Ocular neuromyotonia. A clinical description of six patients

Non-nystagmus hyperkinetic eye movement disorders

BACKGROUND

While nystagmus is an involuntary ocular movement relatively frequent, well described, and easily recognized by most practitioners, non-nystagmus hyperkinetic eye movement disorders (NHEMD) are less obvious and can be overlooked. NHEMD may arise from intrinsic abnormalities in ocular muscles and oculomotor nerves, brain and brainstem lesions, systemic diseases, dysimmune disorders, drugs or can even be functional in nature. Given that some treatable disorders initially manifest with NHEMD, their knowledge becomes crucial.

AIMS

This review aims to offer a practical and comprehensive guide to recognize specific types of NHEMD, to choose the appropriate diagnostic tests and treatments.

RESULTS

The review approaches individual NHEMD based on the location of anatomical lesions and the underlying pathophysiological mechanisms; therefore, it begins with those arising from abnormalities in extraocular muscles or oculomotor nerves (as for example, superior oblique myokymia and ocular neuromyotonia), then moves to NHEMD due to brainstem and brain involvement (as for example, ocular bobbing, opsoclonus, and tonic downward gaze deviation). Lastly, functional NHEMD and nonnystagmus ocular hyperkinesias associated with specific neurological disorders, such as Parkinson's disease or blepharospasm will be considered.

CONCLUSION

Overall, the review offers a comprehensive reappraisal of hyperkinetic disorders of eye motility.

Ocular Neuromyotonia: Clinical Features, Diagnosis, and Outcomes

PURPOSE

The purpose of this study was to describe the clinical features, management, outcomes, and diagnostic pitfalls in a large series of patients with ocular neuromyotonia.

DESIGN

Retrospective cohort.

METHODS

Patients diagnosed with ocular neuromyotonia from January 1, 2004, through January 1, 2023, seen at one of the 3 Mayo Clinic sites in Rochester, MN, Scottsdale, AZ, and Jacksonville, FL, comprised the study population. We ascertained patients with ocular neuromyotonia through a search using the medical records database. Only patients with an observed episode of ocular neuromyotonia were included and the medical records were reviewed. The main outcome measures were clinical features and outcomes of patients with ocular neuromyotonia.

RESULTS

Forty-two patients who were diagnosed with ocular neuromyotonia were included. The median age was 58 years (range, 16-80 years). A history of cranial radiation therapy was present in 39 patients (93%). The sixth cranial nerve was involved in 31 patients (74%). Bilateral disease was found in 2 patients (5%). The median time from onset of diplopia to diagnosis was 8 months (range, 1 month-25 years), with a high rate of initial misdiagnosis in 52%. Twenty of 42 patients (48%) were treated with oral medication, of whom 95% had significant improvement or resolution of symptoms.

CONCLUSION

Prior cranial irradiation is the most common cause for ocular neuromyotonia, affecting the sixth cranial nerve most often. Although delayed and initial misdiagnosis is common, most patients show improved symptoms on medical treatment.

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.

Ocular Neuromyotonia in Children and Adolescents Following Radiation Treatment of Pediatric Brain Tumors

PURPOSE

To report five cases of ocular neuromyotonia in children and adolescents following radiation therapy for a variety of pediatric brain tumors. Notably, three cases occurred in children younger than 11 years.

METHODS

Case series of five patients with ocular neuromyotonia following proton beam therapy or conventional radiation.

RESULTS

Five cases of ocular neuromyotonia were identified following radiation treatment of various pediatric brain tumors. Onset ranged from 5 to 142 months after radiation treatment. The abducens nerve/lateral rectus muscle was affected in three patients, and the trochlear nerve/superior oblique muscle was affected in two patients. Ages at symptom presentation were 4 years (intermittent head tilt), 9 years (intermittent blurry vision and head tilt), 10 years (intermittent blurry vision progressing to intermittent diplopia), 15 years (intermittent diplopia), and 17 years (intermittent diplopia). One patient improved with gabapentin. Two patients experienced spontaneous resolution. One patient died due to meta-static disease, and one patient has planned follow-up.

