How is Bell's palsy diagnosed?
Although Bell's palsy is not life-threatening, it shares symptoms in common with serious conditions, such as stroke. Therefore, emergency medical attention is a wise and necessary precaution. Bell's palsy affects the facial nerve, unlike most strokes associated with facial weakness which affect higher nerve centers ultimately supplying the facial nerve.
These two disorders can be distinquished clinically because most strokes do not cause weakness of the forehead or eyelid muscles.
The fact that Bell's palsy is a diagnosis of exclusion becomes apparent in the course of the medical examination--the usual mode of examination is to rule out other disorders until only Bell's palsy is left. Disorders that need to be excluded include demyelinating disease (e.g., multiple sclerosis), stroke, tumors, bacterial or viral infection, and bone fracture.
During the physical examination, the afflicted individual is asked about recent illnesses, accidents, infections, and any other symptoms. A visual exam of the ears, throat, and sinus is done, and hearing is tested. The extent of the symptoms is assessed by grading the symmetry of the face at rest and during voluntary movements, such as wrinkling the forehead, puckering the lips, and closing the affected eye. Involuntary movements are assessed in combination with the voluntary movements. Neurologic exam is done to rule out involvement of other parts of the nervous system except for the facial muscles, which would exclude the diagnosis of Bell's palsy.
In response to the individual's medical history, blood tests and possibly a cerebrospinal fluid (CSF) analysis are ordered. The results of these tests help determine the presence of a bacterial or viral infection or an inflammatory disease. Electrophysiological tests, in which a muscle or nerve is artificially stimulated, may be used to assess the condition of facial muscles and the facial nerve. Common tests include electromyography, which measures voluntary muscle movement, and nerve conduction velocity, which determines the extent of nerve degeneration. Radiological tests may also be included, such as an x ray, as well as imaging tests, such as magnetic resonance imaging (MRI) and computed tomography. These tests--especially MRI--allow an excellent view of the nerve itself.
Once all other possibilities are exhausted, a diagnosis of Bell's palsy is made. The following weeks are a period of watchful waiting. Further examinations are done to track recovery. Results from nerve conduction tests may be used to predict an outcome. However, this use is questioned by some doctors and medical researchers since evidence for their predictive value is inconclusive.
If facial movement, even a small amount, has not returned within 3-4 months, the diagnosis of Bell's palsy may need to be reevaluated.