Introductory Chapter: Bell’s Palsy

1. Introduction

The seventh cranial nerve, commonly known as the facial nerve, is a compound nerve having motor, parasympathetic, and sensory components. Its motor portion innervates muscles for facial movement and expression. In addition, it is involved in taste over the anterior two-third of the tongue. Its parasympathetic component supplies secretomotor fibers to submandibular and sublingual salivary glands and the lacrimal gland. A small twig of this nerve carries sensations from the pinna and the external auditory meatus.

Facial paralysis is a common clinical condition that significantly impacts a patient’s quality of life [1]. Seventh cranial nerve paralysis has been categorized as supranuclear if the lesion is above its nucleus in the pons and as intranuclear if the lesion is below the nucleus. This categorization is important from diagnostic, therapeutic, and prognostic points of view and must be made clinically at the initial presentation itself. The peripheral facial nerve palsy, popularly known as Bell’s palsy, is an acute disorder of the facial nerve, which produces full or partial loss of voluntary movement on one side of the face. Less common features are loss of taste sensation over the ipsilateral half of the tongue, hyperacusis, tingling or numbness of the cheek/mouth, and ocular pain.

2. Historical perspective

James Douglas (1675–1742) in the eighteenth century gave the description of unilateral facial paralysis. However, Cornelis Stalpart van der Wiel in 1683 first clearly observed and recorded a case that was later described as Bell’s palsy. Sir Charles Bell (1774–1842), Scottish surgeon anatomist, and First Professor of Anatomy and Surgery at the Royal College of Surgeons, London, is credited with the first authentic description of the anatomy of the facial nerve and its association with the idiopathic peripheral facial palsy in 1821 [2].

3. Emotional vs. volitional facial paresis

Perhaps the most difficult and poorly understood component of facial palsy is the distinction between voluntary and emotionally driven facial expressions. It must be appreciated that human facial emotional expression is a complex phenomenon resulting from the summation of activity of a large-scale neural network in the cerebral cortex [2]. Gower’s description provides an early description of a clinical dissociation between voluntary and emotionally driven facial expressions [3, 4]. Emotional facial paresis results in impaired activation of face muscles with emotion but normal voluntary activation. In contrast, volitional facial paresis such as Bell’s palsy results in facial weakness on voluntary effort while emotional movements are preserved [5].

4. Diagnosis

A diagnosis of Bell’s palsy is essentially a clinical one and is based on the exclusion of potential other causes of facial weakness. Thorough clinical evaluations suffice in most cases, and they do not require elaborate investigations. Risk factors for Bell’s palsy include pregnancy, preeclampsia, obesity, hypertension, diabetes, and upper respiratory ailments. The etiology, prognosis, and degree of facial paralysis are quite variable, and it is not possible to draw a treatment plan which fits to all [1, 6]. Thus, we must exclude other causes of facial palsy in the first instance.

MRI studies are needed on the suspicion of intracranial lesions such as tumors, stroke, and demyelination [7]. The role of electrophysiological tests such as nerve excitability test, maximum stimulation test, electroneuronography, electromyography, etc., though limited in diagnosis, is recommended for assessing regeneration of the nerve and synkinesia.

5. Prognosis

In most instances, patients with Bell’s palsy recover completely within approximately 6 months without any treatment [8]. However, 20–30% of patients will have residual facial paresis and disfigurement. Half of such patients (approximately 10–15%) will have moderate-to-severe sequelae such as dysarthria, hemifacial spasm, abnormal lacrimation while eating (crocodile tears), contractures, and synkinesis. In general, children have better outcomes [9]. It has been observed that patients with axonal nerve injury have poorer recovery than those with demyelination. Electrophysiological studies may help us in identifying such subjects.

6. Treatment

To achieve a good cosmetic, and functional recovery, reduction of neuronal damage and prevention of sequel, medical management for Bell’s palsy can be categorized into two, i.e., pharmacotherapy and physiotherapy [8]. Surgery is rarely an option for the management of Bell’s palsy.

Till recently, corticosteroid was the only drug in our armamentarium to tackle Bell’s palsy. Because of their anti-inflammatory mode of action, they can reduce edema and inflammation of the facial nerve. American Academy of Neurology guidelines stated that steroids are highly effective in recovery of facial nerve function in new-onset Bell palsy [10]. Now we have antiviral therapy, which has improved the outcome. Commonly used antiviral agents are acyclovir, famciclovir, and valaciclovir [1]. They can be given concurrently with steroids. The Cochrane review concluded that a small but just significant benefit of combination therapy compared with corticosteroids alone in severe Bell’s palsy [11]. To achieve better results, treatment with steroids and antiviral drugs should be initiated at the earliest, preferably within the first week of symptom onset.

Physical therapy, such as exercise, massage, biofeedback, laser treatment, electrostimulation, and thermotherapy, is the backbone of the management of Bell’s palsy [8, 12, 13]. Facial exercises not only hasten recovery during the acute stage but prevent contractures in paralyzed muscles in long term. However, the Cochrane review and other meta-analyses have failed to substantiate tall claims made in many studies. It was concluded that combined physical therapies and steroids plus antiviral drugs may be associated with a better facial function recovery outcome than any single therapy [8, 12].

Kabat rehabilitation, also known as proprioceptive neuromuscular facilitation (PNF), involves the facilitation of the voluntary response of an impaired muscle through the global pattern of an entire muscular section that undergoes resistance [14]. It has shown to be useful to prevent or treat synkinesis. Steroid plus antiviral plus Kabat treatment has shown good facial function recovery [8, 14]. Lately, acupuncture has also been studied as a supplement to other physical therapies. However, these trials are mostly inadequate to draw any conclusions [8, 12, 15]. Hyperbaric oxygen has also been tried to reduce edema over the facial nerve inside the fallopian canal in the temporal bone without any significant clinical recovery [1]. Botulinum toxin can be tried in patients with complications of hemifacial spasm, ipsilateral synkinesis, contralateral hyperkinesis, and facial asymmetry [16].

Most patients with Bell’s palsy have reduced blinking ability and protection of eyes from drying, irritation, and injury merit close consideration. Artificial tears or eye ointments or gels, lubricating eye drops, and eye patches are to be used as per the requirement. In severe cases, tarsorrhaphy can also be considered.

7. Surgery

In the past, decompression surgery during the acute stage was tried to relieve the pressure on the facial nerve inside the fallopian canal [8]. However, it has not met with good clinical recovery, and complications such as injury to the facial nerve and permanent hearing loss outweigh the potential benefits. On rare occasions, facial reanimation surgery may be considered in chronic cases for functional and cosmetic benefits.

It can be concluded patients with Bell’s palsy should be subjected to combination therapy. Steroid plus antiviral plus Kabat treatment, steroid plus antiviral plus electrical stimulation, and acupuncture plus electrical stimulation have shown promising results in patients with Bell’s palsy [8]. However, high-quality trials are needed to recommend any one of them for promising results.