CONCLUSIONS

Ocular neuromyotonia occurs most commonly following radiation to the brain and skull base. Clinicians need to be aware that ocular neuromyotonia presents differently in children (who may not report diplopia) than in adults or adolescents (who typically report diplopia). Two children in this series never reported diplopia, only intermittent head tilt and blurry vision. Ocular neuromyotonia requires a high index of suspicion to diagnose, especially in children. Membrane stabilizers can be used effectively, but observation may be a valid option in children because spontaneous resolution was seen. [J Pediatr Ophthalmol Strabismus. 2022;59(5):338-343.].

Shared Features of the Heimann-Bielshowsky Phenomenon and Ocular Neuromyotonia

We describe a case of unusual ocular movement with features of both the Heimann-Bielshowsky Phenomenon and Ocular Neuromyotonia that might suggest that they share some common pathophysiology or be on a spectrum of abnormal firing of ocular motor cranial nerves. We are the first to propose such a relationship.

Bilateral oculomotor ocular neuromyotonia: a case report

BACKGROUND

Ocular neuromyotonia (ONM) is characterized by episodic diplopia, which is usually triggered by prolonged eccentric gaze of the affected extraocular muscles. The spell is characterized by involuntary, occasionally painful, sustained contraction of one or more extraocular muscles innervated by the oculomotor, trochlear, or abducens nerve. ONM usually occurs as a late consequence of radiotherapy around the parasellar area, although idiopathic cases have been reported. Most cases are unilateral; however, bilateral ONM has occasionally been described.

CASE PRESENTATION

A 60-year-old woman presented with a 4-month history of episodic, painful, horizontal binocular diplopia. She underwent external beam radiotherapy to the skull base for treatment of nasopharyngeal carcinoma. The tumor was well controlled. General neurological examination findings were unremarkable. Neuro-ophthalmic examination revealed normal visual acuity, visual fields, pupils, and fundi. Ocular alignment showed orthotropia with normal ocular motility. Myasthenic eyelid signs were absent. However, she developed episodes of involuntary sustained contraction of the medial rectus muscle following prolonged eccentric gaze toward the affected medial rectus muscle, which resulted in esotropia upon returning to the primary position. The esotropic episodes spontaneously resolved after approximately 2 min. These spells affected both medial rectus muscles. Both pupils remained normal throughout the examination. Magnetic resonance imaging revealed neither brain parenchyma/brain stem lesions nor tumor recurrence. Her symptoms were successfully treated with carbamazepine.

CONCLUSIONS

Episodic esotropia in the adducting eye following prolonged horizontal eccentric gaze is a significant characteristic of ONM affecting the bilateral medial rectus muscles (i.e., bilateral oculomotor ONM). In spite of its extreme rarity, ONM should be considered as a differential diagnosis of episodic diplopia, especially in patients with a history of radiotherapy around the parasellar area. Careful examination with prolonged eccentric gaze should be performed to achieve a correct diagnosis and avoid an extensive unnecessary workup.

A Puzzling Ocular Motility Disorder: Apparent Up-Gaze Fatigability in a Patient With Oculomotor Nerve Compression

We report the case of a woman who developed right third nerve dysfunction with synkinesis and ocular neuromyotonia secondary to a compressive arterial aneurysm. Surprisingly, our examination showed a downward drift of the right eye in sustained up-gaze resulting in transient hypotropia, suggesting either fatigability of the superior rectus or contraction of the inferior rectus. We believe this ocular motility pattern is secondary to a co-contraction of the inferior rectus in up-gaze caused by synkinesis (explaining the downward drift), followed by failure of the inferior rectus to relax upon return to primary position caused by ocular neuromyotonia (explaining the hypotropia).

Extensive Postradiation Ocular and Diffuse Cranial Neuromyotonia Mimicking Myasthenia Gravis

BACKGROUND

Ocular neuromyotonia is a rare, but well-recognized, complication of cranial irradiation.

