Clinical neurophysiology of cranial nerve disorders

Electrophysiologic techniques are available to measure many of the cranial nerves. The procedures can be done using equipment available in standard clinical neurophysiology laboratories. These studies can aid in localization of cranial nerve lesions as well help identify the underlying pathology and possibly aid in prognosis. The trigeminal pathways can be measured using the blink and masseter responses. The facial nerve is measured by the blink response and by direct facial stimulation; techniques such as lateral spread can identify specific abnormalities. The spinal accessory nerve is measured using nerve conduction techniques. Needle examination can be routinely performed on muscles innervated by cranial nerves V, VII, X, XI and XII. These studies reliably measure the functional integrity of cranial nerves and their central pathways. Intraoperative monitoring of the cranial nerves is useful in certain surgeries. This chapter reviews current techniques used to evaluate cranial nerves, emphasizing the methods available in most clinical neurophysiology laboratories.