Hemifacial spasm (HFS) is a clinically common neurological disorder of the brain, the treatment of which includes medications, botulinum toxin injections, and surgery. Although microvascular decompression is the current promising method to completely cure hemifacial spasm, postoperative ineffectiveness, recurrence, and complications such as facial palsy and hearing impairment are still a problem for physicians and patients. Since 2012, Shanghai Jiao Tong University Cranial Nerve Disease Diagnosis and Treatment Center and the Functional Neurosurgery Group of the Neurosurgery Branch of the Chinese Medical Association have convened more than 80 neurosurgeons for several times to compile a Chinese expert consensus on the treatment of facial myospasm, taking into account the research progress at home and abroad and the actual situation in China, in order to standardize and guide the clinical practice of facial myospasm treatment and improve the overall level of treatment of facial myospasm in China.
I. Overview
Facial muscle spasm refers to recurrent paroxysmal, involuntary twitching of one or both facial muscles (orbicularis oculi, expression muscles, orbicularis oris), which is aggravated by emotion or tension, and in severe cases, there may be difficulty in opening the eyes, distorted corners of the mouth and twitching-like murmurs in the ears. Typical facial spasm is a spasm that starts from the eyelids and gradually progresses downward to involve the lower facial muscles such as the cheek expression muscles, while atypical facial spasm is a spasm that starts from the lower facial muscles and gradually progresses upward to eventually involve the eyelids and frontal muscles. Atypical facial spasms are less common in clinical practice, and the vast majority are typical facial spasms. Facial myospasm is more common in middle-aged and elderly people, with slightly more women than men, but there is a trend toward younger age of onset. Although most facial myospasms are located on one side, bilateral facial myospasms are not uncommon.
Second, diagnosis and differential diagnosis
1.Diagnosis of facial myospasm
The diagnosis of facial myospasm mainly depends on the characteristic clinical manifestations. For patients lacking characteristic clinical manifestations, auxiliary examinations are needed to clarify, including electrophysiological examination, imaging examination, and carbamazepine treatment test. Electrophysiological examinations include electromyography (EMG) and abnormal muscle response (AMR) or lateral spread response (LSR) tests. In patients with facial spasm, EMG can record a high frequency of spontaneous potentials (up to 150 per second), and AMR is an abnormal muscle response specific to facial spasm, and a positive AMR supports the diagnosis of facial spasm. Imaging studies include CT and MRI to identify intracranial lesions that may be causing the facial spasm, and three-dimensional time-of-flight magnetic resonance angiography (3D-TOF-MRA) to help understand the vascular distribution around the facial nerve. Patients with facial myasthenia are generally effective with carbamazepine treatment at the beginning of the disease (a small number of patients may appear ineffective), therefore, carbamazepine treatment trials are helpful for diagnosis.
2, Differential diagnosis of facial myospasm
Facial myospasm needs to be differentiated from bilateral blepharospasm, Major’s syndrome, bite spasm, post-facial paralysis and other facial dystonia disorders.
(1) Bilateral blepharospasm: This is characterized by recurrent episodes of involuntary eye closure of both eyelids, often at the same time, and the patient often shows difficulty in opening the eyes and reduced tears.
(2) Meijer syndrome: Patients often start with recurrent episodes of involuntary eye closure of the eyelids bilaterally, but with the prolongation of the disease, involuntary twitching of the muscles below the eye fissure will gradually appear, manifesting as involuntary abnormal movements of the face bilaterally, and with the aggravation of the disease, the scope of muscle spasm will gradually expand downward, even involving the muscles of the neck, limbs and trunk.
③ Bite muscle spasm: It is a spasm of unilateral or bilateral masticatory muscles. Patients may have different degrees of upper and lower jaw occlusion disorder, teeth grinding and mouth opening difficulties, and trigeminal nerve motor branch lesion is one of the possible causes.
(4) Posterior facial palsy: It is manifested by restricted movement of the ipsilateral facial expression muscles, involuntary twitching of the ipsilateral corners of the mouth as well as concomitant movement of the corners of the mouth and eyelids, which can be identified based on the exact history of facial palsy.