CASE REPORT

Using figures and videos, we report a 52-year-old man with extensive ocular, brainstem, and lower cranial nerve neuromyotonia postradiation therapy for a fourth ventricle glioma who, in the context of an apparently positive edrophonium test, was initially misdiagnosed with myasthenia gravis.

CONCLUSIONS

This is the first case of postirradiation neuromyotonia to be reported with such extensive cranial nerve and brainstem involvement.

Therapy of Vestibular Paroxysmia, Superior Oblique Myokymia, and Ocular Neuromyotonia

OPINION STATEMENT

Neurovascular compression syndromes are characterized by recurrent attacks of neurological symptoms and clinical signs depending on the cranial nerve affected. It is assumed that pulsatile compression of the nerve is caused mainly by an artery. The result is segmental demyelination of the transition zone or the central part of the cranial nerve, which is covered by oligodendrocytes, and subsequent ephaptic axonal transmission. Compression of the vestibular nerve can cause attacks of spinning or non-spinning vertigo: vestibular paroxysmia. Compression of the trochlear nerve is characterized by attacks of monocular oscillopsia: superior oblique myokymia. Damage to ocular motor nerves due to local radiation or rarely neurovascular compression can also lead to oscillopsia and double vision precipitated by sustained excentric gaze: ocular neuromyotonia. It is important to note that controlled trials have so far not been performed for any of these three syndromes, mainly because of their low prevalence. Therefore, treatment recommendations are based on single cases or small case series and thus have the lowest level of evidence. The sodium channel blockers carbamazepine (50 to 200 mg tid) or oxcarbazepine (100 to 300 mg tid) are evidently effective in most of the patients who have these three syndromes. However, one should always keep in mind the contraindications, side effects, and interactions with other drugs of carbamazepine ( http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682237.html ) All patients require regular laboratory examinations. Alternatives are other sodium channel blockers such as phenytoin (100 to 300 mg tid), gabapentin (100 to 600 mg tid), or valproic acid (100 to 300 mg tid). Furthermore, there are also few reports on the effects of beta blockers, which may be explained by their reduction of the amplitude of blood pressure. Patients who do not respond to pharmacotherapy require further diagnostics to determine the possibility of other etiologies. Some of these patients benefit from surgical decompression of the affected nerve.

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

BACKGROUND

Ocular neuromyotonia (ONM) 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 ONM.

METHODS

We describe 3 patients with sixth nerve paresis and ONM 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. Preoperative and postoperative data are presented and analyzed.

RESULTS

Two patients were noted to have ONM after their first strabismus surgery for a sixth nerve palsy. Patients 1 and 2 had 3 surgeries, whereas Patient 3 had 1 operation. Extraocular muscles operated on included the medial rectus and lateral rectus. Preoperative primary gaze baseline esotropia ranged from 35 to 75 prism diopters (Δ). All patients achieved improvement in ocular alignment and motility. Postoperative 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 ONM of a paretic rectus muscle can achieve binocular fusion with strabismus surgery. ONM may manifest postoperatively in patients with a sixth nerve palsy and a contractured medial rectus who, preoperatively, were not noted to have ONM.

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.

Ocular Neuromyotonia Associated with Chronic Inflammatory Demyelinating Polyneuropathy

Ocular neuromyotonia (ONM) is a neuro-ophthalmic disorder characterized by episodic diplopia caused by contraction of one or more ocular muscles due to spontaneous excitation of the respective ocular motor nerve. We report a patient whose ocular neuromyotonia arose in the setting of a subacute demyelinating polyneuropathy consistent with chronic inflammatory demyelinating polyneuropathy (CIDP) and subsequently resolved following the initiation of intravenous immunoglobulin (IVIg) for her neuropathy. Our patient provides additional evidence towards the role of demyelination and ephaptic neurotransmission in ocular neuromyotonia and also represents the first reported case of ocular neuromyotonia associated with a systemic neurological condition.

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

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.

[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.

