From the Guidelines
No, true Bell's palsy cannot spare the forehead, as it is characterized by complete facial nerve paralysis on one side, affecting all branches of the facial nerve, including those that innervate the forehead muscles. According to the House-Brackmann facial nerve grading system, as outlined in the clinical practice guideline for Bell's palsy 1, the grading system assesses the degree of facial nerve dysfunction, with Grade 1 indicating normal facial function and Grade 6 indicating total paralysis. Notably, the guideline describes the characteristics of each grade, including the presence or absence of forehead movement. If the forehead is spared during facial weakness, this suggests a central nervous system lesion, such as a stroke, rather than Bell's palsy. The unique pattern of cortical innervation to facial muscles, where forehead muscles receive bilateral cortical input, while the lower face receives only contralateral input, is the basis for this distinction. Key characteristics of Bell's palsy and central lesions include:
- Bilateral cortical input to forehead muscles
- Contralateral input to lower face muscles
- Preservation of forehead innervation from the unaffected hemisphere in central lesions. This distinction is critical for diagnostic purposes, as it helps differentiate peripheral facial nerve disorders like Bell's palsy from central causes of facial weakness, and should prompt immediate medical evaluation, as it may indicate a stroke requiring urgent treatment, as described in the clinical practice guideline for Bell's palsy 1.
From the Research
Definition and Diagnosis of Bell's Palsy
- Bell's palsy is characterized by an acute onset of unilateral, lower motor neuron weakness of the facial nerve in the absence of an identifiable cause 2.
- It usually presents with unilateral facial weakness, reduced forehead wrinkling, nasolabial fold flattening, drooping of the corner of the mouth, and drooling 3.
- The diagnosis of Bell's palsy is based on exclusion, and a thorough history and physical examination are essential for establishing the correct diagnosis 2.
Presentation and Variations
- Bell's palsy typically involves the entire face, including the forehead 4, 3.
- However, there is no clear evidence to suggest that a partial Bell's palsy with sparing of the forehead is a recognized variant of the condition.
- The studies reviewed focus on the typical presentation of Bell's palsy, which involves the entire face, and do not provide information on partial presentations with sparing of specific areas, such as the forehead.
Treatment and Management
- Corticosteroids are the mainstay of treatment for Bell's palsy and should be initiated within 72 hours of symptom onset 2, 5.
- Antiviral therapy in combination with corticosteroid therapy may confer a small benefit and may be offered on the basis of shared decision making 2, 6.
- The effectiveness of additional treatment with an antiviral agent is uncertain, and the current evidence suggests that corticosteroids alone are probably more effective than antivirals alone 6.