Bell's palsy

Bell's palsy is sudden weakness or paralysis on one side of the face caused by dysfunction of the facial nerve, with no identified cause. It often improves over time, though recovery can be incomplete.

Facial nerve: The seventh cranial nerve, which controls facial expression and carries taste and other sensory signals. Bell's palsy results from dysfunction of this nerve, especially its motor fibers.
Corticosteroid: A class of steroid hormones and synthetic drugs that reduce inflammation and immune activity. Early oral corticosteroid treatment improves the chance of facial nerve recovery.
Stroke: Brain injury caused by interrupted blood supply or bleeding within the brain. Stroke can cause facial weakness, but often has other neurological signs and needs urgent care.
Lagophthalmos: Incomplete closure of the eyelids, often leaving part of the eye exposed. Facial weakness can prevent full eyelid closure and put the cornea at risk.
Lower motor neuron lesion: Damage to a motor neuron or its axon between the brainstem and the muscle it controls. A facial nerve lesion weakens both the upper and lower face on the affected side.
Eye protection: Measures that prevent injury to an eye that cannot close or blink normally. Incomplete eyelid closure can dry and damage the cornea on the weakened side.
Ramsay Hunt syndrome: Facial nerve palsy associated with reactivation of varicella-zoster virus, often with ear pain or blisters. A rash or severe ear pain points toward this identifiable cause rather than Bell's palsy.
Exposure keratopathy: Corneal damage caused by prolonged exposure of the eye surface to air. Reduced blinking and eyelid closure can lead to painful, vision-threatening corneal injury.
Facial nerve nucleus: A group of brainstem neurons that gives rise to motor fibers of the facial nerve. Its location helps distinguish peripheral facial weakness from weakness caused by a brain lesion.
Electroneurography: A test that measures electrical responses in a nerve after stimulation. It can help estimate facial nerve damage in severe cases and inform prognosis.

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