Ocular neuromyotonia treated by microvascular decompression: usefulness of preoperative 3D imaging

Ocular neuromyotonia is a rare ocular motility disorder characterized by involuntary contraction of extraocular muscles resulting in paroxysmal diplopia. Although ocular neuromyotonia is reported as a rare complication after radiation therapy, there are a few cases of ocular neuromyotonia in the absence of irradiation. In the reported cases the possibility of vascular compression has been suggested on radiological imaging. The authors report a case of ocular neuromyotonia treated by microvascular decompression of the third cranial nerve, supporting the hypothesis that neurovascular compression may play a role in its pathogenesis. The usefulness of preoperative 3D imaging for microvascular decompression is also discussed.

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.

Visual outcomes after treatment of pituitary adenomas

Pituitary adenomas frequently manifest with neuro-ophthalmic symptoms and signs. The location of the pituitary gland makes involvement of both the visual pathways and the ocular motor cranial nerves likely when there is adenomatous expansion. A sudden expression of visual loss or diplopia commonly accompanies pituitary apoplexy. Several preoperative neuro-ophthalmic indicators help predict posttreatment outcomes and help determine the best intervention. Treatments themselves may also cause neuro-ophthalmic complications. The current literature and avenues of future research are reviewed.

Infranuclear ocular motor disorders

This chapter covers the very large number of possible disorders that can affect the three ocular motor nerves, the neuromuscular junction, or the extraocular muscles. Conditions affecting the nerves are discussed under two major headings: those in which the site of damage can be anatomically localized (e.g., fascicular lesions and lesions occurring in the subarachnoid space, the cavernous sinus, the superior orbital fissure, or the orbit) and those in which the site of the lesion is either nonspecific or variable (e.g., vascular lesions, tumors, "ophthalmoplegic migraine," and congenital disorders). Specific comments on the diagnosis and management of disorders of each of the three nerves follow. Ocular motor synkineses (including Duane's retraction syndrome and aberrant regeneration) and disorders resulting in paroxysms of excess activity (e.g., neuromyotonia) are then covered, followed by myasthenia gravis and other disorders that affect the neuromuscular junction. A final section discusses disorders of the extraocular muscles themselves, including thyroid disease, orbital myositis, mitochondrial disease, and the muscular dystrophies.

Abducens Nerve Ocular Neuromyotonia Following Non-sellar or Parasellar Tumors

Ocular neuromyotonia is an uncommon disorder resulting from episodic involuntary discharge of ocular motor nerves producing sustained contraction of their respective ocular muscles. Ocular neuromyotonia manifests in brief spells of diplopia occurring spontaneously or after eccentric gaze holding. In most cases, ocular neuromyotonia follows months or years after radiotherapy to the sellar and parasellar region and involves the oculomotor nerve. We report two unusual cases of abducens nerve ocular neuromyotonia that followed radiation therapy of tumors in areas other than the sellar or parasellar region.

Ocular neuromyotonia in a 15-year-old girl after radiation therapy

A 15-year-old girl, previously treated with radiation, chemotherapy, and surgery for a posterior fossa medulloblastoma and parasellar metastasis at age 8, presented with a 10-month history of episodic horizontal diplopia. She was diagnosed with ocular neuromyotonia and successfully treated with oral carbamazepine. Given the strong association between peripheral neuromyotonia and the presence of autoimmune antivoltage-gated potassium channels, the patient's blood was tested and found negative for these autoantibodies. This is the first time this has been verified in a person with ocular neuromyotonia.

[Ocular neuromyotonia after radiation therapy]

Ocular neuromyotonia is a rare disease that is diagnosed mainly in patients treated with radiation. All such patients described in the literature presented with temporary diplopic images as a common symptom. In our case, the patient described an abducens paresis of the right eye combined with a sporadic exotropia half a year after radiation treatment of an epipharynx carcinoma. An adduction deficit on the right side could be triggered by holding the gaze to the right over a longer period of time, leading to exotropia in the primary position and gaze to the left. Symptoms were reduced with carbamazepine.

