Introduction to Bell’s palsy
Bell’s palsy is the sudden onset of weakness (paresis) or complete loss of movement (paralysis) of one side of the face. It is very traumatic for patients and should be regarded as a medical emergency. The correct management in the first 14 days is crucial to improve the outcome.
In most cases, the face will recover to normal, but in some cases, it may not recover fully. Early decompression surgery (within 14 days), utilizing the middle cranial fossa approach, may benefit this subset of patients and prevent poor long-term outcomes (1,2). Electrodiagnostic testing is indicated in those patients with complete loss of function. Dr Hofmeyr has experience and has performed numerous middle cranial fossa surgeries for the facial nerve for different indications.
What is Bell’s palsy?
Bell’s palsy is the most common cause of sudden facial palsy. Scottish anatomist Sir Charles Bell first described it in 1821 (3). Bell’s palsy occurs on one side of the face, is sudden in onset and is often preceded by pain behind the ear.
The annual incidence of Bell’s palsy is 15-40 per 100,000 people. There is an equal male-to-female ratio and a three times greater incidence in pregnant females. Familial inheritance has been found in 4-14% of cases, with a recurrence rate of 10-12%. The left and right sides are equally involved, and less than 1% of cases are bilateral. It is also considered to be four to five times more likely to occur in people with diabetes(4,5)
Bell’s palsy is more common in adults than in children. It has a poorer long-term outcome in older patients.
Although still considered by some as an idiopathic disorder (unknown cause), evidence suggests that Bell’s palsy is caused by the herpes simplex virus (cold sore virus).
The facial nerve
Bell’s palsy is a condition or disorder of the facial nerve. The facial nerve is the seventh cranial nerve (CN VII) and is the nerve that travels the longest distance within a bony canal of all the nerves in the human body. The facial nerve controls the muscles of facial expression. Other functions of the facial nerve include taste sensation of the front part of the tongue, some sensation around the ear and the production of tears and saliva.
Facial nerve palsy, paralysis and paresis
The term “palsy” refers to various types of paralysis. A “paralysis “ is the loss of muscle function for one or more muscles, and a “paresis” is a condition typified by a weakness of voluntary movement, partial loss of voluntary movement or impaired movement. In Bell’s palsy, the weakness of the facial muscles is not due to the muscles themselves but to an injury of the facial nerve.
Although the impaired movement of the face is by far the most distressing symptom, it should be realized that the other functions of the nerve are also affected.
From a clinical, prognostic and management viewpoint, it is essential to distinguish between patients with paresis and those with paralysis as the former caries a better prognosis.
Diagnosis of Bell’s palsy
Bell’s palsy is a diagnosis of exclusion that eliminates other reasonable possibilities. It is a clinical diagnosis, and no confirmatory test exists. It is of sudden onset, temporary duration, lack of progression and clinically complete resolution of the inflammation. If a taste disturbance and pain behind the ear are present, it is caused by a virus. Regular meticulous clinical examination in the first 14 days will distinguish between patients with paresis (weakness) and paralysis (complete loss of movement).
It is advisable to use a standardised grading system, such as the House Brackmann or Sunnybrook facial nerve grading system, to record observations (7,8).
Other symptoms
Patients often complain of the following:
- Pain behind the ear
- Taste disturbance (dysgeusia)
- Increased sensitivity to touch (somatophobia)
- Increased sensitivity to loud sounds (hyperacusis)
- Reduced sensation of the cheek and the cornea of the eye
- Dizziness and vertigo
- Increased tearing of the eye
- Reduced tearing and a dry eye (sometimes both sides)
- Choking and irritation on swallowing
Special tests
The following tests may be of use to exclude other conditions and to treat Bell’s palsy:
- Diagnostic hearing tests, including word recognition score
- Immittance and reflex testing of the ear
- Computed tomography (CT scan) of the temporal bone
- Magnetic resonance imaging (MRI) with gadolinium
- Blood tests
- Plain X-rays of the lateral skull base to exclude sclerosteosis
- Electrodiagnostic testing
- Topographic tests
- Auditory brainstem response audiometry (ABR)
- Balance and vestibular testing
Other causes of facial palsy
- Ramsey Hunt syndrome (Herpes zoster oticus)
- Mobius syndrome, congenital lower lip paralysis, Melkersohn Rosenthal syndrome, marble bone disease (e.g. sclerosteosis)
- Birth trauma, temporal bone fractures, facial lacerations, penetrating facial wounds
- Acute otitis media, otitis media with effusion (OME), malignant otitis externa, syphilis, tuberculosis, HIV/AIDS, glandular fever, Lyme disease
- Cholesteatoma, acoustic neuroma/vestibular schwannoma, facial nerve neuroma, haemangioma, haemangioblastoma, meningioma, paraganglioma (glomus tumour), leukemia, parotid tumour, rhabdomyosarcoma.
- Diabetes mellitus, thyroid problems, pregnancy, auto-immune disease
- Multiple sclerosis and Guillain-Barre syndrome
Why perform electrodiagnostic tetsing
Patients with complete paralysis may have different grades of injury to the nerve. The nerve may degenerate in some cases, resulting in a less satisfactory outcome. Recovery may take longer, be incomplete and lead to abnormal function.
