The other Babinski sign: a brief review of hemifacial spasm

Joseph Babinski is famous for his 1896 description of the Babinski sign, an abnormal plantar reflex associated with dysfunction of the pyramidal system. He is less well-known for his “other” Babinski sign: paradoxical raising of the eyebrow associated with closure of the eye, a feature typical of hemifacial spasm. As Babinksi noted in 1905, hemifacial spasm (HFS) is a disorder of painless, involuntary facial twitches confined to the muscles supplied by the facial nerve. While benign, it causes significant morbidity due to excessive closure of one eye, and the social effects of an abnormal appearance. Unfortunately, facial twitches are often attributed to stress or anxiety, leading to a delay in diagnosis. A vigilant search for organic causes is essential when these symptoms arise, as highly efficacious treatment options for HFS are available and can significantly improve quality of life. HFS occurs more commonly in females (2:1) and has an overall prevalence of approximately 10/100,000. 1 The orbicularis oculi is the site of onset in the large majority of cases. Over months to years, the disease spreads to other muscles. 2 Spasms are described as clonic or tonic, are aggravated by stress, fatigue and anxiety, and persist during sleep. Disease is usually unilateral, and spasms are synchronous in all affected ipsilateral muscles. 2 Bilateral disease occurs in a small minority of cases, and spasms are never synchronous bilaterally. In most cases, hemifacial spasm is due to arterial compression of the root exit zone (REZ) of the facial nerve. This is similar to the proposed mechanism of trigeminal neuralgia, in which the trigeminal nerve is compressed in the REZ, causing demyelination and recurrent episodes of intense pain. In much the same way, compression of the facial nerve causes spontaneous irregular discharges, leading to involuntary muscle contractions. As well, nonsynaptic neural transmission (ephapsis) between branches of CN VII may occur, causing synkinesis. Most commonly, the aberrant artery is the posterioinferior cerebellar artery (PICA), the antero-inferior cerebellar artery (AICA), or the vertebro-basilar artery (VB). In one series, these vessels were responsible 61%, 56% and 27% of the time, respectively. The same study found that multiple vessels were responsible 40% of the time. However, up to 25% of the population has vascular loops compressing CN VII, suggesting that this alone is insufficient to produce HFS. Vascular loop decompression surgery via the posterior cranial fossa is very effective in providing relief from spasms. For some patients, relief is almost immediate, while for others it can take up to a year following surgery to see the full effects. This delayed cure suggests that HFS is not only due to mechanical compression. Demyelination of the nerve from the brainstem and hyperexcitability of the facial nerve nucleus due to irritation from neurovascular compression may play a role. The slow reversal of these plastic changes explains the delay. Several other diagnoses can present in a similar fashion, including benign essential blepharospasm (BEB), focal motor seizures, and craniofacial tremor. These are differentiated largely based on clinical presentation, so a careful history and physical exam are essential. For example, BEB often presents with spasms of the orbicularis oculi and adjacent muscles, which may be difficult to distinguish from HFS. However, BEB is often associated with eye irritation, vague ocular pain and photopobia. If the facial spasms are associated with body tremor, or a family history, craniofacial tremor is more likely. Focal motor seizures are implicated when post-ictal weakness and a greater involvement of the lower face are present. If the clinical presentation is ambiguous, electrophysiologic studies and imaging can aid in the diagnosis. The characteristic sign of HFS on electrophysoiologic studies is a response in distant facial nerve branches following a stimulus to a single branch. This can be seen, for example, by spread of the blink reflex on stimulation of the supraorbital nerve to muscles other than orbicularis oculi. This is referred to as lateral spread response (LSR) and is attributed to spread of excitation at the site of ephapsis. Rarely, HFS is caused by tumors, arteriovenous malformations, and venous compression. Because the risk of tumor is low, imaging may not be cost effective when the diagnosis is clear. However, a careful neurologic exam for focal signs is essential, and imaging is suggested if these are present or if conservative management fails. 2 Advanced MRI techniques, such as constructive interference in steady state, are effective at identifying neurovascular contact. Imaging may also assist in surgical planning. While spontaneous remission of symptoms is possible, it occurs in less than 10% of patients, and significant effects on quality of life usually demand intervention. Several oral medications have been studied, including carbamazepine, anticholinergics, baclofen, clonazepam and haloperidol. However, sample sizes have been small and it is difficult to confidently interpret the results. The effects of oral medications are usually transient, and unacceptable side effects often occur. For many patients, this is not a viable treatment option. In contrast, many physicians consider botulism toxin (BTX) to be the treatment of choice. While few double-blind randomized studies evaluating BTX for HFS exist, the available evidence is encouraging. Park et al described an open-label study of 101 HFS patients, 98.6% of which had excellent results after injection of botulism-A. The mean duration of effect was 16.5 weeks, with a range of 11-40 weeks. In a review of the HFS-BTX literature, Jost et al found a total of 37 open case-control studies (N=2295) in