Cranial Reflexes and Related Techniques

Although a certain level of expertise is necessary, electrophysiologic study of cranial reflexes is not technically demanding, time-consuming, or associated with substantial patient discomfort. The information obtained may document objective abnormality and assist with localization. The blink reflexes are useful for studying the function of the trigeminal and facial nerves and their central connections in the brain stem. When NCS in the limbs suggest a demyelinating peripheral neuropathy, the blink reflex can provide information about involvement of proximal nerve segments. Patterns of involvement of the facial and trigeminal nerves are often helpful in suggesting the type of neuropathy under investigation. The jaw jerk is useful in assessing the mandibular division of the trigeminal nerve, and it can aid in evaluating patients with suspected sensory ganglionopathies. The MIR is sometimes helpful in evaluating patients with demyelinating neuropathies and in assessing central inhibition. The great auricular sensory NCS is a useful method to assess proximal somatic sensory function in the upper cervical dermatomes. The CHEPS technology provides a method to study somatic small fiber sensory pathways from the trigeminal dermatomes to the sensory cortex. Although not discussed in this chapter, needle electrode examination of muscles innervated by the trigeminal and facial cranial nerves are usually performed in combination with cranial nerve reflex studies.