Electrodiagnostic testing can help to differentiate patients with intact conduction (better outcome) and those with degeneration (poorer outcome). Nerve stimulation tests using surface electrodes are used. It is recommended that the first stimulation test be done on day three after the onset of the palsy. The maximum stimulation test (MST) and electroneurography (ENOG) are two tests that are performed. It can help monitor nerve damage progression in the first few days (9).
A more accurate prognosis can be given to a patient with the information obtained. It is mandatory for those patients in which decompression surgery is contemplated. Patient participation is good because it is an immense relief when the worried patient feels the muscles contract on stimulation.
Visual observation with electrostimulation
A variation of the ENOG test is to observe the muscle contractions produced simultaneously while measuring the compound action potentials. Additional information is obtained; this test can be called ‘visual ENOG’. This testing method is especially suitable for use with a small nerve stimulator. If the evoked muscle contractions drop to 50% of normal, the patient can be referred for ENOG testing.
Topographic tests for Bell’s palsy
Topographic tests are of historical interest and are not of much clinical use for determining the site of the lesion in Bell’s palsy or predicting the outcome. These include Schirmer’s test for lacrimation, stapedial reflexes, electrogustometry and salivary flow testing ().
Management of Bell’s palsy
Every facial palsy should be regarded as an emergency
After excluding other causes of facial paralysis, treatment of Bell’s palsy is medical at first (10,11). Fortunately, 85% of patients with Bell’s palsy have a full return of facial function.
The referring doctor should start steroid treatment immediately and not delay until a specialist is seen. When requesting an appointment with a specialist, the urgency should be stressed, and the specialist should see the patient within 1-2 days (10).
- Systemic steroids: Prednisone is prescribed initially for five days for both complete and incomplete palsies. Depending on whether it is a weakness (paresis) or total loss of movement (paralysis), the dose and duration of treatment are then adjusted accordingly. Prednisone should never be stopped abruptly because rebound inflammation can lead to further injury to the nerve.
- Antivirals may be of benefit if started within three days of the onset.
- Analgesics: Steroids usually help reduce pain, but additional analgesics may be required.
- Eye care is of significant importance. Because the eye cannot close, natural tears or a tear gel should be prescribed. The eye should also be protected at night.
- Serial electrodiagnostic testing is indicated for all patients with paralysis. Due to limited value, it is not performed before three days after the onset.
- Decompression surgery: The consensus is that, if surgery is performed, the labyrinthine segment of the nerve and meatal foramen should be decompressed via a middle cranial fossa (MCF) approach (1,2)
- Physiotherapy: Most facial nerve researchers do not recommend physiotherapy treatment. The argument that muscle atrophy during total paralysis is prevented does not apply to the facial muscles. Experience gained with patients who needed nerve grafts many months after the onset of the paralysis has shown that excellent movement recurs, even after many months of muscle inactivity, by utilizing physiotherapy.
- Mime therapy is a form of physiotherapy that has shown promising results in limiting long-term complications of Bell’s palsy, such as involuntary simultaneous movement of different facial muscles (synkinesis) and spasms.
- Botulinum toxin injections may help to reduce established synkinesis and asymmetric movements in some patients.
If there is no return of facial movement within four months after the onset of Bell’s palsy, the diagnosis should be reconsidered.
In South Africa, marble bone disease should be excluded in children who present with Bell’s palsy.
Surgery for Bell’s palsy
The aim of early (within 14 days) decompression surgery for Bell’s palsy is to reduce the poor long-term outcome which can occur in some patients (1,2). One predictor of poor long-term outcomes is age. In several studies, it has been shown that in patients older than 60, a poor outcome is to be expected in at least 66%. For younger patients with paralysis, a poor long-term outcome ranges from 10 to 25%.
Poor long-term outcomes may include, to any degree:
- Permanent weakness
- Permanent complete loss of movement
- Involuntary simultaneous movement of different facial muscles (synkinesis)
- Spasms of facial muscles
- Contractures of facial muscles
- Facial asymmetry
- Dry eyes, corneal abrasion and blindness
- Reduced ability to close the mouth
- Impaired taste (dysgeusia)
- Impaired speech (dysarthria)
- Psychological problems
The challenge is identifying the subset of patients with a potentially poor outcome early enough. Regular, meticulous clinical examinations using a grading system such as the House Brackmann facial nerve grading system will help identify patients with paralysis. Electrodiagnostic testing (ENOG) will then quantify the percentage of degeneration compared to the intact side.
In selected patients, surgical decompression of the mental foramen and labyrinthine segment of the facial nerve, utilizing a middle cranial fossa (MCF) approach, has proven to improve the outcome. If performed by appropriately trained surgeons, it is effective, safe, preserve hearing and improves long-term facial motor function in patients.
Left meatal foramen with constriction of facial nerve (white arrow) and decompressed labyrinthine segment (black arrow).Left decompressed facial nerve at meatal foramen (white arrow).
Decompressing the nerve through the mastoid (transmastoid) has been abandoned. It is impractical since the facial nerve’s narrowest and most critical point of compression and conduction block is at the mental foramen and labyrinthine segment.
Dr Hofmeyr's experience
Dr Hofmeyr has experience and has performed over 100 middle cranial fossa surgeries for the facial nerve for different indications. Working with his late mentor, Dr H Hamersma, he gained vital experience performing the middle cranial fossa approach in complex cases and patients with sclerosteosis.