Introduction
Bell's palsy is an acute-onset peripheral facial neuropathy and is the most common cause of lower motor neuron facial palsy. The affected nerve is the seventh cranial nerve or facial nerve. The facial nerve and the facial muscles develop from the mesoderm of the second branchial arch. Facial muscles are remnants of panniculus carnosus, the subcutaneous muscle of animals.
What Causes Bell's Palsy?
The cause of Bell's palsy is not clear. Bell's palsy is not the result of a stroke or a transient ischemic attack. While stroke and ischemic attacks are capable of causing Bell's palsy, their role in Bell's palsy is not due to either of these conditions.
Most physicians believe, as per literature, that Bell's palsy is because of the facial nerve compression and ischemia that occurs when this cranial nerve is inflamed. The inflammation might be caused due to the narrow facial canal opening at a segment (labyrinthine segment when the facial nerve arises from its origin-the geniculate ganglion). Most cases are thought to be caused by the herpes virus that causes cold sores.
In most cases of Bell's palsy, the nerve that controls muscles on one side of the face is damaged by inflammation or edematous physiologic changes. Reduced lacrimation and salivation secondary to parasympathetic stimulatory effect is possible and hence may also occur with Bell's palsy. Similarly, the extent of facial recovery in these patients and impairment is profound not only due to facial and physical changes but also because of the psychosomatic impact on the quality of life. These patients are also more prone to developing ocular abnormalities and a lack or inability to shed tears (decreased tear output).
What Are the Types of Lower Motor Neuron Facial Palsies?
-
Idiopathic lower motor neuron facial palsy.
-
Facial palsy due to viral infection and bacterial infection.
-
Traumatic facial palsy.
-
Neoplastic facial palsy.
-
Bilateral facial palsy.
-
Facial palsy in children.
Bell's palsy is the most common form of lower motor neuron facial Palsy. Sudden onset of LMN facial palsy is most reported in such cases. No other neurologic abnormalities may be found prior in these patients. The onset of Bell's palsy is acute. A common finding of cases attaining maximum paralysis in 48 hours is reported by physicians. All cases are clinically prominent for 5 days. Facial diplegia seen in LMN facial palsy can also be seen in the following diseases or disorders:
-
Miller Fisher variant Sarcoidosis.
-
Mobius syndrome.
Hence a differential diagnosis is often obtained through MRI or CT scan along with a neurologist review, but sudden weakness that occurs on one side of your face should be checked by a doctor right away to rule out these more serious causes.
What Is the Incidence of Bell's Palsy?
Though the etiology and the pathogenesis of facial palsy are multifactorial in origin and can be due to idiopathic, traumatic, neoplastic/malignant, autoimmune, or even congenital causes, most of the facial nerve palsy cases as per current clinical research indicate that Bell's palsy remains the most common type with 70% incidence. It equally affects men and women, at all ages and at all times of the year. Prevalence rates have been reported more in the following cases:
- Increased occurrence in the elderly and patients with diabetes and hypertension than in the common people.
- Increased incidence in women during the third trimester of pregnancy, two weeks preceding delivery, or in the first two weeks postpartum.
Around 1 in every 60 people encounter the occurrence of at least a single episode of LMN palsy in their lifetime. Bell's palsy is common cranial mononeuropathy that has a slightly higher incidence in mid and later life but certainly occurs across all age ranges. The incidence is higher in pregnancy, following viral infection of the upper respiratory tract, in the immunocompromised patients, and in patients with diabetes mellitus (type 2) and hypertension. Pain behind the ear may precede the paralysis by a day or two. Impairment of taste is present to some degree in all cases, rarely beyond the second week of paralysis. Hyperacusis or distortion of sound in the ipsilateral ear (on the same side as facial palsy) due to paralysis of the stapedius muscle is present.
What Are the Muscles Affected by Facial Nerve Spasm and Paralysis?
Though the below-enlisted muscles are affected in Bell's palsy, the key clinical symptom related to a clear diagnosis is when the weakness is present, more particularly in the forehead region or the forehead musculature. The weakness in the forehead may either be partial or even complete to an extent, but it remains an important diagnostic finding. The following are the muscles and their corresponding action:
-
Frontalis - wrinkling.
-
Corrugator supercilii - frowning, vertical wrinkles of the forehead.
-
Orbicularis oculi - closure of eyes.
-
Orbicularis oris - whistling.
-
Buccinator - puffing the mouth.
-
Dilator of the mouth - showing the teeth.
-
Platysma - forcibly pulling the angle of the mouth downwards and backward.
The muscle and its correlated action are impacted grossly in this LMN palsy and hence remains a cause of physically debilitating expression in the patient.
What Are the Clinical Features of Bell's Palsy?
-
Sudden onset of mild weakness, which progresses to total facial paralysis of one side of the face.
-
Drooping of saliva.
-
Difficulty in making facial expressions like closing eyes and smiling.
-
Facial droop.
-
Pain behind the ear and pain in the jaw on the affected side.
-
Reduced production of saliva and tears.
-
The affected side shows increased sound sensitivity.
How Can We Diagnose Bell's Palsy?
MRI & CT scanning remain the efficient modalities for the diagnosis of Bell's palsy. Other diagnostic tests include the following:
-
Enhancement of the facial nerve on gadolinium-enhanced MRI.
-
Increased lymphocytes and mononuclear cells in CSF.
-
Tensilon test.
-
Shirmer test.
-
ESR.
-
Blood glucose levels.
How Can We Manage Bell's Palsy?
Acyclovir alone is not a beneficial antiviral agent for Bell's palsy. Also, so far, the scientific evidence that surgical decompression of the facial nerve is effective has not been proven yet and in fact may be harmful. Acyclovir 400 mg 5 times a day for ten days is not recommended. The recommended dosage of Valacycloviris 1000 mg/day for 5 to 7 days, which is also not usually preferred.
80% of patients recover within a few weeks, say about 2 to 12 weeks. 10% of cases typically show permanent disfigurement along with oral incontinence as long-term sequelae. 8% recurrence rate is established clinically in this disease.
The best clinical guide to progress is the severity of the palsy during the first few days after presentation. Recovery of taste precedes motor function. If recovery of taste occurs in the first week, it is a good prognostic sign. Protecting the eye during sleep with the help of a patch, massaging the weakened muscles, and using lubricating eye drops aids in facial recovery.
The most common management is through the drug Prednisolone given 60-80 mg/day in divided doses initially for 4-5 days, then tapering it over the next 7-10 days. This treatment decreases the possibility of permanent paralysis from swelling of the facial nerve in the facial canal. It also reduces severe pain. Early recovery of motor function in the first 5-7 days is the most favorable prognosis after this treatment. Recurrence is due to the reactivation of the virus in conditions like pregnancy. The interval between periods is not predictable.
Conclusion:
To conclude, Bell's palsy is not only the common lower motor nerve palsy that is reported but is also an acutely impairing orofacial disease with a psychosomatic impact on the patient. Although Bell's palsy impairs the patient's physical ability considerably, current research and evidence-based medicine are efficacious in treating Bell's palsy. However, proper physiotherapy, timely neurologic help, and preventive measures can dramatically reduce the long-term impact on these cases affected by Bell's palsy.
