A FUNNY SMILE
History
Oliver is a 7-year-old boy who presents to a paediatric rapid referral clinic with ‘a lopsided face’. His mother noticed that he was drooling from the left side of his mouth for 2 days and his left eyelid has been droopy. When he smiles, his face becomes very asymmetric. He is otherwise well but the drooling has made eating and drinking difficult and a little embarrassing. His left eye also feels dry. The rest of the family are well but you notice that his mother is recovering from a cold sore. There is no history of travel or of any bites. He had an appendicectomy last year and had pyloric stenosis operated on in infancy.
Examination
The child’s mouth droops on the left side. His smile, in particular, is asymmetric. It is well delineated with the normal facial creases on the right side of the face, but on the left side it is poorly formed and weak. He is also unable to shut his left eye. There are no other cranial nerve abnormalities and the neurological system is otherwise normal. Otoscopy is normal and his blood pressure is 107/67 mmHg. There are no other signs.
Questions
• What is the likely diagnosis?
• What is the treatment?
• What is the prognosis?
Medicine
The most likely diagnosis is a left-sided Bell’s palsy. This is a lower motor neurone palsy of the facial nerve. In lower motor neurone palsies, the whole side of the face is weak. Taste on the anterior two-thirds of the tongue on the involved side is lost in about half of cases and there may be facial numbness. In upper motor neurone facial nerve palsies, there is preserved forehead power and eye closure. The facial palsy is said to occur due to oedema of the facial nerve as it crosses the facial canal in the temporal bone. It may occur 2 weeks after a viral infection. Herpes simplex and varicella zoster are said to be causative. Epstein–Barr virus, Lyme disease and mumps have also been implicated. In chronic cases, other causes, such as otitis media, hypertension, tumours (facial nerve or brain stem tumours), leukaemia and trauma, should also be considered. If the facial palsy is thought to be due to an upper motor neurone facial palsy then cranial imaging with a magnetic resonance imaging (MRI) scan should be undertaken. If the child presents within 1 week then steroid treatment with prednisolone 1 mg/kg once daily (up to 60 mg/day) for 7 days is effective. Treatment with other agents such as aciclovir is controversial. Some paediatricians would only administer it if there is a clear history of contact with herpes, as in our case, or varicella. Eye care is important. As it may not be possible for the child to close his eye, treatment with artificial tears such as hypromellose eye drops and taping of the eye at night may be necessary to prevent an exposure keratitis. Most patients recover within a few weeks. Eighty-five per cent make a complete recovery, 10 per cent are left with mild facial weakness and 5 per cent are left with permanent significant facial weakness. Recovery may take up to 6 months.
KEY POINTS
• A lower motor neurone facial palsy affects the forehead and eye as well as the lower part of the face.
• The commonest cause is a Bell’s palsy.
• Treatment with steroids within 1 week of diagnosis is beneficial.
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