Aetiology:

• Age: Can occur at any age.
• Sex: Both sexes are equally affected except females in the third trimester of pregnancy who are at increased risk.
• Primary vasospasm of the blood vessels of the facial nerve. This leads to oedema of the nerve, causing obstruction to capillary and lymphatic supply to the nerve, with partial or complete loss of function.
• Viral aetiology has been suggested.
• Idiopathic: In a majority of cases the cause cannot be detected.
• Exposure to cold may trigger the vasospasm.

Site:

Just as the nerve leaves the stylomastoid foramen, it is surrounded by fibrous tissue. This seems to be the point of constriction in Bell’s palsy.

Pathology:

Vasospasm of the blood vessels of the facial nerve causes edema of the nerve. The fibrous tissue and bony facial canal surrounding the facial nerve cause further edema and compression of the nerve. The above theory is most commonly accepted because during facial nerve decompression, the nerve bulges or herniates out when the facial sheath is slit open. This bulging occurs proximal to the site of palsy, not distal to it.

Clinical features :

• Sudden onset unilateral paralysis.
• Vertigo in early stages.
• Hyperacusis.
• Loss of taste sensation.
• Reduced lacrimation.

Signs of Bell’s palsy seen on the face:

• No wrinkling of the forehead.
• Angle of mouth deviates to the normal side.
• Inability to blow cheeks (Buccinators function).
• Droopy eyelid.

Treatment

A. Medical:

• Oral steroids: Oral prednisolone can be given, 1mg/kg/body weight in tapering daily divided doses over period of 2-3 weeks.
• Vasodilators help in reducing the vasospasm in the blood vessels.
• Multivitamins, Vitamin B6, B12, B1 and injection methylcobalamine supplementation.
• Eye care by using eye pads and moistening eye drops.
• Facial physiotherapy:
  • a)Electrical stimulation of the facial nerve at level of stylomastoid foramen prevents degeneration of the muscles.
  • b)Facial physiotherapy helps to prevent disuse atrophy of facial muscles.

B. Surgical treatment: Facial nerve decompression of the vertical part of the facial nerve has been advocated by many surgeons. Extended decompression from the stylomastoid foramen to internal auditory meatus can be done. During this surgery, the nerve is decompressed from the bony canal and the facial nerve sheath slit open till the facial nerve fibers are seen. However, it must be noted that the surgical treatment for bells palsy is not widely accepted in many countries and is controversial.