Abducens neuromyotonia due to internal carotid artery aneurysm

Ocular neuromyotonia refers to paroxysmal involuntary contraction of one or more ocular muscles resulting in paroxysmal diplopia and strabismus. A 73-year-old woman reported spells of horizontal diplopia that usually developed after leftward gaze and mostly lasted less than one minute. Between the episodes, the extraocular movements were normal without aberrant regeneration. The diplopic paroxysms could be triggered by leftward gaze for several seconds. During the episode, the left eye was exotropic with mild adduction limitation. Brain imaging revealed an aneurysm in the left internal carotid artery. The episodes resolved with carbamazepine. Aneurysm of the internal carotid artery is a rare cause of abducens neuromyotonia. A compressive lesion may give rise to ocular neuromyotonia even in the absence of prior irradiation.

Ocular neuromyotonia with spastic lid closure

Ocular neuromyotonia is characterized by tonic spasms of extraocular muscles evoked by eccentric gaze that induces transient strabismus and diplopia. We report the case of a 70-year-old woman who initially presented with unilateral deficits in fifth and sixth cranial nerve functions attributed to a fifth cranial nerve schwannoma. After radiation treatment, she developed neuromyotonia and synkinesis of the ipsilateral third cranial nerve. During the attacks of neuromyotonia, the left eyelids were often spastically closed, a phenomenon not previously reported. The ocular neuromyotonia regressed spontaneously within 3 years, but components of the synkinesis persisted. Ephaptic transmission in a damaged third cranial nerve may be responsible for the neuromyotonia and synkinesis. Synkinesis is a more enduring manifestation.

Primary Aberrant Regeneration and Neuromyotonia of the Third Cranial Nerve

A 52-year-old woman presented with episodic diplopia with a duration of 6 months. Between the episodes, infraduction of the right eye was mildly impaired with retraction of the right upper lid on downgaze. On resuming the primary position after prolonged left gaze, she developed a right esotropia and reduced abduction, supraduction, and infraduction of the right eye. There was no history of cranial radiation or previous diagnosis of a brain lesion. Brain imaging results were negative. The interictal infraduction deficit and lid retraction were interpreted as signs of a mild right third cranial nerve palsy with primary aberrant regeneration. The episodic esotropia and ductional deficits were considered to be signs of neuromyotonia. This combination of findings, rarely described before, suggests a link between primary aberrant regeneration and neuromyotonia. Abnormal and excessive conduction triggered by stimulation of a partially damaged nerve probably underlies ocular neuromyotonia.

Neuromyotonie post-radique du masséter

INTRODUCTION

Neuromyotonia is a late and rare complication of radiation therapy, consisting of involuntary sustained muscle contractions with a delay in relaxation.

OBSERVATION

We report the case of a 68-year-old man who developed neuromyotonia of the masseter muscle 6 years after irradiation for tonsil carcinoma.

CONCLUSION

This observation underlines the importance of a correct diagnosis that can lead to an efficient treatment by carbamazepine.

Adult-onset acquired oculomotor nerve paresis with cyclic spasms: relationship to ocular neuromyotonia

PURPOSE

To describe the characteristics and significance of acquired oculomotor nerve paresis with cyclic spasm.

METHOD

Retrospective case series of two patients with a history of previous skull base irradiation for intracranial tumor who developed double vision and were found to have oculomotor nerve paresis with cyclic spasm. Both patients underwent a complete neuroophthalmologic assessment, including testing of eyelid position, pupillary size and reactivity, and ocular motility and alignment during both the paretic and spastic phases of the condition.

RESULTS

Both patients developed unilateral lid retraction and ipsilateral esotropia with limitation of abduction during the spastic phase of the cycle, with ipsilateral ptosis, exotropia, and variable limitation of adduction during the paretic phase. The cycles were continuous and were not induced or altered by eccentric gaze.

CONCLUSIONS

Cyclic oculomotor nerve paresis with spasms may occur years after irradiation of the skull base. This condition is different from the more common ocular motor disturbance that occurs in this setting-ocular neuromyotonia. However, in view of the similarity between these two disorders, it seems likely that they are caused by a similar peripheral mechanism.

