Eyelid myokymia caused by a trigeminal schwannoma as determined by the trigeminal‐evoked blink reflex

Abstract

A 57‐year‐old man had trigeminal schwannoma in Meckel's cave with eyelid myokymia only. The evaluation of the trigeminal‐evoked blink reflex was useful for confirming eyelid myokymia and contributed to surgical decision‐making. In patients with persistent eyelid myokymia, neurophysiological and imaging evaluations may be useful for determining the underlying pathophysiology.

1. INTRODUCTION

Eyelid myokymia is a localized involuntary contraction of the orbicularis oculi muscle, a self‐limiting condition that lasts for seconds to hours, and rarely for weeks. ¹ , ² This entity, which is considered benign, originates from peripheral nerves and is triggered by extrinsic factors such as stress, excessive caffeine consumption, drugs, viral infection or physical exertion; central nervous system diseases are rarely the cause. ³ , ⁴ , ⁵ Although several cases of eyelid myokymia associated with intracranial lesions have been reported, its pathogenesis remains unclear. ⁶ , ⁷ , ⁸ , ⁹ , ¹⁰ , ¹¹ We describe the case of a patient with trigeminal schwannoma localized to the Meckel's cave, who presented with eyelid myokymia, as determined by the trigeminal‐evoked blink reflex.

2. CASE REPORT

A 57‐year‐old man was referred to our hospital because of left eyelid myokymia associated with a persistent lateral pulling sensation for 3 months. The patient had no relevant medical history. Physical examination revealed normal rhythmic contractions of the left eyelid. Eyelid myokymia was confined to the left upper and lower eyelids and it did not spread to the forehead or corners of the mouth. The patient's corneal reflexes were bilaterally normal. There was no evidence of left facial pain or dysesthesia arising from left trigeminal neuropathy or left facial palsy. No other neurological manifestations were detected in the central or peripheral nervous systems.

A head computed tomography (CT) scan showed a neoplastic lesion with partial calcification in Meckel's cave of the left trigeminal nerve (Figure 1). Magnetic resonance imaging (MRI) revealed that the mass lesion was hyperintense on T1‐weighted images (gadolinium enhancement; Figure 2), isointense on T2‐weighted images (Figure 3), and heterogeneously hypointense on susceptibility‐weighted imaging (SWI; Figure 4). Compressive lesions on T2‐weighted MRI (Figure 5) and culprit vessels on magnetic resonance angiography (Figure 6) were absent at the root exit zone of the left facial nerve. Positron emission tomography revealed little methionine accumulation in the same area, and the tumor‐to‐normal tissue ratio was 1.43, consistent with neurinomas. Cerebral angiography revealed little tumor staining and no vascular lesions.

FIGURE 1.

Preoperative axial computed tomography scan showing a mass lesion with partial calcification in the Meckel's cave of the left trigeminal nerve.

FIGURE 2.

Preoperative axial T1‐weighted magnetic resonance imaging with gadolinium revealed a hyperintense lesion localized to the left Meckel's case.

FIGURE 3.

Preoperative axial T2‐weighted magnetic resonance imaging revealed a mass lesion localized to the left Meckel's cave.

FIGURE 4.

Preoperative axial susceptibility‐weighted imaging revealed a heterogeneous hypointense lesion localized to the left Meckel's cave.

FIGURE 5.

Preoperative axial T2‐weighted imaging revealed no compressive lesions at the exit of the left facial nerve.

FIGURE 6.

Preoperative axial magnetic resonance angiography revealed no culprit vessels at the exit of the left facial nerve.

Based on these findings, we suspected trigeminal schwannoma localized to the left Meckel's cave. However, as the initial symptom was not typical of trigeminal schwannoma, we measured the patient's trigeminal‐evoked blink reflex. Compared to the healthy side, there was no latency prolongation; however, upon stimulation of the left supraorbital nerve, the R1 and R2 amplitudes on the left side were lower (R1 amplitude: right, 180 μV; left, 10 μV; left/right R1 amplitude ratio: 0.05; Figure 7A). Therefore, we determined that the symptoms were caused by the left trigeminal schwannoma and thus decided on surgical intervention.

