresthesia of the left face and headache of the left side for 8 months. Abduction and supraduction of the left eye were moderately restricted. Hypoesthesia of the face innervated by the ophthalmic branch of the left trigeminal nerve was detected. Visual disturbance due to optic neuropathy developed 5 months later. MRI with gadolinium revealed a mass lesion extending from the left cavernous sinus to the orbital apex. Ocular neuromyotonia and corresponding diplopia were induced by sustained right gaze. Such episodes occurred almost every day on awaking in the morning. Prednisolone (60 mg/day) was given and the headache and visual disturbance ameliorated in two days. The diplopia disappeared in 4 days. The patient remains free from these symptoms after 6 months. This is the first report of ocular neuromyotonia associated with Tolosa-Hunt syndrome.

Novel case of ocular neuromyotonia associated with thyroid-related orbitopathy and literature review

PURPOSE

To present a novel case of pupillary involvement in ocular neuromyotonia (ONM), a rare ocular syndrome that causes intermittent diplopia because of an abnormal delay in extraocular muscle relaxation and to conduct a literature review.

METHODS

A case report is presented to demonstrate clinical characteristics and treatment of ONM. In addition, a literature review is conducted by searching Medline and Embase databases. Data are collected from all known published cases listed in these databases to collate patient demographic data, presumed etiology or associated pathologies, and treatment strategies.

RESULTS

The presented case demonstrates successful carbamazepine treatment of thyroid-related orbitopathy-associated ONM involving cranial nerve III. A review of the literature elicits 66 published cases of ONM, three of which were deemed to be associated with thyroid-related orbitopathy. The most common cause of reported ONM is suprasellar pathology, comprising approximately 60% of documented cases. Most published ONM cases (n = 41) were treated with carbamazepine, demonstrating a success rate of 87.8%. Of the published cases, cranial nerve III was involved 56% of the time, cranial nerve VI was affected in 39% of cases, and only 9% of ONM cases involved cranial nerve IV.

CONCLUSIONS

Ocular neuromyotonia is a rare cause of intermittent diplopia. Unlike most neurologic etiologies of diplopia, this syndrome can often be treated effectively with carbamazepine by stabilizing the neural cell membrane. To the authors' knowledge, this is the first presentation of ONM associated with thyroid-related orbitopathy, demonstrating bilateral but asymmetric miosis during episodes of muscle spasm.