Bell's Palsy

🔍 When to Suspect

Sudden onset of unilateral facial weakness or paralysis, often after a recent viral infection, with no other neurological signs

From the full topic in The Ocean Library: Bell's Palsy

🧭 When to suspect

Bell's palsy is an acute, unilateral, lower motor neurone (LMN) weakness or paralysis of the face of unknown cause, thought to follow inflammation and oedema of the facial nerve (cranial nerve VII) – often viral. It is a diagnosis of exclusion: suspect it when facial weakness develops rapidly, typically reaching its peak within 72 hours, and there is no evidence of another cause such as stroke, Ramsay Hunt syndrome, middle ear disease, or a parotid mass.

The single most important distinction is lower versus upper motor neurone. In Bell's palsy the whole side of the face is weak, including the forehead, because the forehead receives cortical input from both hemispheres while the lower face does not. A stroke therefore spares the forehead. Forehead sparing points away from Bell's palsy and towards a central cause.

Feature	LMN – Bell's palsy	UMN – central cause (e.g. stroke)
Forehead	Weak – cannot wrinkle the brow or raise the eyebrow	Spared – brow wrinkling preserved
Distribution	All of one side of the face	Lower face; forehead relatively spared
Associated signs	Isolated VII; ± altered taste, hyperacusis, post-auricular pain	Limb weakness, dysarthria/dysphasia, other cranial nerves

Supportive features include post-auricular pain, altered taste (dysgeusia), reduced tear production with a dry or watering eye, and hyperacusis on the affected side. Around 7 in 10 people recover completely without any treatment, and early corticosteroids increase the chance of full recovery. The two clinical priorities are to exclude dangerous mimics and to protect the eye.

Source: NICE NG127

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