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Microsurgery and Neuromodulation for Facial Spasms
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.302455
Keywords: Blepharospasm, hemifacial spasm, microvascular decompression, neuromodulation, oro-mandibular dystonia
Facial spasms are muscle spasms associated with motor components of facial, trigeminal or hypoglossal nerves. Hemifacial spasm (HFS) is a rare disorder characterized by tonic-clonic or myoclonic contractions of facial muscles. It follows a characteristic pattern of progression, starting with the orbicularis oculi. Primary HFS is commoner in women, with onset in the fifth to sixth decades.[1] The vast majority of cases are unilateral, with bilateral cases comprising only 1%. The left side is more commonly affected.[1],[2] Younger age (<40 years) at onset indicates the presence of underlying disease conditions, most commonly Multiple Sclerosis. Aetiologically, it may be classified as primary or secondary, and clinically as typical or atypical. Numerous interventional modalities are now available for treatment. Microvascular decompression (MVD) remains the most definitive, effective and lasting treatment modality for primary typical cases. Other facial spasms are essentially focal dystonia. The dystonia of upper face predominantly involves eye and is called blepharospasm. Dystonia of lower face predominantly involves jaw and mouth and are called oromandibular dystonia (OMD). After medical management and Botulinum toxin fails, neuromodulation in the form of deep brain stimulation is an effective treatment.[3],[4]
HFS was first described by Schultze in 1875, who discovered a vertebral artery aneurysm compressing the root exit zone (REZ) at autopsy.[5] HFS was first mentioned in English literature by Gowers in 1888, who delineated it from other aetiologies of facial spasm.[6] Gardner and Sawa in 1960 first reported that the condition can be reversed with treatment,[7],[8] performing neurolysis, with a few cases of vascular loop translocation. Peter Jannetta further developed the concept of vascular cross compression for various cranial rhizopathies in the microsurgical era, and popularised the procedure of MVD in the treatment of HFS.[9]
Primary HFS is defined as an entity without any underlying disease. The cause is most commonly observed to be compression or distortion of the nerve root by an aberrant vascular loop. The offending vessels found are – anterior inferior cerebellar artery (AICA), posterior inferior cerebellar artery (PICA), vertebral artery (VA), basilar artery (BA), or veins, in descending order of frequency. Around 20% of cases show multifocal compression or a combination of compressing vessels.[10] The arteries progressively lengthen with age, and become more tortuous, thus impinging on a variety of nerve roots in the subarachnoid space.[1],[11] Thus, primary HFS is a progressive disease of old age, and rarely remits spontaneously. Secondary HFS may be caused by a variety of pathologies, divided into compressive (CP angle tumor, vascular malformation, bony tumor or petrous bone fracture, cholesteatoma), or non-compressive (stroke, multiple sclerosis, basilar meningitis, post-paralytic (e.g. Bell's Palsy) facial synkinesis). The mechanism has been found to be demyelination of nerve axons at the REZ, also called Obersteiner-Redlich Zone, due to chronic compression or irritation, leading to hyperexcitability of axons. Ephaptic transmission of impulses occurs due to abnormal excitation of surrounding demyelinated axons by an action potential conducted from a single axon. This is analogous to the mechanism behind trigeminal neuralgia. Compression at a point distal to the REZ can also produce similar effects. Rare cases of intraparotid involvement of the nerve, producing HFS, have also been described.[12] A central hypothesis of HFS is also proposed, involving hyperexcitability of neural circuits at the facial nucleus or supranuclear levels. This may be a direct consequence of the neurovascular conflict.[11]
The patient presents with spontaneous sudden facial spasms resembling myoclonus. The spasm is usually synkinetic, i.e., all involved muscle groups contract at the same time. The frequency of contraction is irregular and non-rhythmic. The presence of concurrent neurological deficits indicates a secondary cause for HFS, or presence of HFS as part of a wider syndrome. The spasms may be worsened by emotional states and stress[8] and typically persist even in sleep.[1],[13] In later cases, spasms may be precipitated by facial movements such as eating, speaking etc., correlating with the appearance of electromyographical lateral spread response (LSR).[14] The presentation may be categorized as typical or atypical. The typical variety is characterized by onset in the lower palpebral muscles, then the rest of the orbicularis oculi, followed by the orbicularis oris, buccinator and platysma. The reverse sequence is referred to as atypical HFS. It constitutes only about 2-10% of all cases.