Fast Five Quiz: Bell Palsy Essentials

Helmi L. Lutsep, MD


February 06, 2019

According to the American Academy of Otolaryngology-Head and Neck Surgery Foundation, clinicians should not obtain routine laboratory testing or perform diagnostic imaging in patients with new-onset Bell palsy. At-risk patients who would benefit from specific testing, such as those with suspected Lyme disease, can usually be identified based on history.

Nerve conduction velocities and EMG produce a graphic readout of the electrical currents, displayed by stimulating the facial nerve and recording the excitability of the facial muscles it supplies. These tests may aid in assessing the outcome of a patient who has persistent and severe Bell palsy. This testing is not part of the acute workup; the tests are most useful when performed 3 to 10 days after the onset of paralysis. Note that most electromyographic/nerve conduction studies do not show an abnormality for 3 weeks after a peripheral nerve injury.

Electroneurography is a physiologic test that uses EMG to objectively measure the difference between potentials generated by the facial musculature on both sides of the face in response to a supramaximal electrical stimulation of the facial nerve. Because all electrodiagnostic testing is performed on the nerve distal to the proposed site of injury, sufficient time is needed for wallerian degeneration to occur, usually 48 to 72 hours. Testing should begin 3 days from the onset of complete paralysis.

The nerve excitability test determines the threshold of the electrical stimulus needed to produce visible muscle twitching. This test is technically challenging and has very limited clinical availability.

Read more information about the workup of Bell palsy.


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