Most common cause - idiopathic bell’s nerve palsy

Causes

The differential diagnosis can be divided into four groups: central nerve, peripheral neuromuscular and muscular.

Central nerve weakness is distinguished primarily on the basis of forehead sparing weakness (the upper part of the face is bilaterally represented cortically.

Other causes of peripheral nerve disease include:

• Physical lesions of the cerebellopontine angle (including the classical acoustic neuroma)
• Basal meningitis (which is often bilateral and may be infective or inflammatory, including Lyme disease and sarcoidosis).
• Ramsay Hunt syndrome (herpes zoster of the facial nerve)
• Trauma
• Diseases of the middle/inner ear
• Mononeuritis multiplex

Neuromuscular and muscular mimics are usually easy to distinguish as they are often bilateral, and associated with weakness elsewhere.