Authors: Lewis, Steven L.
Title: Field Guide to the Neurologic Examination, 1st Edition
Copyright ©2004 Lippincott Williams & Wilkins
> Table of Contents > Section 2
– Neurologic Examination > Cranial Nerve Examination > Chapter 22
– Examination of Taste
– Neurologic Examination > Cranial Nerve Examination > Chapter 22
– Examination of Taste
Chapter 22
Examination of Taste
PURPOSE
The main purpose of testing taste is to look for
evidence of dysfunction of the sensory fibers of the facial (seventh)
cranial nerve that convey taste from the anterior tongue.
evidence of dysfunction of the sensory fibers of the facial (seventh)
cranial nerve that convey taste from the anterior tongue.
WHEN TO EXAMINE TASTE
Taste needs only to be tested in patients suspected of
having peripheral (lower motor neuron) facial weakness or in any
patient with a complaint of diminished taste.
having peripheral (lower motor neuron) facial weakness or in any
patient with a complaint of diminished taste.
NEUROANATOMY OF TASTE
Taste from the anterior two-thirds of the tongue is
conveyed by the chorda tympani nerve, which joins the seventh nerve and
sends taste sensation to the medulla.
conveyed by the chorda tympani nerve, which joins the seventh nerve and
sends taste sensation to the medulla.
EQUIPMENT NEEDED TO TEST TASTE
Sugar, water, a paper cup, and a tongue depressor (or a cotton swab).
HOW TO EXAMINE TASTE
-
Prepare the sugar mixture outside the
patient’s view, so that the contents are an unknown. Mix a packet of
sugar with a few drops of water so that it has a paste consistency. -
Explain that you will be testing the
patient’s ability to taste and that it will not be unpleasant. Ask the
patient to close his or her eyes and stick out his or her tongue. -
Using a tongue depressor or a cotton
swab, place some of the paste on one side of the patient’s tongue, and
ask what he or she tastes. Allow the patient to place the tongue inside
the mouth if necessary. Perform the same test on the other side of the
tongue. If he or she appropriately detects “sweet” or “sugar” on both
sides, also ask the patient if the taste is approximately the same on
both sides.
NORMAL FINDINGS
Normally, the patient should be able to taste the sweet
sensation on each side of the tongue, and the taste should be
approximately equal on both sides.
sensation on each side of the tongue, and the taste should be
approximately equal on both sides.
ABNORMAL FINDINGS
-
Diminished or absent taste on one side is
abnormal and suggests a lesion of the facial nerve proximal to where
the chorda tympani joins it; this finding usually also occurs with
other motor signs of a peripheral facial palsy (see Chapter 16, Examination of Facial Strength). -
Absent or significantly diminished taste
on both sides of the tongue is an uncommon finding but would be seen in
patients with a complaint of diminished taste sensation due to a
primary disorder of taste.
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ADDITIONAL POINTS
-
There is no significant role for testing
taste over the posterior tongue, where the taste is carried by the
ninth (glossopharyngeal) nerve. -
Not all peripheral facial palsies are
associated with diminished taste; however, this finding on the side of
a presumed peripheral facial palsy is further evidence for a peripheral
origin for the facial weakness, rather than a central origin.