Secondary Masticatory Muscle Spasm
Occasionally the jaw closers or jaw openers can develop a continuous strong spastic activity which if sustained for a long period of time, will actually produce contracture with substantial shortening of the muscle. Often this activity is secondary to another acute disease process (trauma or infection), although it can also be seen as a primary idiopathic dystonic process.
Proposed Mechanism
There are several conditions which might produce a secondary masticatory muscle spasm, including radiation of the facial tissues, spasms in association with multiple sclerosis, scleroderma, progressive supranuclear palsy, amyotrophic sclerosis, and vascular abnormalities. If the spasm is unilateral the clinician must consider hemi-masticatory spasm and focal dystonia. Often patients with spasm have a reduced opening and the clinical challenge is to determine how much of the reduced opening is due to muscle contracture and how much is due to active contraction or some other cause. [1], [2], [3]
Treatment
Certainly the approach to secondary spasm is to identify the cause if possible. For example, if the spasm is due to a traumatic injury of the temporomandibular joint, then treatment of the pain and inflammation in the joint and using an anti-spasmotic agent to suppress the motor reaction until healing occurs would be the best approach. [4]
For those spastic conditions that are not acute, self-limiting problems once local or CNS pathologies are ruled out, one approach is to use BoNT-A injections to suppress the activity. Several case reports describe BoNT-A use in patients with long-standing spasms of the jaw. [5] BoNT-A has been used to manage secondary trismus due to radiation of the facial tissues. [6] It has also been reported to be successful in managing trismus in a patient with amyotrophic lateral sclerosis who exhibited spastic contraction of the jaw. [7]
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Hemi-facial Spasm
Episodic hyperkinetic spastic contractions can affect the unilateral facial muscles. It will start with an intermittent periorbital twitching, usually of the inferior orbicularis oculi muscle. Over months to years this abnormality can progress to involve half of the face and the platysma muscle.
The muscles of mastication are not involved as this is a disorder of cranial nerve VII. Sometimes these twitching movements may progress to a sustained, chronic contraction of the involved facial muscles. [8]
When the muscles innervated by the facial nerve undergo a sudden, unilateral, synchronous contraction, this is called hemi-facial spasm. These spastic actions may be brief or may persist as a tonic contraction of several seconds’ duration and may occur many times a day. The main problem with this disorder is social embarrassment, but if the spastic contractions are strong, they may also cause pain.
Hemi-facial Treatments
The hemi-facial spasm could be secondary to a compression to the facial nerve at the root zone, local demyelination, ephaptic transmission of impulses or hyperexcitability of the facial motor nucleus due to irritation from peripheral lesion of the nerve. [9]
It may be primary (mainly attributed to vascular compressions of the seventh cranial nerve in the posterior fossa) or secondary to facial nerve or brain stem damage. [10]
The condition might be treated with medications, botulinum toxin and surgery.
1. Oral Medications
The efficacy of oral medications in hemi-facial spasm is often transient and the drugs most commonly used are anticonvulsants (such as carbamazepine and oxcarbazepine), anticholinergics, baclofen, and clonazepam. [11], [12], [13] Gabapentin for the treatment of hemi-facial spasm has been reported in several open-label trials to have moderate success. [14]
2. Botulinum Neurotoxin (Botox) Injections
The standard medical management for HFS is botulinum neurotoxin (BoNT) injections, which provides low-risk but limited symptomatic relief. [15] A review of the literature on botulinum toxin treatment in hemi-facial spasm showed that there have been numerous open-label studies and a few double-blind placebo-controlled studies with high success. [16]
Adverse effects include dry eyes, ptosis, eyelid and facial weakness, diplopia, and excessive tearing. Overall these effects are transient and no serious long-lasting effects have been reported. [17]
3. Microvascular Decompression
Microvascular decompression (MVP) is an effective curative method for almost all the patients affected with primary HFS. [18] The most common vessel causing compression of the facial nerve is the posterior inferior cerebellar artery. This vessel must be sharply dissected free from the arachnoid and mobilized laterally away from the nerve so that a Teflon implant can be placed.
In cases of atypical hemi-facial spasm, the pathological vascular entity is almost always located rostral to the nerve or between the seventh and eighth nerves. [19] MVP surgery does have a recurrence rate of up to 20% and complications include aggravation of preexisting hearing loss and mild facial weakness. [20]
Hemi-masticatory Spasm
An unusual analog to the disorder of hemi-facial spasm is called hemi-masticatory spasm (HMS). The latter condition has characteristics (unilateral episodic, short lasting spastic contractions), which are virtually identical to the former, with the only difference being that hemi-masticatory spasm is essentially a spastic contraction of the masseter and temporalis muscles on one side of the face. [21] It presents as an intermittent temporalis or masseter contraction, which increases rapidly becoming severe & often painful.
Proposed Mechanism
Since this is a disorder of the motor branch of the fifth cranial nerve, the muscles of facial expression are spared. If severe, it may move from an episodic event to a sustained, chronic contraction of the involved jaw muscles. It is also likely that this condition involves the medial pterygoid, in most cases, but this is not clearly documented.
The clinical and neurophysiological findings in a case of hemi-masticatory spasm (HMS) in a single patient followed during a 14 year period after initial diagnosis showed that the clinical symptoms remained unchanged throughout the period of observation. [22]
The use of surface electromyography demonstrated irregular bursts of motor unit potentials in a patient with hemi-masticatory spasm and masseter muscle hypertrophy, even with a normal muscle biopsy. These results indicated that the contraction was related with ectopic discharges of the trigeminal nerve. [23]
Hemi-masticatory Spasm Treatment
Since the mechanisms for hemimasticatory spasm remain unclear, an efficient treatment strategy still needs to be developed, however, there are reports of management with BoNT-A and surgical approaches.
1. BoNT-A Injections
The first successful use of BoNT-A for hemi-masticatory spasm was reported on a single case of hemi-masticatory spasm. [24] HMS may have a peripheral origin, with dysfunctional contractions of the masseter muscle, hence the application of botulinum toxin injections into the affected muscle reduces the spasms. [25]
2. Surgery
A surgical technique of microvascular decompression of the trigeminal root has been used to separate the superior cerebellar artery and the motor branch of the trigeminal nerve root. To assure separation, pieces of soft wadding are interposed between the nerve and the vessel. [26], [27] If the spasms are produced by a vascular compression, a MVD surgical is a logical approach, however, control studies with large samples are needed before this technique is widely accepted as first line for HMS. [28]
Related Reading: Surgical Management for Oromandibular Dystonia
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References
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