Peripheral movement disorders

Introduction

Abnormal involuntary movements (dyskinesias) usually are caused by brain damage or dysfunction. Occasionally, however, lesions of the spinal cord, spinal roots, cervical or lumbar plexus, or even peripheral nerves appear to cause a variety of dyskinesias ( Table 26.1 ). Sometimes the relationship between the trauma and the movement disorder is not definite, and there are no proven rules to relate them. Jankovic and colleagues have proposed some criteria that can be used as guidelines while waiting for more definitive rules ( Table 26.2 ) ( ; ). An example of a definitive peripheral disorder is hemifacial spasm, in which compression of the facial nerve by an aberrant vessel or cerebellopontine angle mass lesion in the posterior fossa produces repetitive clonic and tonic contractions of one side of the face. Focal myoclonus is sometimes the result of damage to spinal roots, the plexus, or peripheral nerves. Such lesions also rarely cause other dyskinesias, such as dystonia and other forms of muscle spasms, sometimes associated with complex regional pain syndrome. Pathophysiologically, a peripheral injury may act as the trigger for the appearance of dyskinesias thought to arise in the brain; the peripheral injury alters central nervous system (CNS) activity to generate involuntary movements.

Hemifacial spasm

Hemifacial spasm (HFS) is a rare condition that is more frequent in women than men and may be more common in Asians compared to Whites ( ), characterized by synchronous spasms of one side of the face. It is more frequent in women than men ( Table 26.3 ). Most cases are primary, but some are secondary after recovery from facial nerve paresis ( ; ). The spasms are usually very brief, but can occur in runs and are occasionally tonic. The disorder typically begins around the eye, and this often is the most symptomatic aspect to the disorder ( Fig. 26.1 ) ( Video 26.1 ). The disorder can be bilateral, but then the two sides of the face do not spasm in synchrony. Cases seem to be more common in persons of Asian origin ( ; ). Twitching is mostly spontaneous and can be brought out by facial muscle contraction. When someone closes the eyes, ordinarily the brow moves down, but in hemifacial spasm, the brow moves up because of the synergistic involvement of the frontalis muscle. This is known as the “other Babinski sign” ( ), and it is a reliable diagnostic feature ( ; ). The differential diagnosis includes synkinesis after Bell palsy, stroke, demyelination, psychogenic, tic, myoclonus, parotid gland tumors, Chiari malformation and posterior fossa anomalies, and hemimasticatory spasm ( ; ). The distinction among these usually can be made using electromyography ( ) and magnetic resonance imaging. The latter is recommended for the assessment of HFS ( ).

Video 26.1. Hemifacial spasm.

The disorder clearly involves the facial nerve, and the cause appears to be most frequently (94%) a compression of the nerve by a blood vessel just as the nerve leaves the brainstem ( ; ). About 4% of cases are due to a tumor compressing the nerve ( ). Biopsy of the compressed nerve shows demyelination.

Definitive treatment can be by surgery to decompress the nerve ( ; ; ; ). This procedure of posterior fossa microvascular decompression was initially developed by Peter Jannetta and is often referred to as the Jannetta procedure ( ). The vessels most frequently implicated are the posterior inferior cerebellar artery and the anterior inferior cerebellar artery. The vertebro-basiliar artery has been implicated in a small percentage of cases (Mercier, 2018). In this procedure, the offending artery is transposed away from the cranial nerve exit zone, thus alleviating the pressure on the nerve. In a retrospective studies, approximately 75%-85% ( ) of patients with HFS have complete resolution, and improvement occurred in 16%. The features that most predicted a good outcome included male sex, mild HFS, indentation of the facial nerve, and delayed, reversible facial palsy (Lee, 2019). The adverse effects of the procedure include hearing loss and permanent facial nerve palsy (Bartindale, 2018). There are some reports of improved efficacy and reduced adverse effects using endoscopic guidance ( ; ). Given the risk of permanent side effects, most patients prefer botulinum toxin treatment, which can be highly effective and can improve quality of life without the risk for permanent sequelae ( ; ; ; ; ; ). The dose of botulinum toxin is typically very low but improves symptoms in approximately 85% of patients ( ) although there is an absence of randomized controlled clinical trials ( ). In some patients receiving botulinum toxin unilaterally for HFS, facial asymmetry can be cosmetically unacceptable. These patients can benefit from bilateral injections to reduce the asymmetry (Xiao, 2018). With the lower doses used in HFS, the occurrence of neutralizing antibodies is rare ( ).

Although the cause is relatively clear, the pathophysiologic processes are still not certain. There are two main hypotheses, and there are good data to support each.