[15] The difference is attributed to the topographical organization of facial nerve fascicles and the site of compression. Posterior-rostral compression of the nerve affects the lower facial muscles, resulting in atypical HFS, whereas anterior-caudal compression results in typical HFS. The patient may complain of difficulty in binocular vision due to intermittent closure of the involved eye. This may disturb daily tasks such as driving, reading, crossing a road etc., Rarely, patients may also complain of hearing a clicking sound in the ear, attributed to contraction of the stapedius.[1] The patient may try to consciously inhibit eye closure, in an attempt to overcome the blepharospasm. This may rarely result in dry-eye on the contralateral side.[16] Around 37% of patients with HFS have concurrent systemic hypertension, which seems to be more commonly associated with left-sided HFS.[17] The disease is relentlessly progressive. Spasms which may start as transient and clonic, progress to become sustained and tonic.[1],[13]
Early cases may be difficult to distinguish from neuromuscular disorders and in such cases, EMG studies can be most helpful to confirm the diagnosis by providing the following findings[18]:
MRI is the modality of choice. Vascular loop impingement may be visualized using a combination of two techniques :
MRI findings correlate well with intraoperative observations, with a sensitivity of 97% and a specificity of 100% according to several studies.[19] Although it is not necessary to prove neurovascular conflict before surgery, secondary causes such as mass lesions and vascular malformations along the pathway of the nerve need to be ruled out.
Botulinum toxin injection is the initial choice of management in patients with confirmed HFS.[1] Medical management with anticonvulsant drugs is reserved for those who refuse, or cannot tolerate Botulinum toxin, and in mild cases. It may be used as a bridge therapy, till definitive management can be carried out. Surgical management is considered for primary HFS only when the patient finds the condition to be severely limiting their lifestyle or HFS becomes refractory to other modalities. Medical fitness for surgery must be carefully considered. Treatment of secondary HFS is specific to the underlying cause.
Botulinum toxin is a safe and effective treatment of HFS.[20] Type A toxin is preferred in HFS. It is injected using EMG guidance. It produces pre-synaptic blockade of neuromuscular electrical transmission. The effect lasts for 3–6 months. It ablates the muscle spasms, but does not tackle the underlying pathology of neural irritation. Thus, although spasms are no longer visible, the patient may continue to feel the sensation of spasm.[21] It may produce minimal local adverse effects due to injection. Adverse effects of muscle relaxation such as facial asymmetry, ptosis, and diplopia are usually transient. Some patients may also experience excessive lacrimation or dry-eye. Over a period of time, patients may develop neutralizing antibodies, thus diminishing the efficacy and duration of effect of botulinum toxin. Repeated injection sessions may also be unappealing to many patients. The high cost of treatment limits its widespread applicability, especially in developing countries.
A variety of antiepileptic medications[22],[23] may be used in primary HFS, and in non-compressive causes of secondary HFS. They may also be used in compressive type of secondary HFS till definitive treatment is carried out. Carbamazepine is the agent of choice.[24] Carbamazepine has also been combined with botulinum toxin injections to produce better efficacy.[25] Baclofen[26] and benzodiazepine drugs may also be used. Dose requirements usually increase over the course of the disease, until finally a state of drug refractoriness may be reached, or the adverse effects of the drug become intolerable.
Microvascular Decompression surgery is the only definitive management of HFS. The aim of the procedure is translocation of the offending vascular loop away from the pathway of the nerve, thus allowing for repair and remyelination of the nerve fascicles. Posterior fossa craniotomy and exploration usually reveals an offending vascular loop even in cases not detected on MRI. Complete exploration of the subarachnoid course of the nerve increases the chance of success of surgery.[27] We usually perform the procedure in supine position with head turned,[28] a modification of the position described by Sugita for CP angle exposure.[29],[30] The Retromastoid incision exposes the transverse -sigmoid junction and an area 2 cm below it. After durotomy, the procedure consists of careful arachnoidal dissection of the cisterns around the middle neurovascular complex (CN VII, VIII, and AICA), confirmation of the area of conflict, followed by transposition of the vascular loop [Figure 2]. LSR may be monitored intraoperatively, using facial nerve EMG.[14] A ball of teased Teflon material is gently inserted in the angle between the nerve REZ and the vessel, sealing it in place with fibrin glue.
