Bell's palsy remains a diagnosis of exclusion and must be distinguished from other causes of facial palsy - see facial palsy for more information
the differential diagnosis includes:
nuclear (peripheral) causes (1)
Lyme disease
this is more likely if the facial weakness is bilateral
history of tick exposure, and arthralgias
look for a rash
Otitis media
suppurative otitis is excluded by examining the ear
there is gradual onset ear pain, fever, and conductive hearing loss
Ramsay Hunt syndrome
herpes zoster may produce an acute facial weakness but is accompanied by a rash within the auricle - geniculate herpes - or on the palate, pharynx, face, neck or trunk. There may be a pronounced prodrome of pain. 2-23% of people with Bell's palsy actually have Ramsay Hunt syndrome and it should be suspected when pain is significant, especially in those aged over 60. (2)
sarcoidosis
sarcoidosis affecting the parotid gland is suggested by recurrent facial palsy
facial weakness is often bilateral
Guillain-Barré syndrome
facial weakness is often bilateral
HIV infection
more likely if the facial weakness is bilateral
look for lymphadenopathy
tumours
cholesteatoma, parotid gland tumours
supranuclear (central) causes (1)
multiple sclerosis
multiple sclerosis should be considered if the palsy is unilateral, in a young adult, is painless, and resolves in 2-3 weeks
stroke
tumours
metastases or primary brain tumours
history of cancer
look for mental status changes
Horner's syndrome and 3rd nerve palsies produce a ptosis
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