What are the signs and symptoms of Bell's palsy?

Signs and Symptoms of Bell's Palsy

Bell's palsy presents with rapid-onset unilateral facial weakness that includes forehead involvement, developing over less than 72 hours, with complete hemifacial paralysis affecting the entire ipsilateral side of the face. 1

Cardinal Motor Features

The hallmark of Bell's palsy is complete unilateral facial weakness involving both upper and lower facial muscles:

• Inability to wrinkle the forehead on the affected side - this distinguishes Bell's palsy from stroke, which spares forehead function due to bilateral cortical innervation 1, 2
• Inability to close the eye completely on the affected side, even with maximal effort, leading to risk of corneal exposure 1
• Inability to raise the eyebrow on the affected side 2
• Drooping of the corner of the mouth with visible asymmetry at rest and decreased or absent nasolabial fold 1
• Inability to smile symmetrically, with the mouth pulling only toward the unaffected side 1
• Drooping of the upper eyelid with incomplete or absent eye closure 1
• Inability to puff out cheeks due to weakness of facial muscles 1

The entire ipsilateral side of the face is affected because the facial nerve (CN VII) innervates all facial muscles on one side after it exits the brainstem 1. This peripheral location of the lesion means all ipsilateral facial muscles lose innervation, producing the characteristic complete hemifacial weakness 1.

Temporal Profile

• Rapid onset within 72 hours is a cardinal diagnostic feature that must be confirmed 1, 3
• Symptoms typically develop over one to three days, with complete unilateral facial paralysis at 24 to 72 hours 3, 4
• Symptoms typically peak in the first week and then gradually resolve over three weeks to three months 5

Associated Sensory and Autonomic Features

Beyond motor weakness, Bell's palsy frequently presents with additional cranial nerve symptoms:

• Ipsilateral ear or facial pain preceding or accompanying the weakness is a common presenting symptom 1
• Taste disturbance or loss from the anterior two-thirds of the tongue due to involvement of the chorda tympani branch carrying special sensory fibers 1, 2
• Hyperacusis (increased sensitivity to sound) indicating involvement of the nerve to stapedius muscle 1, 2
• Dry eye or excessive tearing reflecting parasympathetic dysfunction 1, 2
• Numbness around the ear on the affected side 4

Severity Grading

The House-Brackmann grading system provides standardized assessment 1:

• Grade 1: No visible facial weakness or asymmetry
• Grade 3: Obvious but not disfiguring asymmetry with slight to no forehead movement and obvious asymmetry when attempting to close the eye or move the mouth
• Grade 4: Inability to close the eye completely, even with maximal effort
• Grade 5: Only barely perceptible facial motion with visible asymmetry at rest, drooping of the mouth corner, and incomplete eye closure with only slight lid movement
• Grade 6: Complete loss of facial tone with marked asymmetry and no movement whatsoever

Critical Red Flags (Excluding Bell's Palsy)

The following features indicate alternative diagnoses and exclude Bell's palsy:

• Forehead sparing suggests stroke rather than Bell's palsy, as central facial weakness spares the forehead due to bilateral cortical innervation 1, 2
• Involvement of other cranial nerves (especially CN V, VI, VIII, IX, X, XI, or XII) suggests central pathology or skull base lesion and mandates imaging 1, 2
• Additional neurologic symptoms such as dizziness, dysphagia, diplopia, weakness in extremities, speech difficulties, or altered mental status should raise suspicion for stroke 1, 2
• Bilateral facial palsy is extremely rare in Bell's palsy and should immediately trigger investigation for Guillain-Barré syndrome, Lyme disease, or sarcoidosis 1, 6, 2
• Gradual onset or recurrent episodes of facial weakness require MRI to exclude structural lesions 1, 6

Common Pitfalls to Avoid

• Do not overlook forehead function assessment - the inability to wrinkle the forehead is pathognomonic for peripheral facial nerve lesions like Bell's palsy versus central lesions 1, 2
• Always examine all other cranial nerves, as involvement of multiple cranial nerves excludes Bell's palsy and indicates serious pathology requiring urgent imaging 1
• Do not accept bilateral facial weakness as Bell's palsy - this presentation demands immediate investigation for systemic causes 1, 6, 2
• Recurrent facial paralysis is not idiopathic Bell's palsy and requires identification of an underlying etiology including herpes zoster, sarcoidosis, Lyme disease, or structural lesions 6