Complications of MVD: Dissection of the vessel away from the nerve, especially a meatal loop of AICA lodged between the roots of CN VII and VIII may result in transient facial paresis. The AICA loop also supplies numerous perforating branches to the brainstem, and inner ear. Care must be taken to ensure that these small perforators are not avulsed during vascular transposition. This is the reason why vascular transposition may prove more difficult in elderly people. Sensorineural hearing loss is a frequent complication of this procedure and can be avoided by gentle cerebellar retraction without lateral stretch.[31] Brainstem Auditory Evoked Response (BAER) monitoring is recommended.[2],[31] A small but significant risk of serious complications remains, including posterior fossa hematoma, CSF leak, brainstem infarct, permanent disability or even death.[32] Postoperative hypertension may be observed in patients in whom high volume of material is tightly packed at the interface with the brainstem.[2]
Botulinum toxin injection was found to have a high success rate of 70-90%.[20] The limiting factor was the need for repeated injections and the eventual development of resistance. Botulinum toxin B may be used in patients resistant to toxin A. MVD produces long term resolution rates of around 95%, with 83% showing significant improvement and 12% showing partial improvement. Resolution of spasm may follow various patterns – immediate postoperative disappearance delayed gradual resolution, or disappearance followed by reappearance followed by gradual resolution.[33] A majority of patients experience immediate resolution of spasm postoperatively.[34] Success rates are especially high when a definite aetiological factor is found, and when complete exploration of the cisternal segment of the nerve is carried out. Failure rates are around 5-10%.[35] Re-operation with complete exploration may be considered in patients with no response to surgery. Success rates of reoperation are good. Persistence of LSR on EMG after surgery is a poor prognostic factor, indicating either incomplete decompression of the nerve, or failure of remyelination.[14] Lesional excision in cases of secondary HFS also have very high rates of resolution. Outcome in patients undergoing MVD surgery is not affected by previous Botulinum toxin injections.[36] MVD produces resolution of hypertension associated with HFS, and may cause reduction in systolic BP in normotensive patients.[17]
HFS may be confused with numerous close mimics. However, it can be reliably distinguished from these on the basis of history, clinical evolution, and pattern of manifestation.[37] Focal facial seizure – may be difficult to differentiate an attack. However, the history and pattern of evolution of HFS is characteristic. Focal seizure may be followed by transient weakness. EEG serves to establish a definite diagnosis.[38] Hemimasticatory Spasm – similar to HFS, but involving muscles of mastication, predominantly the masseter.[39] More responsive to medical management than surgery. Myoclonus, Chorea – Myoclonus may occur due to pathology at the level of the cortex, basal ganglia or brainstem, while chorea occurs due to pathology at the level of basal ganglia. These may be distinguished from HFS by the presence of systemic involvement, specific history, and associated neurological signs.[37] Tics – these are repetitive semi-purposeful unsustained stereotyped movements of a group of muscles, often in response to a premonitory sensation.[40] They most commonly involve blinking and facial twitching.[41] However, in contrast with HFS, these tics are suppressible.[42] Facial Myokymia – this appears as a worm-like twitching or rippling of small muscle fibers under the skin.[43] EMG is diagnostic. Most cases are idiopathic, with some being caused by brainstem lesions. Most cases are self-resolving, the rest require medical treatment.
These are idiopathic, non-hereditary, focal dystonia syndromes. They are always adult-onset and more commonly seen in females. Blepharospasm when combined with OMD is called Meige's syndrome.[44] OMD could be either jaw opening dystonia, jaw-closing dystonia or tongue and pharyngeal dystonia. Jaw opening dystonia (JOD) is an extremely disabling and uncommon entity. In 1976, Marsden coined the name Brueghel × s syndrome for adult-onset oro-mandibular dystonia with or without blepharospasm.[45] Jaw opening dystonia is an unusual neurological disorder characterized by a sustained contraction of the lateral pterygoid muscles, resulting in the protruding open-jaw. A small number of cases have been reported in the literature of this adult-onset isolated JOD.[45],[46],[47],[48],[49] Cranial dystonia has a slow progression. Initially, it may only be associated with movements or tasks like mastication or blinking. It is localized to a region and does not progressively recruit other regions. Over time the symptoms become more severe. Blepharospasm progresses from increased blinking to inability to keep the eyes open. Tongue dystonia pushes the tongue out of mouth with darting movements of tongue and inability to eat. These patients often need percutaneous endoscopic gastrostomy (PEG) to treat the malnutrition. OMD can progress from subtle jaw movements, chewing problems, mild speech changes to inability to open or close the jaw. Apart from the motor disability, these patients face social isolation due to the visibility of the disorder.
