Does Bell's palsy spare the forehead?

Bell's Palsy Does NOT Spare the Forehead

Bell's palsy affects the entire facial nerve including the forehead, which distinguishes it from central causes of facial weakness where forehead sparing is typically observed. 1

Key Diagnostic Features of Bell's Palsy

• Bell's palsy is an acute unilateral facial nerve paresis or paralysis with onset in less than 72 hours without an identifiable cause 2, 1
• Bell's palsy involves the entire facial nerve distribution including the forehead, which is a critical distinguishing feature from central causes of facial weakness 1, 3
• The condition leads to partial or complete inability to voluntarily move facial muscles on the affected side of the face 2
• Symptoms typically develop rapidly over 24-72 hours 1

Clinical Examination Findings

• Patients present with unilateral facial weakness or paralysis affecting all facial muscles on one side, including:
  • Inability to raise eyebrows/wrinkle forehead on affected side 1, 4
  • Incomplete eye closure (lagophthalmos) 1
  • Drooping of the corner of the mouth 2, 1
  • Flattening of the nasolabial fold 1
• Associated symptoms may include:
  • Ipsilateral pain around the ear or face 2, 1
  • Hyperacusis (increased sensitivity to sound) 1
  • Taste disturbance on the anterior two-thirds of the tongue 1
  • Dry eye and mouth due to autonomic fiber involvement 1

Differentiating Bell's Palsy from Central Causes

• In central lesions (e.g., stroke affecting the facial motor cortex or corticobulbar tract):
  • Forehead is typically spared due to bilateral cortical innervation of upper facial muscles 1
  • Lower face shows weakness while forehead movement remains intact 1, 3
• In Bell's palsy (peripheral lesion):
  • Complete facial weakness including the forehead 1, 4
  • Inability to raise eyebrows or wrinkle forehead on affected side 1
  • This is a critical examination finding that helps distinguish Bell's palsy from a central cause 1

Assessment Approach

• A systematic assessment of all facial movements should include:
  • Raising eyebrows (tests forehead involvement) 1
  • Closing eyes tightly (tests orbicularis oculi) 1
  • Smiling and showing teeth (tests lower face) 1
  • Puffing out cheeks 1
• The House-Brackmann facial nerve grading system is commonly used to assess severity, with grades ranging from 1 (normal) to 6 (total paralysis) 2, 1

Common Pitfalls in Diagnosis

• Failing to test forehead function can lead to misdiagnosis, as it is critical to distinguish Bell's palsy from central causes of facial weakness 1
• Missing subtle weakness or inadequate eye assessment can lead to missed diagnoses 1
• Bilateral facial weakness is rare in Bell's palsy and suggests an alternative diagnosis 1
• Not recognizing that Bell's palsy is a diagnosis of exclusion after ruling out other causes of facial weakness 2, 1

Remember that proper identification of forehead involvement is essential for accurate diagnosis of Bell's palsy and distinguishing it from central nervous system pathology that would require different management and urgent intervention.