FIGURE 7.

Blink reflex in response to supraorbital nerve stimulation. The upper pairs of traces represent reflex responses in the right (R) and left (L) orbicularis oculi muscles after stimulation of the right supraorbital nerve (R*). The lower pairs of traces represent reflex responses in the right (R) and left (L) orbicularis oculi muscles after stimulation of the left supraorbital nerve (L*). (A) Preoperative blink reflex. The ipsilaterally stimulated left R1 response (arrow) was smaller than the ipsilaterally stimulated right R1 response (arrowhead). (B) Postoperative blink reflex. The ipsilaterally stimulated left R1 response (white arrow) was equivalent to the ipsilateral stimulated right R1 response (white arrowhead).

Under general anesthesia, we performed left temporal craniotomy with zygomatic osteotomy. After implementing the intradural subtemporal approach, the dura above Meckel's cave was incised. The highly viscous and partially calcified tumor was identified and the Meckel's cave was filled. The tumor capsule adhered to several normal bundles of the trigeminal nerve, and subcapsular removal was performed. The bundles were entrapped by the tumor, and looped blood vessels were present in the space between the tumor and the trigeminal nerve. The calcified lesions in the tumor could not be removed without sacrificing the normal bundles of the trigeminal nerve. In addition, the petrous portion of the internal carotid artery passed under the calcified lesions, as confirmed by intraoperative navigation and micro‐Doppler imaging. Therefore, partial removal was performed to maintain normal function.

The postoperative course was uneventful and the patient had no neurological deficits. Immediately after the surgery, the patient's left eyelid myokymia disappeared. Four months after the surgery, the trigeminal‐evoked blink reflex showed that the R1 and R2 amplitudes on the left side had recovered without latency prolongation (R1 amplitude: right, 85 μV; left, 58 μV; left/right R1 amplitude ratio: 0.68; Figure 7B). Furthermore, there was no growth of any residual tumor (Figure 8), and the symptoms did not flare. The pathological diagnosis was that of a schwannoma.

FIGURE 8.

Postoperative axial T2‐weighted magnetic resonance image showing a residual lesion in the left Meckel's cave.

3. DISCUSSION

Eyelid myokymia as the initial symptom of trigeminal schwannoma is rare. To the best of our knowledge, there are no prior reports of eyelid myokymia in patients with trigeminal schwannoma. Although the most common initial symptom of trigeminal schwannoma is facial hypesthesia (39.3%), ¹² symptoms such as facial pain, facial paresthesia, and diminished or absent corneal reflexes, may also manifest. The present case only had eyelid myokymia on the same side as the trigeminal schwannoma before surgery; there were no symptoms following the surgery. Thus, eyelid myokymia may be a minor initial symptom of trigeminal schwannoma.

Eyelid myokymia, although thought to originate from peripheral nerves such as the facial nerve, may be triggered by extrinsic factors ³ , ⁴ , ⁵ or the synkinetic facial nerve innervation induced by swallowing. ¹³ Furthermore, central nervous system diseases can also be a causative factor. Six cases of eyelid myokymia caused by intracranial lesions have been reported: four with multiple sclerosis, one with a medial temporal lobe tumor, and one with a pontine glioma. ⁶ , ⁷ , ⁸ , ⁹ , ¹⁰ , ¹¹ Most lesions caused by central nervous system diseases are thought to be related to the trigeminofacial reflex, in which the afferent and efferent pathways correspond to the trigeminal and facial nerves, respectively. Lesions in the nucleus and/or the supranuclear portion of the facial nerve are thought to underlie the pathophysiology of eyelid myokymia arising from a central nervous system disease. ⁸ For instance, in the case of temporal tumors, the tumor extending into the cerebral peduncle results in the suppression of the inhibitory pathway at the supranuclear level. ⁷ The present case had no lesions in the nucleus and/or the supranuclear portion of the facial nerve, and the lesion was located in the afferent pathway. Although eyelid myokymia is transient and considered benign, central nervous system disease should be suspected if the symptoms persist.

