Bell's palsy is defined as a unilateral facial nerve (7th cranial nerve) paralysis which leads to the inability to control facial muscles on the affected side. The disease is idiopathic and self limiting with acute onset. There are so many conditions that can cause facial paralysis such as brain tumour, stroke and Lyme disease etc. If no specific cause is identified, then the condition is known as Bell's palsy.
Aetiology of Bell's palsy :
• Bell's palsy is a condition that occurs in both sexes equally at any age.
• The aetiology of disease is not known i.e. idiopathic.
• It is believed to be an inflammatory lesion of the stylomastoid canal, the paralysis being due to compression of the nerve fibres by oedema.
• A cold draught blowing on the ear may be a precipitating factor of the disease.
• Sub clinical infection (persistent or latent infection) of some viruses of Herpes family such as Varicella-zoster and Epstein-Bar viruses may be present.
• Reactivation of a dormant viral infection may be suggested as cause of acute Bell's palsy.
• It has been observed that new activation of virus infection may be preceded by:
-metabolic or emotional disorders
-environmental stress (e.g. cold)
-physical stress (trauma)
In short, above different conditions may trigger the reactivation of facial palsy.
Clinical manifestations of Bell's palsy :
• Onset of disease is acute.
• Paresis may be partial or complete.
• Facial nerve paralysis is mostly unilateral but in extreme rare cases, the palsy may be bilateral causing total facial paralysis.
• There may first be a slight aching pain behind the ear for one or two days then unilateral facial paralysis rapidly develops.
• The eye on the affected side cannot be closed and may be watery. The eye must be protected from drying up, or the cornea may be permanently damaged leading to impaired vision.
• Mouth is drawn over to the opposite side.
• Saliva or fluids may run from the angle of the mouth.
• During chewing, food may collect between the teeth and the paralysed cheek.
• Patient often complains that the affected side feels num, but there is no objective loss of sensation of the skin.
On Clinical Examination (Signs):
• There is paralysis of the upper as well as the lower part of affected side of the face.
• Lines of expression are flattened out on the weak side.
• Patient is unable to wrinkle his brow.
• Also patient is unable to whistle or retract the angle of his mouth.
• He cannot close the eye and on attempting to do so the eyeball rolls up. Eye must be protected from drying up, or the cornea may be permanently damaged leading to impaired vision.
• The nerve to the stepedius muscle and the chorda tympani respectively leave and join the main trunk before it leaves the stylomastoid foramen so signs of affection of these two nerves are absent in most cases of Bell's palsy.
• Because both the nerves to stapedius and the chorda tympani nerve (taste nerve) are branches of the facial nerve, patients with Bell's palsy may compl-ain that sounds seem too loud (hyperacusis) or loss of taste sensation in the anterior 2/3rd of the tongue.
• In some cases artificial denture wearers feel some discomfort.
• Although Bell's palsy is mono-neuritis (one nerve involvement), patients may have ' myriad neurological symptoms' which including-
1. Facial tingling
2. moderate to severe headache/ neck pain
3. Memory problems
4. Balance problems
5. Ipsilateral limb paresthesias
6. Ipsilateral limb weakness and
7. A sense of clumsiness that are unexplained by facial nerve dysfunction.
Pathology of Bell's palsy :
• Pathology of Bell's palsy is thought to be as a result of inflammation of the facial nerve (7th cranial nerve).
• Pressure is produced on the facial nerve where it leaves the skull within its bony canal damaging the nerve or blocking the nerve signals.
• Patients with facial palsy having underlying cause are not considered to be the Bell's palsy.
• Possible causes of facial palsy are Brain tumour, meningitis, stroke, diabetes mellitus, head injury, and inflammatory disease of cranial nerves such as Sarcoidosis, Brucellosis etc.
• In some cases bilateral facial palsy may occur.
• Herpes Zoster of the geniculate ganglion is a rare cause of facial palsy which is accompanied by vesicular eruptions on the anterior 2/3rd of the tongue or in the ear.
Diagnosis of Bell's palsy :
Since the aetiology of Bell's palsy is not known, its diagnosis is based on exclusions by eliminating other possibilities of facial palsy.
Treatment of Bell's palsy :
• Bell's palsy affects each individual in different manners.
• When facial palsy is incomplete, the prognosis for recovery is too good and no treatment is required.
• It is usually sufficient to give aspirin if the ear is painful and to protect the ear from cold.
• Corticosteroids such as prednisolone significantly improve recovery and are thus recommended. It reduces inflammation and oedema during the first week.
• To reduce the pain, heat can be applied to the affected side of the face.
• A splint may be fitted to prevent over stretching of angle of the mouth.
• When voluntary movement begins to return, active facial exercises in front of a mirror should be practised several times a day.
• Surgical decompression is not widely used.
• Electrical stimulation does not hasten recovery and may lead to secondary co-ntractures.
• When recovery does not occur, a nerve anastomosis or a plastic surgery should be considered.
• Antivirus drugs are ineffective in improving recovery from Bell's palsy. They were recommended due to a theoretical link between herpes simplex and varicella zoster virus.
• Complementary therapy like acupuncture efficacy is not known.
• Physiotherapy in beneficial in some cases of Bell's palsy because it improves muscle tone of affected facial muscles & stimulate the facial nerve.
• To prevent permanent contractures of the paralysed facial muscles it is impor-tant to implement muscle re-educational exercises and soft tissues techniques.
• Muscle re-educational exercises are useful in restoring the normal movement of affected muscles.
• In patients with unresolved facial nerve paralysis, transcutaneous electrical stimulation may be an effective treatment.
Prognosis of Bell's palsy :
• Recovery usually starts in three to four weeks and is complete in three to six months but it is sometimes delayed or incomplete.
• Unfortunately it is difficult to recognise cases with poor prognosis at a time when surgical treatment might be considered.
• Recovery is possible when any voluntary contraction of any paralysed muscle can be seen within a month and positive normal intensity-duration curve on electrical stimulation after the first week is strong evidence that the nerve has not degenerated.
• Recovery is not possible if the intensity-duration curve is of the denervation type.
• Regeneration of the nerve is possible but the cosmetic result may be marred (destroyed) by the presence of inappropriate movements such as closure of the eye when it is intended to move the lips, due to random regeneration of fibres to the wrong muscles.
• Spontaneous facial spasm may occur as a rare sequel.
• Recurrence of facial palsy on either side is exceptional but some individuals appear to be unduly susceptible.
History of Bell's palsy :
Bell's palsy was first described by Scottish surgeon Charles Bell in the year 1829.