Acute lower motor neurone facial paralysis is a common presentation in childhood. In most cases, an aetiological agent is not identified and the condition resolves spontaneously. A small number of cases are caused by a variety of underlying pathologies—some of which may have significant morbidity and mortality associated with them.

The facial nerve (VII) leaves the pons at the pontomedullary junction, enters the skull via the internal auditory meatus, and passes along the facial canal. The nerve passes in close proximity to the medial wall of the inner ear and the mastoid cavity. During its course through the petrous temporal bone, branches leave to supply the lacrimal glands, the stapedius muscle in the inner ear, sensation for auricular skin, the sublingual and submandibular salivary glands, and taste fibres to the anterior two thirds of the tongue. The facial nerve exits the skull via the stylomastoid foramen and terminal branches supply the muscles of facial expression.

Bilateral cortical innervation of the muscles of the upper face (orbicularis oculi and frontalis) means that complete facial paralysis is only seen with lower motor neurone lesions. The extent of additional impairment depends on the site of injury. Proximal lesions are associated with impaired lacrimation, hyperacusis, and loss of taste on the anterior two thirds of the tongue.

The pathophysiology of idiopathic facial nerve palsy is uncertain. The condition often occurs two to three weeks following a viral illness. Active viral invasion of the nerve or immune demyelination may be responsible for the underlying neuropathy. It is unclear as to whether physical swelling of the nerve plays a significant pathological role. A variety of specific pathologies can also produce an acute lower motor neurone facial paralysis. Table 1 lists some important examples. Acute facial paralysis may manifest itself as a presenting symptom of one such specific disease, or, as is more common, occur as a complication during the course of a recognised illness.

The term “Bell's palsy” refers to a facial palsy of rapid onset related to a lesion of the nerve within the facial canal.1While the majority of authors use the eponym to describe idiopathic facial palsy alone, this is not universal. Descriptive terms are less open to confusion and tend to focus the mind on potential differential diagnoses.

Controversy exists as to the appropriate investigation of children presenting with acute facial paralysis. A full clinical history should be taken, and a detailed physical examination performed. Children with atypical signs or symptoms require urgent specialist referral (see table 2). Otoscopy is mandatory in all patients presenting with facial paralysis. Where adequate auditory acuity cannot be confirmed an audiogramshould be arranged. Hypertension is a rare but well recognised cause of facial paralysis2; all children must have theirblood pressure checked.

The utility of further investigation, in the absence of additional symptoms or specific findings on physical examination, is debatable.

Radiological imaging is essential if additional neurological abnormalities are identified or if malignancy is suspected. Magnetic resonance imaging is especially helpful in identifying brainstem pathology. High resolution computed tomography scanning is better in the evaluation of the intratemporal portion of the nerve.3 Contrast enhanced magnetic resonance imaging can identify sections of affected nerve in idiopathic facial palsy.4 This expensive and invasive test is not indicated in the majority of children.

Facial paralysis is a recognised feature of leukaemic recurrence in both adults and children. A small number of cases of facial paralysis in children, occurring as a presenting feature of leukaemia, have also been described. As a result, some authorities have recommended the routine performance of a full blood countfor all children presenting with acute lower motor neurone facial paralysis.5 We have identified six reported cases of leukaemia presenting with facial paralysis in children.6-11 In all but one case,7additional symptoms, documented at presentation, would prompt further investigation. Haematological findings are documented in four of the reports.8-11 Although abnormalities of the blood count were present in each case, changes can be subtle and initial haematological findings were discounted or overlooked in three of the four cases.

Neurophysiological studies can help to provide prognostic information and are useful in evaluating lesions that have not resolved at one month. While several tests exist, many require significant cooperation on behalf of the subject. Two of the simpler tests are the measurement of fibrillation potentials (as part of electromyography) and recording of the blink reflex. Fibrillation potentials are detectable in muscles, which have lost their innervation, after approximately three weeks. Their presence implies significant axonal degeneration. Blink reflex tests utilise the polysynaptic nature of this reflex. Unilateral stimuli, transmitted via the trigeminal nerve (V), produce an early ipsilateral facial (VII) motor response, followed by a bilateral late response. A variety of stimuli can be used to elicit the reflex, for example, electrical stimulation of the supraorbital nerve or a puff of air directed onto the cornea. Recordings are made from electrodes placed over both infraorbital ridges. Absence or delay in the late response can be used to assess facial innervation. Neither test can provide useful information in the acute setting, nor can they differentiate the pathological processes responsible. None the less, such tests can provide objective assessment of facial nerve function and reassure parents and children.

The treatment of idiopathic facial palsy is also controversial. The use of steroids early in the course of the disease has been suggested as a way of reducing the duration of paralysis and the risk of long term impairment. A meta-analysis of randomised control trials, performed in adults, seems to support this view.12 A larger portion of patients treated with steroids recovered completely and mean time to recovery was shorter. Treatment appears to be more effective when started within 24 hours of onset.13 The benefits of steroid treatment have yet to be proven in children.14 As the vast majority of children will recover completely, with or without treatment, a very large intervention study would be required to show any significant effect.

Herpes simplex and varicella zoster viruses have been implicated in the pathogenesis of idiopathic facial palsy,15 ,16 and the routine use of antiviral agents has been suggested. A study of adult patients suggests that acyclovir alone is less efficacious than steroid treatment.17 The use of acyclovir in combination with steroids does not improve the outcome of idiopathic facial palsy.18

Ramsay Hunt syndrome (or herpes zoster oticus) is caused by varicella zoster virus reactivation in the geniculate ganglion. Unilateral facial paralysis is accompanied by herpetic vesicles in the external auditory canal or on the soft palate. The prognosis for this condition is not as good as that of idiopathic facial palsy.19 Aggressive treatment with intravenous acyclovir, possibly in combination with steroids, is recommended.

A number of other treatments, aimed at improving outcome in idiopathic facial palsy, have been reported in adults. In an open, randomised trial, patients treated with vitamin B₁₂ , alone or in combination with steroids, recovered faster than those treated with steroids alone.20In a randomised, blind study, patients treated with 100%hyperbaric oxygen recovered faster than those treated with steroids and 7% oxygen at the same pressure. Outcome was also improved in the group receiving the higher oxygen concentration.21

Surgical decompression of the facial nerve canal is no longer considered an effective, or appropriate, treatment for patients with idiopathic facial palsy.

Persistent facial weakness has considerable functional and cosmetic implications. Disfigurement can lead to significant psychosocial morbidity. The small numbers of children falling into this group require expert assessment. Feedback training and exercise programmes have been shown to provide some benefit in adult patients with long standing facial nerve paralysis.22 Surgical techniques, aimed at improving function and cosmesis, include nerve repair, graft, or transposition. Nerve transposition involves attaching the distal end of the affected facial nerve to another afferent cranial nerve trunk, for example, the contralateral facial nerve, or a hypoglossal “jump graft”. This technique must be undertaken within two years of paralysis.23 Muscle transposition, or microneurovascular free muscle transfer, can also be considered.

In summary, patients presenting with acute lower motor neurone facial paralysis require a thorough physical examination. Full neurological examination, otoscopy, and blood pressure measurement are mandatory. In the absence of any abnormal symptoms or signs, further investigation is unnecessary. To date there is no clear evidence that any form of treatment improves outcome of idiopathic facial palsy in children. Ninety five per cent of children will recover full function,24 ,25 most within the first three weeks of the illness. Protection of the cornea, with artificial tears and overnight patching, is normally all that is required. Follow up is advisable. Neurophysiological assessment is helpful in patients with weakness persisting beyond three weeks.