In the present case, head imaging as well as preoperative neurophysiological evaluation contributed to the determination of the causal relationship between trigeminal nerve lesions and eyelid myokymia. The relationship between the anatomical causative lesion and blink reflex was reported in detail by Aramideh et al. ¹⁴ They reported that when the trigeminal nerve trunk was affected, the R1 and R2 amplitudes decreased, and the latency prolonged upon stimulation of the affected side. However, the findings of the present case differed: the preoperative trigeminal‐evoked blink reflex showed lower R1 and R2 amplitudes and no prolongation of latency against the affected stimulus, although surgery resolved these issues.

There are three plausible explanations for our results:(1) R1 is more likely to show an acute change than R2, (2) phase cancellation of the sensory nerve action potential might have occurred, and (3) small amounts of fibers may be relatively insensitive to damage. Our results shed light on the neuropathophysiology of eyelid myokymia induced by central nervous system diseases.

Regarding the first possible mechanism, acute R1 abnormalities may be more detectable than R2 abnormalities in relation to the blink reflex. R1 was only evoked on the stimulus side in the principal trigeminal sensory nucleus and facial nucleus of the pons. As a monosynaptic circuit, R1 has short latency, making it a useful and reproducible marker for lesion diagnosis. ¹⁵ In contrast, the R2 interneuron pathway involves several synapses in the medullary tract nucleus of the trigeminal nerve and ascends from the lateral reticular formation to the ipsilateral and contralateral facial nerve nuclei. R2 may be less reproducible because of its multisynaptic circuitry and dependence on the central nervous system. ¹⁵ Ohki and Takeuchi reported that R1 and R2 reflect the functions of different sensory nerve fibers. ¹⁶ R1 reflects the function of Aβ fibers, while R2 reflects the function of both Aβ and Aδ fibers. The trigeminal nerve comprises a mixture of Aβ, Aδ, and C fibers; the thickest being Aβ fibers, followed by Aδ and C fibers. Thicker nerve fibers are more susceptible to compression and inflammation. ¹⁷ Therefore, when extrinsic physical factors affect the trigeminal nerve, the R1 findings are more likely to reflect acute changes in the blink reflex.

The second possible mechanism underlying the reduction in R1 amplitude is the phase cancellation of the SNAP. Although latency changes are generally the most reliable markers of partial nerve damage, sensory nerves may exhibit changes in amplitude only. In axonal and demyelinating pathologies, the SNAP amplitude is reduced for different reasons. Demyelinating injuries also decrease the SNAP amplitude, but they prolong its latency. ¹⁸ However, the prolonged latency is still much shorter than compound muscle action potentials and is, therefore, more susceptible to phase cancellation. ¹⁹ , ²⁰ Temporal and spatial summation at each synapse makes the trigeminal reflex more robust and its latency is essentially unaffected. ²¹ , ²² , ²³

The third possible mechanism is low sensitivity to damage caused by small amounts of trigeminal fibers. In the trigeminofacial reflex, when the efferent tract (i.e., the facial nerve) is injured, the latency gets prolonged; however, this may not be the case when the afferent tract (trigeminal nerve) is injured. In a report of trigeminal neuralgia, in which trigeminal nerve function was evaluated in terms of laser‐evoked potentials, 8 of 11 patients showed a decrease in amplitude without any prolongation of latency, and the amplitude improved after surgical treatment. ²⁴ Although Aβ fibers are involved in trigeminal nerve dysfunction (TND), ²⁵ the trigeminofacial reflex usually remains normal. ²¹ This is probably attributable to the low sensitivity to damage of small amounts of fibers, as mentioned above. ²⁴ If the afferent pathway of the trigeminofacial reflex is impaired, R1 amplitude may be reduced without prolongation of latency.

