Context

The image shows a case of right-sided facial nerve palsy. (Reproduced with permission from CDC)

Isolated facial muscle weakness is an uncommon presentation to the emergency department (ED) and may be quickly diagnosed by the unwary as Bell’s palsy.

The emergency clinician must be aware of two potential pitfalls when presented with a patient with facial weakness:

• Central (UMN) facial weakness must be differentiated from a peripheral (LMN) palsy
• A diagnosis of Bells’ palsy should only be made after the exclusion of other causes of a peripheral facial muscle weakness

Definition

Bell’s palsy is defined as an acute idiopathic peripheral (LMN) facial nerve paresis’ and is the most common cause of acute peripheral facial weakness [1].

To be able to diagnose Bell’s Palsy, there must not be other neurological deficit in the limbs or cerebellar signs, no parotid or neck masses must be present and there must not be any vesicles in the ear, nose or mouth present. Other differentials should always be considered e.g. Lyme’s disease, middle ear infection.

In the UK it has an incidence of approximately 20 cases per 100 000 person years [2], in other words around 50 cases per year will occur in an average ED catchment area.