Preoperative evaluation
1.Electrophysiological evaluation
Preoperative electrophysiological evaluation is helpful for differential diagnosis of facial spasm and objective understanding of the functional level of facial nerve and vestibular nerve, and should be actively carried out in hospitals with conditions. The electrophysiological evaluation mainly includes AMR (LSR), EMG and brainstem acousticevoked potential (BAEP), AMR is the unique electrophysiological manifestation of facial spasm, the latency period is usually about 10ms, and it has auxiliary value in the diagnosis of facial spasm.
①Stimulation of the temporal branch of the facial nerve, recorded in the chin muscle.
② Stimulation of the mandibular margin branch of the facial nerve, recorded in the frontalis muscle. Square wave electrical stimulation was used, wave width 0.2ms, frequency 0.5~1.0Hz, intensity 5~20mA. EMG generally used the same core needle electrode inserted into the frontalis muscle, orbicularis oculi muscle, orbicularis oris muscle, etc., to record the changes of its motor unit. In patients with facial spasm EMG can record a paroxysmal high frequency spontaneous potentials (up to 150 times per second). BAEP can reflect the function of the entire auditory conduction pathway, mainly observing waves I, III and V. Prolonged latency indicates nerve conduction disorders. Since the source of each wave occurring is relatively clear, it is valuable for localization of the disease, and can also be combined with pure tone audiometry to comprehensively assess the preoperative vestibulocochlear nerve function.
2.Imaging assessment
MRI is important to identify the intracranial lesions that may cause facial spasm, such as tumors, AVMs, and skull base malformations, etc. MRI is also important to identify vessels that are in anatomical contact with the facial nerve, and even show the type and thickness of the vessels and the degree of compression of the facial nerve. In particular, 3D-TOF-MRA has become a routine preoperative examination for MVD, and MRI imaging based on this technique has evolved to show all vessels in anatomical contact with the facial nerve in 360°. However, it must be pointed out that the vessels shown by MRI are not necessarily the real responsible vessels, and a negative 3D-TOF-MRA is not an absolute contraindication to MVD surgery, but patients with negative 3D-TOF-MRA need to be more cautious in choosing MVD, and the patient needs to be checked again for the exact diagnosis of facial spasm, and the electrophysiological evaluation results should be referred to if necessary. If necessary, the results of electrophysiological evaluation should be referred to.
IV. Treatment
1.Medication
The commonly used drugs for facial spasm treatment include carbamazepine, oxcarbazepine and Valium. The maximum dose of carbamazepine for adults should not exceed 1200 mg/d. Alternative drugs are phenytoin sodium, clonidine, baclofen, topiramate, gabapentin and haloperidol.
②Pharmacological treatment can reduce the symptoms of facial muscle twitching in some patients.
③Facial muscle spasm medication is often used in the early stage of onset, in those who cannot tolerate surgery or refuse surgery, and as an adjunctive treatment for those whose symptoms cannot be relieved after surgery. For patients with mild clinical symptoms, significant drug efficacy, and no adverse drug reactions, long-term application is possible.
(4) Adverse reactions such as impairment of liver and kidney function, dizziness, drowsiness, leukopenia, ataxia, tremor, etc., may occur with drug therapy and should be discontinued immediately. In particular, the application of carbamazepine treatment has the risk of exfoliative dermatitis, and severe exfoliative dermatitis can be life-threatening.
2.Botulinum toxin injection
(1) Commonly used drugs: injectable botulinum toxin type A (botulinum toxinA). It is mainly used in adult patients who cannot tolerate surgery, refuse surgery, fail surgery or relapse after surgery, or have ineffective drug treatment or drug allergy. It should be used with caution when there is a decrease in efficacy or serious adverse reactions. It is forbidden to be used by allergic persons and those who are allergic to this product.
(2) DOSAGE AND ADMINISTRATION: The upper and lower lid muscles are injected at multiple points, i.e., a total of 4 or 5 points on the medial and lateral sides of the upper and lower lids or on the temporal subcutaneous orbicularis muscle of the external canthus. In case of facial or orofacial twitching, 3 injections are required in the middle, lower and cheek muscles. Depending on the condition, injections can also be given to the inner and outer brow or upper lip or lower jaw muscles. The starting dose is 2.5 U/0.1 ml per site, and additional injections can be given to those with residual spasms after 1 week of injection; the original dose or double the dose (5.0 U/0.1 ml) can be given to those with recurrence of the disease. However, the total dose of 1 injection should not be higher than 55U, and the total dose used in 1 month should not be higher than 200U.
