What is Bell's palsy?
Bell's palsy is the most common type of peripheral, unilateral, infranuclear and idiopathic paralysis of the facial nerve.
What is the aetiology of Bell's palsy?
1. Age: Bell's palsy can occur at any age
2. Sex: Both sexes are equally affected except females in the third trimester of pregnancy who are at increased risk
3. 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
4. Viral aetiology has been suggested
5. Idiopathic: In a majority of cases, the cause cannot be detected
6. Exposure to cold may trigger the vasospasm
Explains in details about the theory of vasospasm in case of Bell's palsy.
Site of vasospasm: 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 oedema of the nerve. The fibrous tissue and bony facial canal surrounding the facial nerve cause further oedema 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.
What are the clinical features of Bell's palsy?
1. Sudden onset unilateral paralysis
2. Vertigo in early stages
4. Loss of taste sensation
5. Reduced lacrimation
Signs of Bell's palsy seen on the face:
1. No wrinkling of the forehead
2. Angle of mouth deviates to the normal side
3. Inability to blow cheek (Buccinator function)
What are the investigations required for diagnosis of Bell's palsy?
Investigations required for diagnosis of Bell's palsy are:
1. Routine blood and urine tests
2. CT Scan temporal bone
3. X-ray mastoid- Schuller's view
4. Topographic tests are done to assess the function of the accessory branches. They include :
- Lacrimation (Schirmer's test)
- Stapedial reflex
- Salivary flow tests
- Taste from anterior 2/3rd of tongue
5. Test for prognosis:
- Electromyography (EMG)
- Nerve excitability testing (NET)
- Maximal stimulation test
- Electroneurography (ENG)
7. Blood sugar and VDRL test
What is the treatment of Bell's palsy?
Treatment of Bell's palsy is as follows:
A) Medical treatment of Bell's palsy:
The aim of the medical treatment is to establish a good blood supply and reduce the oedema around the facial nerve.
1. Oral steroids: Oral prednisolone can be given, 1mg/kg/body wt in tapering daily divided doses over period of 2-3 weeks
2. Vasodilators help in reducing the vasospasm in the blood vessels
3. Multivitamins, Vitamin B6, B12, B1 and injection methyl cobalamine supplementation
4. Eye care by using eye pads and moistening eye drops
5. Facial physiotherapy:
- Electrical stimulation of the facial nerve at level of stylomastoid foramen prevents degeneration of the muscles
- Facial physiotherapy helps to prevent disuse atrophy of facial muscles
B) Surgical treatment of Bell's palsy:
Facial nerve decompression of the vertical part of the facial nerve is done. However, 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 fibres are seen.
Surgical treatment is indicated when:
1. Electrical evidence of nerve degeneration
2. Incomplete return of facial nerve function within 60 days
3. Recurrent facial paralysis.