Diagnosis of Bell's Palsy
A diagnosis of Bell's palsy is often based on symptoms and by ruling out other disorders. Other conditions that may cause facial paralysis include facial tumors, certain cancers, and autoimmune diseases. The physician can usually exclude other disorders by taking the patient's history of symptoms, and by examining the head, neck, ears, and eyes.
During the physical examination, the doctor observes the patient's range of movement in different parts of the face (e.g., raising and lowering the eyebrows, closing both eyes). If one eyebrow cannot be raised or can only be lifted slightly, it suggests that one side of the face is weaker. Similarly, if one eye cannot be closed tightly, it indicates a problem with the controlling muscles. If paralysis or muscle weakness is noted in another part of the body, Bell's palsy may be ruled out through diagnostic testing.
Imaging tests such as computerized tomography (CT scan) or magnetic resonance imaging (MRI scan) are used to detect infection, tumor, bone fracture, or other abnormality in and around the facial nerve.
Hearing and balance tests are used to determine if the nerve responsible for hearing is also damaged and assess injury to the inner ear. Tests can be performed to evaluate the eye's ability to produce tears. The sense of taste also can be evaluated to determine the location and severity of a facial nerve lesion.
Electromyography (EMG) assesses injury by electrically stimulating the facial nerve. Electrical current is applied to the skin over the nerve and nerve function is determined by the amount of current needed to cause contraction of the facial muscles. The test is often repeated to assess disease progression and the extent of injury.
Laboratory tests can help the physician determine the underlying cause. For example, a blood test for Lyme disease may be ordered if there is a chance that the patient was bitten by a deer tick, or a blood glucose test may be obtained to determine if the patient has undiagnosed diabetes.