Signs and Symptoms
The classic sign of Bell’s palsy is unilateral facial paralysis that typically occurs over a matter of hours to a few days (Ferri 2014; Ronthal 2013a). The paralysis may be partial (one-third of cases) or total (two-thirds of cases) and affects both the upper and lower facial muscles (Misulis 2010; Ferri 2014). Sometimes both sides of the face may be affected simultaneously, but this is rare; one study found that bilateral simultaneous facial palsy occurred in less than 1% of cases (Kim 2008).
Typically, the facial weakness worsens during the first few days but usually improves thereafter (Holland 2004; Misulis 2010). The forehead will stop furrowing and the corner of the mouth will droop on the affected side. Another feature of Bell’s palsy is an inability to close the eye as a result of the lower eyelid drooping. Attempting to close the eye can cause the eyeball to roll upward, known as Bell’s phenomenon (Tiemstra 2007). Frowning and pursing of the lips are also impaired by Bell’s palsy (Misulis 2010).
Some individuals with Bell’s palsy describe a feeling of numbness in their face, although facial sensation is left intact (Misulis 2010). Bell’s palsy can impair the formation of tears (lacrimation) as well, resulting in dryness of the eye. However, because Bell’s palsy also impairs control of the eyelids, tears may spill out of the affected eye giving the appearance of over-tearing (Tiemstra 2007; Misulis 2010). In some cases, parts of the facial nerve that supply the tongue and ear can be affected, resulting in loss of taste on the frontal two-thirds of the tongue or intensification of loud noises, also known as hyperacusis (Misulis 2010).
In most cases, the symptoms of Bell’s palsy will resolve completely. However, Bell’s palsy can cause some long-term complications. In some people, the facial nerve will not recover completely, resulting in lasting facial muscle weakness or partial paralysis (Mayo Clinic 2012a). Generally speaking, the more severe the muscle weakness/paralysis, the greater the likelihood for long-term muscle weakness. People who do not have some recovery within 21 days have a greater risk of having lasting facial muscle weakness (Ronthal 2013b).
If the facial nerve does not recover properly, some new nerve fibers may develop disorganized or misdirected connections. This can cause some facial muscles to involuntarily contract along with other muscles, a phenomenon known as synkinesis (Mayo Clinic 2012b). In addition, eye dryness and an inability to close the eyes completely can cause the cornea to become scratched, resulting in lasting problems with vision (Mayo Clinic 2012b).
Differentiating Bell’s Palsy From Stroke
Both Bell’s palsy and a stroke can cause paralysis of one side of the face. However, Bell’s palsy and stroke can usually be differentiated by the presence of other symptoms (Fahimi 2013).
By definition, Bell’s palsy only affects the facial nerve, so the symptoms will be limited to facial muscle paralysis/weakness, decreased tear formation, and problems with taste. Although a stroke can cause similar symptoms, a stroke may also cause other symptoms, such as problems speaking or slurred speech, trouble understanding others, paralysis of the arm or leg on the same side of the body as the facial paralysis, vision problems, and headache (Mayo Clinic 2014).
A physical exam can help distinguish Bell’s palsy (a problem with the peripheral nerves) from a stroke (a problem with the central nervous system), which, unlike Bell’s palsy, will typically cause problems with the muscles of the lower face only (Holland 2004; Misulis 2010; Kölln 2011). As a result, a stroke will typically not cause weakness of the eyelid and forehead, whereas Bell’s palsy can cause impairment of these regions of the face. Generally, when paralysis is caused by a stroke, additional muscles on the same side of the body are usually involved (A.D.A.M. 2013).
Fortunately, emergency room physicians are generally very good at differentiating stroke from Bell’s palsy. Medical attention should be sought when symptoms of facial paralysis begin to appear irrespective of whether they are thought to be caused by Bell's palsy or stroke (Fahimi 2013).