Bell palsy is acute facial paralysis or weakness caused by peripheral cranial nerve VII (facial) dysfunction of unknown etiology. This article provides a brief overview of patient-oriented evidence for the primary care of patients with Bell palsy.

Epidemiology

• The estimated incidence of Bell palsy is 20 to 30 cases per 100,000 people per year.^1–4

• All ages can be affected, with the highest incidence in people 15 to 45 years of age.^1–4

• Women and men are equally affected.^1,2

• An equal number of left-sided and right-sided cases are reported.^3,5

• Bell palsy is associated with nerve edema and mechanical compression of cranial nerve VII.⁶ The anatomy of this nerve is illustrated in Figure 1.⁷

• Based on epidemiologic studies, risk factors include diabetes mellitus, hypertension, immunosuppression, influenza A and other upper respiratory illnesses, and pregnancy.^1,2,3,5,8,9

Diagnosis

• Bell palsy should be suspected in patients with acute onset of unilateral facial weakness or paralysis involving the forehead in the absence of other neurologic abnormalities.⁴

• Alternative diagnoses should be considered in patients with bilateral involvement, sparing of the forehead, abnormal extraocular movements, hearing loss, tinnitus, or vertigo. These findings indicate an upper motor neuron lesion or a lesion involving more than just cranial nerve VII¹⁰ (Figure 2⁷).

• Other diagnoses should be considered in patients with gradual onset of symptoms, prolonged course (more than three months without improvement), limb or bulbar weakness, systemic or localized facial skin cancer, signs of infection, or risk of infection.¹¹

• Additional evaluation should be considered in patients with ipsilateral recurrent Bell palsy because this could suggest an underlying tumor.¹²

• The differential diagnosis of Bell palsy includes structural lesions, infection, autoimmune conditions, stroke, and multiple sclerosis (Table 1).⁷

SIGNS AND SYMPTOMS

• Bell palsy presents as mouth droop, flattening of the nasolabial fold, inability to close the eye, and smoothing of the brow on one side of the face.¹³

• Symptoms of Bell palsy are rarely bilateral.¹⁴

• Symptoms typically develop acutely (over one to three days), peak within the first week, and gradually resolve over weeks to months.

• Patients with Bell palsy experience a spectrum of symptom severity. The Sunnybrook scale (https://sunnybrook.ca/uploads/FacialGradingSystem.pdf) and House-Brackmann scale are commonly used to classify symptom severity.

• House-Brackmann scale¹⁵:

  ○ Grade I, normal severity: normal facial function in all areas.

  ○ Grade II, slight severity: slight weakness on close inspection, slight synkinesis, complete eyelid closure with minimal effort.

  ○ Grade III, moderate severity: Obvious but not disfiguring facial asymmetry, synkinesis is noticeable but not severe, may have hemifacial spasm or contracture, complete eyelid closure with effort, mouth is slightly weak with maximal effort.

  ○ Grade IV, moderately severe: Disfiguring facial asymmetry or obvious facial weakness, forehead cannot move, incomplete eyelid closure, mouth is asymmetrical with maximal effort.

  ○ Grade V, severe paralysis: only slight, barely noticeable facial movement, asymmetric facial appearance, forehead cannot move, incomplete eyelid closure, mouth has only slight movement.

  ○ Grade VI, total paralysis: no facial movement.

   

• Physical examination maneuvers to demonstrate the degree and extent of facial weakness include having patients raise their eyebrows, close their eyes, frown, show their teeth, and pucker their lips.

• Patients who can close their eyes tightly and wrinkle their forehead on the affected side should be evaluated for a central lesion.