Multiple factors should be carefully considered to thoroughly evaluate the electrophysiological blink reflex. In the present case, the R2 amplitude was lower on the left side than on the right side following stimulation on the right (i.e., healthy) side. The condition of the facial nerve, the patient's body position, and the stimulating electrode in the orbicularis oculi muscle may have contributed to this finding. Further studies are needed to control for these variables.

The trigeminal‐evoked blink reflex is useful for the identification of the causative lesion, and can aid surgical and postoperative decision‐making. As mentioned above, eyelid myokymia has not been previously reported as an initial symptom of trigeminal schwannoma. In the present case, although the imaging findings confirmed a lesion in the left Gasserian ganglion, preoperatively determining whether this was the causative lesion was difficult, as the patient exhibited no other neurological deficits. However, the positive findings regarding the blink reflex directed us toward the option of surgery. Postoperatively, the patient's symptoms disappeared and thereon, the blink reflex improved. Thus, the blink reflex evaluation may facilitate the decision‐making process regarding surgical interventions.

Physical compression of the tumor and vessels in this case may have resulted in hyperexcitability changes in the trigeminal nerve. Intraoperative findings revealed the presence of a small artery between the Gasserian ganglion and the calcified tumor. The mass effect of the tumor, as well as the pulsative stimulus from the intervening vessels, may have stimulated the trigeminal nerve, resulting in the blink reflex and, in turn, eyelid myokymia. Immediately after surgery, the patient's symptoms resolved, just as the symptoms of neurovascular compression syndrome resolved following surgery. ¹⁶ , ¹⁷ Additional cases with eyelid myokymia may help establish the pathogenesis of eyelid myokymia as a neurovascular compression syndrome.

Our patient did not suffer from any form of TND, such as facial pain, facial numbness, paresthesia, or hypoesthesia. The trigeminal nerve is composed of Aβ, Aδ, and C fibers that respond to touch, sharp pain, and dull pain, respectively. Selective damage to these nerve fibers leads to different sensory disturbances. In the present case, only vulnerable Aβ fibers might have been affected; a lack of damage to the Aδ and C fibers might explain the absence of pain. In a study of 58 patients whose trigeminal nerves were affected by a surgical procedure, 32 (55%) reported no neuropathic pain, although sensory deficits occurred in all cases. ²⁶

Although our patient had no TND, the tactile sensation might have been abnormal. As R1 abnormalities are more obvious in relation to the blink reflex, it can be intuited that the Aβ fibers (sensitive to touch) were affected. The patient's failure to complain may be attributable to involuntary muscle constructions occurring because of eyelid myokymia prior to surgery.

In conclusion, we report a case of trigeminal schwannoma with eyelid myokymia only, as an uncommon initial presentation. Evaluation of the trigeminal evoking blink reflex was useful for confirming eyelid myokymia and contributed to surgical decision‐making. In patients with persistent eyelid myokymia, clinical neurophysiological and imaging evaluations may be useful for determining the underlying pathophysiology.

AUTHOR CONTRIBUTIONS

Eiji Ito: Conceptualization; formal analysis; investigation; methodology; supervision; writing – original draft; writing – review and editing. Ryotaro Sugita: Conceptualization; formal analysis; methodology; supervision; writing – original draft; writing – review and editing. Ryuta Saito: Conceptualization; project administration; writing – original draft; writing – review and editing.

ACKNOWLEDGEMENTS

None.

FUNDING INFORMATION

This research received no specific grants from any funding agency in the public, commercial, or not‐for‐profit sectors.

CONFLICT OF INTEREST STATEMENT

All the authors declare no competing interests.

ETHICAL APPROVAL

This study was performed in accordance with the ethical standards of the Japan Neurosurgical Society.

CONSENT

Written informed consent was obtained from the patient for publication of this case report and accompanying dates and images.

Ito E, Sugita R, Saito R. Eyelid myokymia caused by a trigeminal schwannoma as determined by the trigeminal‐evoked blink reflex. Clin Case Rep. 2023;11:e7086. doi: 10.1002/ccr3.7086