28 - Facial and Trigeminal Neuropathy

Abstract

Although nerve conduction and electromyography (EMG) studies are used most often to evaluate peripheral nerve and muscle disorders, they can also be used to evaluate lesions of the cranial nerves. Outside of the brainstem, the cranial nerves, other than cranial nerves I (olfactory) and II (optic), are essentially the same as peripheral nerves, carrying motor, sensory, and autonomic fibers. Mononeuropathies affecting cranial nerves VII (facial) and V (trigeminal) are the most common cranial nerve lesions evaluated in the EMG laboratory. The facial nerve can be directly stimulated and recorded using standard nerve conduction techniques. The blink reflex can be used to evaluate both the facial and trigeminal nerves. Facial and masticatory muscles, supplied by cranial nerves VII and V, respectively, can easily be examined with an EMG needle. As in other neuromuscular disorders, the electrophysiologic evaluation of facial and trigeminal neuropathies is used to confirm localization of the lesion, assess the underlying pathophysiology and severity of the lesion, and offer a prognosis. In fact, assessment of severity and prognosis are often the key issues addressed by the electromyographer in the most common cranial neuropathy of all, idiopathic facial palsy (i.e., Bell’s palsy).