Ocular neuromyotonia: a case report

Ocular neuromyotonia is a rare clinical entity, which is characterized by spontaneous spasm of ocular muscles resulting in paroxysmal diplopia and strabismus. Inappropriate discharges from ocular motor neurons or axons with unstable cell membranes may cause the sustained contraction of their respective ocular muscles. In most cases, ocular neuromyotonia resulted from radiation therapy to the parasellar and sellar regions or compressive lesions on ocular motor nerves. Among 30 patients reported in the literatür only six patients were accepted as idiopathic. Here, we reported a patient with third nerve myotonia representing with spells of diplopia. No lesion was found and she was accepted as idiopathic ocular neuromyotonia.

Abduction paralysis with hypotropia: sign of weakness of a contralateral superior oblique

background The clinical diagnosis of extraocular motor paralysis that is caused by severe cranial trauma can often be complicated. The resulting clinical picture can make the identification of all the components of potentially treatable oculomotor problems difficult. methods We examined five cases of complete abducens nerve paralysis with marked downshoot in attempted abduction seen after severe cranial trauma. results With the patients looking in the field of gaze of the paralysis, a marked infraductive movement of the paralytic eye occurred while the other eye maintained fixation. Other clinical findings confirmed this to be a secondary deviation due to a paresis of the contralateral superior oblique. conclusion Patients with a paralysis of the lateral rectus following a severe cranial trauma who demonstrate a marked downshoot of the involved eye should be suspected of having a paresis of the contralateral superior oblique. This diagnosis has helped us effectively to treat this vertical incomitance by a simple weakening procedure of the contralateral inferior oblique.

Conduction block and continuous motor unit activity in chronic acquired demyelinating polyneuropathy

The term continuous motor unit activity (CMUA) may be used to refer to the involuntary, sustained activity of motor units caused by hyperactivity of peripheral motor nerves. CMUA has been reported in association with acquired neuropathies such as chronic inflammatory demyelinating polyneuropathy. The precise mechanism responsible for the excess muscle activity is not defined, but the activity is believed to originate in the peripheral nerves, perhaps at sites of focal demyelination. We describe a case of an acquired, demyelinating neuropathy associated with distal motor conduction block in which CMUA was observed in muscles innervated by blocked axons. Despite the prolonged disease duration of nearly 40 years, marked clinical and electrophysiological improvement as well as resolution of the CMUA were observed following immunosuppressive therapy. A relationship between the chronic motor conduction block and the excess muscle activity is postulated.

Ocular neuromyotonia in a patient with cavernous sinus thrombosis secondary to mucormycosis

PURPOSE

To report a case of ocular neuromyotonia occurring after cavernous sinus thrombosis secondary to mucormycosis.

METHODS

Case report. We performed serial comprehensive neuro-ophthalmologic examinations.

RESULTS

Fifteen months after initial total ophthalmoplegia of the right eye and complete right upper eyelid ptosis, isolated ocular neuromyotonia, characterized by episodic upward jerking movements of the right upper eyelid, was noted.

CONCLUSION

Ocular neuromyotonia, which usually manifests in patients with a history of intracranial tumors and cranial radiation, may also be secondary to infectious cavernous sinus thrombosis.

Ocular neuromyotonia

AIMS/BACKGROUND

Ocular neuromyotonia is characterised by spontaneous spasm of extraocular muscles and has been described in only 14 patients. Three further cases, two with unique features, are described, and the underlying mechanism reviewed in the light of recent experimental evidence implicating extracellular potassium concentration in causing spontaneous firing in normal and demyelinated axons.

METHODS

Two patients had third nerve neuromyotonia, one due to compression by an internal carotid artery aneurysm, which has not been reported previously, while the other followed irradiation of a pituitary tumour, a common association in the published reports. Selective activation occurred in both, where neuromyotonic activity was triggered by prolonged voluntary activation of specific extraocular muscles with or without spread of activity to other third nerve muscles. The other patient had fourth nerve involvement, where spasms of the superior oblique muscle were induced only by alcohol, a phenomenon which has not been described.

RESULTS

The two patients with third nerve involvement responded to carbamazepine and in one, an improvement in a chronic partial third nerve paresis occurred. The other has not required treatment and remains asymptomatic by refraining from alcohol.

