Bell’s palsy is a clinical diagnosis based on symptoms as well as history and physical exam findings (Misulis 2010). The physician may ask the patient to “show me your teeth” (for palsy of lower facial muscles) and “close your eyes” (for assessing upper facial muscles). The timing of onset of symptoms is also important, as Bell’s palsy typically has a sudden onset and progression as opposed to other causes of facial palsy such as tumors, which typically cause a gradual progression of muscle weakness over the course of weeks (Baugh 2013).
Pregnancy, diabetes, and recent influenza or other upper respiratory illnesses are also suggestive (Baugh 2013). Multiple family members with a history of Bell’s palsy may also point to the diagnosis. Notably, certain familial cases of Bell’s palsy may be associated with increased risk of lasting problems with control of the eyelid, dry eye, and “crocodile tears” (Zaidi 2005).
Examination of the ear, mouth, head, neck and skin is also important. Polyps in the ear may be a sign of cholesteatoma, a growth of skin tissue that can compress the facial nerve. Careful examination of the soft palate, tongue, and tonsils can help rule out Ramsay Hunt syndrome (a syndrome linked to varicella zoster virus infection that causes facial paralysis and a characteristic rash) or a parotid tumor (tumor of a salivary gland found in the cheek). Finally, the skin should be carefully examined for signs of Lyme disease (ie, circular, outwardly expanding rash), which can also cause facial palsy (Holland 2004; Mosshammer 2013). Notably, although Bell’s palsy is rare in children younger than 10 years old, up to 50% of reported cases of facial paralysis in this population are attributable to Lyme disease (Zandian 2014).
Additional testing is not typically needed for Bell’s palsy. However, laboratory tests such as a complete blood count (CBC), erythrocyte sedimentation rate (ESR) (Kassner 2012), C-reactive protein (CRP), Lyme titer, electrolytes, blood urea nitrogen (BUN), creatinine, and liver function tests may help if another cause of facial weakness is likely. Imaging studies such as magnetic resonance imaging (MRI) may also help rule out a tumor in the case of a gradual onset of facial weakness/paralysis (Misulis 2010).
Electroneurography can help provide prognostic information for people with complete facial muscle paralysis. Electroneurography uses electricity to stimulate the facial muscle on both sides of the face. The response of the facial muscle evoked by the stimulus is lessened on the side of the face affected by Bell’s palsy, and the degree of nerve degeneration can be quantified by comparing the responses on both sides of the face. People with Bell’s palsy whose muscle response is found to be weakened by ≥90% in the first three weeks are more likely to have long-term facial muscle weakness or trouble with involuntary movements of facial muscles than those with less severe findings (Gilden 2004).
The severity of Bell’s palsy can be graded using different scales. Two commonly used systems are the House-Brackmann Facial Nerve Grading System and the Sunnybrook Facial Grading System (Ng 2013). The House-Brackmann system allows clinicians to classify facial nerve problems into six different categories based on facial muscle strength and function and the appearance of the face at rest. The system also allows clinicians to evaluate the recovery and monitor disease progression and the response to treatment (Reitzen 2009; Yen 2003). The Sunnybrook scale measures facial symmetry at rest and during voluntary movements as well as involuntary muscle movements and scores them on a scale of 0 to 100. Although both systems can be used to help clinicians assess the severity of Bell’s palsy, they may not adequately assess aspects of Bell’s palsy such as facial comfort and problems with tearing that can affect quality of life (Ng 2013).