(3) Efficacy: More than 90% of patients are effective for the initial injection of botulinum toxin, and the time for complete relief and significant improvement of spasticity after 1 injection is 1 to 8 months, mostly concentrated in 3 to 4 months, and the efficacy gradually decreases with the prolongation of the disease and the increase of the number of injections. The interval between two treatments should not be less than 3 months. If the treatment fails or the efficacy gradually decreases after repeated injections, other treatment methods should be considered. Therefore, Botox injections cannot be used as a long-term treatment for facial muscle spasm. It should be noted that the effect after each injection is closely related to factors such as the choice of injection site, the size of the injection dose and whether the injection technique is skilled.
(4) Adverse effects: A few patients may experience transient symptomatic dry eye, exposure keratitis, lacrimation, photophobia, diplopia, eyelid ptosis, reduced transience, incomplete lid closure, and varying degrees of facial palsy, which mostly recover naturally within 3 to 8 weeks. Patients with repeated botulinum toxin injections will experience permanent eyelid weakness, shallow nasolabial folds, crooked corners of the mouth, facial stiffness, and other signs.
(5) Precautions: Use with caution in patients with fever, acute infectious diseases, pregnant women and children under 12 years of age; aminoglycoside antibiotics are prohibited during the use of this product; 1:1000 epinephrine should be available for first aid in case of allergic reactions, and patients should be kept in the hospital for short-term observation after injection.
3.Microvascular decompression
(1) The hospital and the department should have the following conditions.
①Hospital should have independent neurosurgery establishment.
② Have the equipment (microscope) and instruments to carry out microsurgery.
③ CT and MRI, conditional units should be equipped with equipment and personnel for neuroelectrophysiological monitoring.
④ should be mastered by skilled microsurgery skills of senior neurosurgeons to complete.
(2) Indications for surgery.
(1) The diagnosis of primary facial muscle spasm is clear, and secondary lesions are excluded by cranial CT or MRI.
(2) The symptoms of facial spasm are serious, affecting daily life and work, and the patient is strongly willing to undergo surgery.
③Patients treated with drugs or botulinum toxin should be operated actively in case of poor efficacy, ineffectiveness, drug allergy or toxic side effects.
④Patients with recurrence after MVD surgery can be operated again.
⑤ Patients with ineffective post-operative MVD may be considered for early reoperation if the first surgical decompression is considered inadequate and if the post-operative AMR test is positive. Patients with no tendency of symptom remission or even gradual aggravation can also be considered for reoperation.
(3) Contraindications to surgery.
(1) The same as general craniotomy contraindications.
(2) Patients with severe hematologic diseases or vital organ dysfunction (heart, lung, kidney or liver).
(3) Caution should be exercised when choosing MVD surgery in elderly patients.
(4) Preoperative preparation.
(①Pre-operative examination, including functional assessment of heart, lung, kidney and liver and coagulation function, etc.
(2) MRI or CT examination of the head. 3D-TOF-MRI of the head and neurophysiological examination (AMR, BAEP, etc.) are feasible in hospitals with conditions.
(5) Anesthesia: Intravenous complex anesthesia with tracheal intubation. Except for the induction phase of anesthesia, the amount of inotropic drugs used should be controlled intraoperatively to avoid interference with neuroelectrophysiological monitoring. Total intraoperative fluid rehydration should be controlled to maintain a partial pressure of carbon dioxide of about 26 mmHg, and β-blockers should be used appropriately to facilitate surgical operations.
(6) Position: The appropriate surgical position can be selected according to the operator’s habit, usually in the lateral position with the head frame fixed. The head of the bed is elevated 15°-20°, the head is flexed forward until the chin is about 2 transverse fingers from the sternal stalk, and the shoulder girdle is pulled caudally to maintain the head in the hyperextended position, avoiding excessive pulling to damage the brachial plexus nerve, which eventually makes the mastoid root located at the highest point.
(7) Incision and craniotomy: an oblique incision in the hairline or a transverse incision behind the ear, the incision is centered 1 cm below the mastoid root, and a bone window of about 2.5 cm in diameter is formed with a grinding drill, biting forceps or milling knife, with the lateral edge to the sigmoid sinus, and the air space should be tightly sealed during the formation of the bone window to prevent the inflow of flushing fluid and blood. The sigmoid sinus should be used as the bottom edge to cut the dura mater and suspend it.
