If someone suddenly has one-sided facial weakness, this is usually due to problems within the nervous system that send electrical message to the group of affected facial muscles. It can be either the brain or the facial nerve.
Facial weakness may also cause difficulty in closing eyes, chewing, eating, drinking, talking and may lead to dry eye and dry mouth.
When we see someone who suddenly develop asymmetry face, most of us will straight away think that he/she must be suffering from stroke. However, there are also other reasons such as Bell's palsy, brain tumour etc.
Facial nerve & facial weakness
Bell's palsy is not life-threatening. In Bell's palsy, the facial nerve is swollen but the reason is not clearly known though it is related to some viral infection. As the facial nerve run through a tight space around the skull, it will get compressed and injured when it is swollen. Thus, it loses its function and results in weakness of the muscles it controls.
The severity of facial weakness in Bell's palsy differs from mild to severe. It is most obvious when the sufferer is asked to show his/her teeth. It may take weeks to months to recover its strenght depending on the severity. The sooner it improves, the higher the chance that the sufferer will regain full facial muscle strenght. If the weakness persists for months, then there is higher chance that the weakness may not recover fully.
Another more worrying cause of sudden one-sided facial weakness is stroke. Stroke is either caused by blockage of blood vessel that supply the brain (ischemic stroke - more likely) or bleeding in the brain. In stroke, not only the facial nerve is affected, it often involves other muscle groups in the head and limbs as well. Thus, the stroke sufferer may also have one-sided weakness in his/her arm & leg.
Ischemic stroke
Tumour in the brain or around the facial nerve may compress the nerve and cause facial weakness. As tumour (also bleeding in the brain) will occupy some space in the skull, it will increase the pressure within the skull and produce symptoms such as headache, vomiting, visual disturbance, altered concious level and even coma. This is life threatening and the patient should get immediate medical attention.
Brain tumour in a CT scan
How to differentiate between Bell's palsy, stroke and brain tumour when someone has one-sided facial weakness?
As a rule of thumb:
If the weakness involves other part of the body other than the face, ie limbs, then it is NOT Bell's palsy, but could be stroke or brain tumour.
If no other part of body is involved other than the face, it could be Bell's palsy, brain tumour but UNLIKELY to be stroke.
If there are symptoms of persistent vomiting, visual disturbance and altered mental status, then it is NOT Bell's palsy, but could be stroke or brain tumour. Generally in stroke, the symptoms occur suddenly but for brain tumour, the symptoms develop gradually. Only a brain scan (CT scan) can differentiate both.
If there is only pure one-sided facial weakness and nothing else (except may be some mild headache), then it is LIKELY to be Bell's palsy.
If you are not sure, see your doctor for proper examination.
For Bell's palsy, doctors may prescribe steroids (prednisolone 1mg/kg or 60mg/day) for 6 days, then taper down the dose for 10 days. This has been shown to reduce facial nerve swelling, reduce the duration and increase the chance of full recovery. It is most effective if taken within 3 days of onset of facial weakness. However, those who do not take steroids also have a chance to recover fully.
Anti-viral drugs can be prescribed together with prednisolone but its effectiveness is still not clear. Eye drops and eye patch can be used especially during sleep to relieve dry eyes.