CONCLUSIONS

A careful examination, including the effects of prolonged voluntary muscle action is required to initiate episodes and to demonstrate selective activation. Imaging is mandatory to exclude compressive intracranial lesions, particularly where there is no history of pituitary fossa irradiation. A trial of anticonvulsants should be considered in all patients. Extracellular potassium may play a role in spontaneous firing and ephatic transmission in ocular neuromyotonia.

Paroxysmal superior rectus and levator palpebrae spasm: a unique presentation of multiple sclerosis

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Ocular neuromyotonia: clinical features, physiological mechanisms, and response to therapy

Ocular neuromyotonia (ONM) is a rare disorder characterized by episodic diplopia, occurring either spontaneously or following sustained eccentric gaze. Most patients have had prior radiation therapy to the sellar and parasellar region. ONM is thought to reflect impaired muscle relaxation due to inappropriate discharges from oculomotor, trochlear, or abducens neurons or axons with unstable cell membranes. Patients with ONM often benefit from membrane stabilizing agents such as carbamazepine. Here we describe a 71-year-old man, with no history of radiation therapy, who for 18 months had had transient episodic diplopia that occurred after down gaze. Clinical examination indicated ONM in muscles supplied by the right oculomotor nerve. Binocular scleral search coil eye movement recordings revealed a defect not only of muscle relaxation but also of maximal muscle contraction. The patient was treated with carbamazepine 200 mg per day with complete resolution of his symptoms. ONM may be more common than previously recognized, and patients with unexplained transient episodic diplopia should be specifically tested for diplopia and ocular misalignment following sustained eccentric gaze.

AAEM minimonograph #44: diseases associated with excess motor unit activity

Stiff-man syndrome is due to hyperexcitability of anterior horn cells, possibly related to interference with the synthesis or action of gamma-aminobutyric acid. Unexpected acoustic and exteroceptive stimuli produce exaggerated muscle responses. Needle electrode examination of involved muscles yields nonspecific findings and demonstrates involuntary motor unit activity. The appearance and firing pattern of motor units are normal except that agonist and antagonist muscles may contract concurrently. Continuous muscle fiber activity (Isaacs' syndrome) comprises a heterogeneous group of hereditary and acquired disorders that cause hyperexcitability of peripheral nerves. Some are associated with electrophysiologic evidence of peripheral neuropathy and some are not. Repetitive afterdischarges often follow the M-, H-, and F-waves. Needle electrode examination reveals an abnormal pattern of motor unit firing, consisting of myokymic discharges, doublets and multiplets, neuromyotonic discharges, and fasciculations. These abnormalities may occur alone or in combination.

Gaze-induced strabismus

A 20-year-old woman with a past history of a sinonasal undifferentiated carcinoma involving the skull base and cavernous sinus, previously treated with surgery and radiation therapy, presented with intermittent horizontal diplopia induced by gaze to the right side. The gaze in the direction of the action of the right VI nerve produced sustained contraction of the right lateral rectus and an exodeviation increasing on left gaze. Ocular neuromyotonia involving the right VI nerve was believed to be secondary to the patient's previous radiation therapy. The discussants review the prior literature regarding ocular neuromyotonia involving the III, IV and VI cranial nerves, its relationship to prior radiation therapy, and possible modes of therapy including the use of Carbamazepine.

Episodic exotropia from lateral rectus neuromyotonia--appearance and remission after radiation therapy for a thalamic glioma

Sixteen months after radiation therapy for a moderately anaplastic astrocytoma of the thalamus, a 7-year-old boy developed spontaneous episodic contractions in his left lateral rectus muscle. During these episodes, lasting 10 to 30 seconds and occurring 20 or more times a day, he had exotropia, limitation of adduction, and retraction of the left globe. This phenomenon peaked in duration and frequency at 14 months and gradually disappeared after 22 months. As this case confirms, radiation injury to the abducens nerve can cause ocular neuromyotonia, resulting in episodic strabismus. Our case also illustrates that this condition can disappear completely after many months.