(8) Key points of microscopic operation: open the subarachnoid space to release cerebrospinal fluid, wait for the intracranial pressure to drop, sharply separate the arachnoid membrane from the caudal end of the posterior group of cerebral nerves to the cephalic end, so that the cerebellum is completely separated from the posterior group of cerebral nerves, explore the intracranial section of the facial nerve Ⅰ to Ⅳ area throughout the whole process, and when exposure is difficult, multi-angle exploration can be performed with the help of endoscopy, separate and displace all the vessels in contact with the facial nerve, and choose the appropriate method for decompression (Teflon cotton, glue adhesion or suspension, etc.). The arachnoid must be fully released intraoperatively to avoid pulling the cerebral nerve. Intraoperative AMR, myoelectric response waveform (ZLR) and BAEP monitoring should be performed in real time in hospitals where available.
There are two main bases for ending the procedure.
① Complete exploration of zone 4 of the facial nerve.
② All vessels in contact with the facial nerve have been isolated. For patients undergoing electrophysiological monitoring, complete disappearance of the AMR waveform should also be sought. For patients with persistent AMR waveforms, careful full exploration again is recommended to avoid missed vessels and to assist with facial nerve commissurotomy if necessary.
In cases of coarse vertebrobasilar artery compression, gradual separation and decompression from caudal to cephalad in the lateral aspect of the medulla oblongata can be used, with the aid of glue adhesion or suspension if necessary.
For the management of bilateral lateral myoclonus, it is recommended to choose the side with severe symptoms to operate first, and to operate on the other side at a later date according to the degree of symptom relief on the operated side and the patient’s physical condition. It is not advocated to perform bilateral MVD operations at one time, but the interval between two operations is not specifically prescribed at present.
In the reoperation of recurrent patients, more emphasis is placed on the use of neurophysiological monitoring, especially combined AMR and ZLR monitoring, to ensure adequate decompression of the facial nerve. Before reoperation in patients with ineffective recurrence, physicians need to carefully explain the risks of surgery to patients and families, and symptoms may remain unremitting or partially relieved after surgery.
(9) Cranial closure: Slowly and thoroughly flush the operative field with warm saline, start cranial closure after clear absence of bleeding, tightly suture the dura mater, repeatedly inject warm saline before closing the dura mater to expel gas, use artificial meninges and biogel closure if necessary, use autologous bone flap retraction, artificial cranial bone replacement or metal cranial plate fixation to repair the cranial defect, and close the incision layer by layer.
V. Efficacy evaluation
The criteria for determining the efficacy after facial myoclonus surgery are divided into four levels.
①Cure (excellent): Facial myospasm symptoms completely disappeared.
②Obvious remission (good): the symptoms of facial myospasm basically disappeared, only when the emotional tension and excitement, or specific facial movements only occasionally induced, the patient subjective satisfaction, the above two levels are “effective”.
③Partial remission (fair): Facial muscle spasm symptoms are reduced, but still more frequent, and the patient is subjectively unsatisfied.
Ineffective (poor): no change in the symptoms of facial spasm, or even aggravated. For patients with ineffective and partial remission, it is recommended to retest AMR, and if AMR is positive, it is recommended to operate again as soon as possible; on the contrary, if retesting AMR is negative, it is possible to follow up or adjuvant medication or botulinum toxin treatment.
Postoperative management
Postoperatively, the patient’s vital signs, consciousness, facial palsy, hoarseness, choking and vomiting should be observed comprehensively. If postoperative low intracranial pressure occurs, the patient should be placed in a flat position or in a head-low, foot-high position, with nausea and vomiting, the head should be tilted to the side to avoid misaspiration and active symptomatic treatment. If postoperative facial paralysis occurs, attention should be paid to corneal and oral care. If choking on water and swallowing dysfunction occur, avoid misaspiration. In case of cerebrospinal fluid leakage, the head should be placed 30° higher in a flat position, blockage of the nasal cavity and ear canal, flushing and drug dripping should be avoided, and the cause should be actively identified and treated properly.