Pathophysiology of this disorder is also not clear. Basal ganglia dysfunction is the commonly accepted hypothesis.[50],[51],[52] Basal ganglia dysfunction has been variously attributed to striatal dopaminergic preponderance,[52] pallidal hyperactivity,[50] and an idiopathic form of cholinergic receptor hypersensitivity in the basal ganglia.[53] Pontine dysfunction[51] and peripheral causes[54] have also been proposed. Recent reports of successful pallidal deep brain stimulator (DBS) placement for treatment of this condition suggest pallidal etiology.[55]
Treatment of cranial dystonia is challenging primarily due to diagnostic difficulties. Oftentimes it is confused with psychosomatic disorders, temporomandibular dysfunction, primary ophthalmic problems or hemifacial spasms. The severity of these problems varies significantly and hence it is unusual to see a patient in the early stage. Once accurately diagnosed, first line of treatment is medical management. Medical management is limited to medications like tetrabenazine, lithium, clonazepam and trihexyphenidyl.[56] Botulinum toxin injections of lateral pterygoids, masseter,[57] temporalis, orbicularis oculi are successful in treating this disorder but have a transient benefit that often reduces with time.[58],[59]
Bilateral Globus pallidus internal (GPi) deep brain stimulation (DBS) helps in intractable cases of cranial dystonia.[4],[55],[60] Pallidal DBS has been shown to be successful in treating this disorder with a 72% improvement at 6 months.[55] The patient selection is based on intractability of the disorder, disability caused by it, clear neuropsychological evaluation and patient's understanding of the procedure and outcome. The GPi DBS needs to be bilateral, it takes up to a few months to a year to see the benefits and in our experience, the average benefit is 50%.[61],[62]
The surgical technique is similar to other indications of DBS and involves the stereotactic placement of bilateral intracranial lead placement and sub-clavicular IPG placement.[61],[62] Planning is done using Magnetic resonance imaging (MRI) with gadolinium-enhanced T1-weighted volumetric sequence, T2-weighted axial and inversion recovery (IR) sequence. Optic tract is a surrogate for GPi target. Anterior commissure, posterior commissure (AC-PC) co-ordinates for GPi are 19-21.5 mm lateral to the midline, 2-4 mm anterior to the midcommissural point and 3-4 mm ventral to AC-PC plane [Figure 3]. The trajectory avoids any vessels, sulci and ventricular wall. The actual procedure can be done with a stereotactic frame or frameless.[63] If patient can tolerate an awake procedure, physiological mapping is done. If patient is unable to tolerate or if there are airway concerns, image guided targeting is done with equal accuracy.[64] Physiological mapping of GPi target typically shows striatum initially with minimum neuronal activity, followed by regular border cells, followed by characteristic bursting and pausing cells in globus pallidus externus (GPe) followed by increased background activity and tonic and bursting firing in GPi and most ventrally phosphenes elicited due to optic tract stimulation.[65],[66] After the bilateral leads are placed in the GPi target, implantable pulse generator (IPG) is implanted in the sub-clavicular area and connected to the leads using extensions.
Ventral contacts yield best response during programming of the GPi DBS.[4] On average 50%–70% benefit in symptoms is seen in carefully selected patients with well-placed leads and optimum programming.[55],[61],[62] Complications of DBS are rare and include intracranial hemorrhage, infection, and hardware malfunction.[60]
Facial spasms are a diverse group of disorders. They are rare but debilitating and lifestyle limiting disorders. Treatment benefits and outcomes depend on accurate diagnosis. Careful clinical evaluation and detailed appropriate imaging are necessary to establish the diagnosis and underlying cause. Management should be tailored as per the specific case, and yields good outcomes in properly selected patients. Acknowledgement NIL Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3]
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