What are the characteristics of facial droop in Bell's palsy?

Facial Droop in Bell's Palsy: Clinical Characteristics

Primary Clinical Appearance

In Bell's palsy, the facial droop involves complete unilateral weakness of the entire affected side of the face, including the forehead, with visible asymmetry characterized by reduced forehead wrinkling, flattening of the nasolabial fold, drooping of the corner of the mouth, and inability to close the eye on the affected side. 1, 2

Specific Observable Features

Upper Face Involvement

• Forehead paralysis with inability to wrinkle or raise the eyebrow on the affected side, which is the key distinguishing feature from stroke 1, 3
• Drooping of the upper eyelid with incomplete or absent eye closure (lagophthalmos) 4, 2, 5
• Excessive tearing from the affected eye due to impaired lacrimal drainage 5

Mid and Lower Face Involvement

• Complete flattening or absence of the nasolabial fold on the affected side 2, 6
• Drooping of the corner of the mouth with visible asymmetry when at rest 4, 2
• Drooling from the affected side due to oral incompetence 2
• Inability to smile symmetrically, with the mouth pulling only toward the unaffected side 4

Severity Grading of Facial Droop

The House-Brackmann grading system provides a structured assessment of facial droop severity 4:

Grade 1 (Normal)

• No visible facial weakness or asymmetry 4

Grade 2 (Mild Dysfunction)

• Slight weakness noticeable only on close inspection with minimal asymmetry at rest 4
• Near-normal forehead movement and eye closure with minimal effort 4

Grade 3 (Moderate Dysfunction)

• Obvious but not disfiguring asymmetry between the two sides 4
• Slight to no forehead movement with obvious asymmetry when attempting to close the eye or move the mouth 4

Grade 4 (Moderately Severe Dysfunction)

• Obvious weakness with disfiguring asymmetry 4
• No forehead movement and inability to close the eye completely even with maximal effort 4

Grade 5 (Severe Dysfunction)

• Only barely perceptible facial motion 4
• Visible asymmetry at rest with drooping of the mouth corner and decreased or absent nasolabial fold 4
• Incomplete eye closure with only slight lid movement 4

Grade 6 (Total Paralysis)

• Complete loss of facial tone with marked asymmetry and no movement whatsoever 4

Distinguishing Features from Stroke

The critical distinguishing feature is forehead involvement—Bell's palsy affects the entire ipsilateral face including the forehead, while stroke spares forehead function due to bilateral cortical innervation of the upper facial muscles. 1, 3

• In Bell's palsy, the patient cannot wrinkle the forehead or raise the eyebrow on the affected side 1
• In stroke, forehead function remains intact bilaterally while only the lower face shows weakness 1
• Stroke typically presents with additional neurologic symptoms such as limb weakness, speech difficulties, or altered mental status, which are absent in Bell's palsy 1

Anatomical Basis of the Droop Pattern

The facial nerve (CN VII) innervates all ipsilateral facial muscles after exiting the brainstem, so a peripheral lesion in Bell's palsy causes complete hemifacial weakness affecting upper and lower face equally. 1

• The lesion typically occurs within the narrow temporal bone canal where inflammation causes nerve compression 1
• All ipsilateral facial muscles lose innervation, producing the characteristic complete unilateral facial droop 1

Associated Clinical Features

Beyond the visible droop, patients may exhibit 1, 3:

• Taste disturbance on the anterior two-thirds of the tongue due to chorda tympani involvement 1
• Hyperacusis (increased sensitivity to sound) from stapedius muscle paralysis 1, 3
• Dry eye despite excessive tearing, due to impaired tear film distribution 1, 3
• Ipsilateral ear or facial pain as a common presenting symptom 1

Temporal Evolution of the Droop

• Onset occurs rapidly over 24-72 hours, distinguishing it from slowly progressive causes 3, 7
• Symptoms typically peak within the first week after onset 7
• Most patients begin showing recovery within 2-3 weeks, with complete recovery typically occurring within 3-4 months 3

Critical Clinical Pitfall

Failure to test forehead function can lead to misdiagnosis of stroke as Bell's palsy or vice versa—always assess the patient's ability to wrinkle the forehead and raise the eyebrows bilaterally. 3