VII. Complication prevention and control
1. Cerebral nerve dysfunction
Cerebral nerve dysfunction is mainly facial palsy, tinnitus, hearing impairment, and a few patients may have facial numbness, hoarseness, water choking, diplopia, etc. Acute cerebral neurological dysfunction occurs within 3 d after surgery, and cerebral neurological dysfunction occurs after 3 d after surgery is delayed cerebral neurological dysfunction, and most delayed cerebral neurological dysfunction occurs within 30 d after surgery. For example, more than 90% of delayed facial palsy occurs within 1 month after surgery, which may be related to surgical operation and postoperative cold secondary to viral infection. Therefore, it is recommended to keep warm within 1 month after surgery to reduce the occurrence of delayed facial palsy, and once it occurs, hormonal and antiviral medications should be given, and neurotrophic drugs can be applied as an adjunct.
Attention to the following operations can effectively reduce the occurrence of cerebral neurological dysfunction.
① Try to avoid electrocoagulation cauterization of the surface of the cerebral nerve and the surrounding penetrating vessels.
(2) Avoid pulling the cerebral nerve and reduce the direct stimulation of the cerebral nerve to avoid spasm of its trophoblastic vessels.
(3) Adequately dissect the arachnoid around the cerebral nerve to reduce intraoperative strain on the cerebral nerve.
④Routine intraoperative electrophysiological monitoring.
⑤ Start the use of vasodilators, hormones and neurotrophic drugs on the day of surgery.
2.Cerebellar and brainstem injury
MVD for facial spasm has a 0.1% morbidity and mortality rate, mainly due to cerebellar and brainstem injury, including infarction or hemorrhage. The key to avoid cerebellar injury is to reduce the duration and intensity of straining. The use of mannitol half an hour before surgery to reduce intracranial pressure, moderate amount of hyperventilation during surgery, bone window as close to the sigmoid sinus as possible, avoiding the use of cerebral pressure plate, gradually opening the cerebellopontine pool slowly and fully releasing cerebrospinal fluid before exploring the pontocerebellar angle can minimize the intraoperative strain on the cerebellar hemispheres, and avoiding electrocoagulation to cauterize the cerebellar and brainstem surface vessels as much as possible.
Postoperatively, blood pressure, pulse rate, respiration, and oxygen saturation were monitored continuously for 24 h by a multiparameter cardiac monitor, and changes in consciousness and pupils were closely observed. If there is a sudden increase in blood pressure and a slow pulse rate, consciousness is impaired after waking up, breathing is slow or even abruptly stopped, oxygen saturation is significantly decreased, pupils are dilated and light reflex is weakened or disappeared, cerebellar or brainstem infarction, swelling and hemorrhage should be considered, and a cranial CT scan should be performed promptly, and suboccipital decompression or extraventricular drainage should be implemented according to the CT enlargement window.
3. Cerebrospinal fluid leakage
Tight suturing of the dura is the key to prevent cerebrospinal fluid leakage; for those whose dura cannot be tightly sutured, muscle fascia can be repaired, while applying bioadhesive to completely patch the artificial dura with the dura; tightly closing the open air chamber with bone wax; strictly suturing the incision in accordance with the four layers of muscle, fascia, subcutaneous tissue and skin to leave no dead space.
If cerebrospinal fluid nasal leakage occurs, immediately tell the patient to lie down with the pillow removed, tell the patient not to pick, dig or block the nostrils, keep the nostrils clean, observe the change of body temperature, and use antibiotics to prevent infection. If necessary, use dehydrating agent or lumbar pool drainage to reduce intracranial pressure. If the leak does not heal for a long time or recurs several times, repair of the leak is needed.
4.Low intracranial pressure syndrome
It may be caused by prolonged exposure of the surgical site, release of large amount of cerebrospinal fluid and reduction of cerebrospinal fluid secretion after surgery. It often manifests as headache, dizziness, nausea and non-jet vomiting, as well as low blood pressure and accelerated pulse rate, and the symptoms can be relieved after lowering the head position. During surgery, the dura mater should be filled with saline when sutured to expel air. Take a flat position after surgery.
5.Other complications
MVD surgery should be operated strictly to avoid complications such as infection, poor wound healing, balance disorder, incision pain, distant septal site hematoma and vertebral artery injury. Some patients develop vertigo after surgery, most of them are found during postoperative activities, the symptoms vary in severity, the severe ones affect activities and can be gradually reduced, mostly relieved within 1 to 2 weeks, a few patients can last for more than 1 month, but do not affect activities.