How is cranial nerve function assessed in electrodiagnostic medicine?

Updated: Aug 06, 2019
  • Author: Brian M Kelly, DO; Chief Editor: Stephen Kishner, MD, MHA  more...
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Answer

Answer

Cranial nerve function also needs to be assessed when symptoms suggest their involvement, as well as when generalized symptoms occur (because cranial involvement also is common in polyneuropathy). Specific tests include the following:

  • Reflexes - Many of these reflex tests were covered in the motor examination section; however, remember these reflex pathways have a sensory afferent pathway and a motor efferent pathway. A lesion of either one impairs the reflex.

  • Blink reflex - This reflex specifically evaluates cranial nerve V (ie, sensory pathway of the trigeminal nerve) and cranial nerve VII (ie, motor pathway of the facial nerve).

  • Gag reflex - This reflex can evaluate either cranial nerve IX (glossopharyngeal) or X (vagus).

  • Romberg sign - This test is often performed but is frequently misinterpreted. Patients are asked to stand with their feet together and then to close their eyes. Loss of balance or excessive sway after the eyes are closed is considered a positive Romberg sign. Mild swaying without loss of balance is normal. If the patient cannot maintain balance with his/her eyes open, the test cannot be completed. A positive Romberg sign implies loss of position sense or severely reduced peripheral sensation in general; however, it does not suggest a cerebellar lesion, which would result in the patient having difficulty maintaining balance with the eyes open or closed.


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