A thorough neurologic assessment involves an evaluation of the sensory system. This begins with primary methods such as light touch, pain and temperature, vibration, and joint position.  These tests check if the afferent sensory pathways are intact and if needed, are often followed by discriminative sensory function tests such as stereognosis, graphesthesia, point localization, two-point discrimination, and extinction. These assess the patient’s ability to interpret sensory input. What are discriminatory sensations and how do you assess them?

What do Discriminative Sensations Test?

Discriminative sensations test the patient’s ability to associate, evaluate, and decipher sensations, all functions of the sensory cortex. Before you can assess discriminative sensations, the patient’s sense of touch and position must be intact. Let’s quickly review touch and position sense first.

First, Assess Touch and Joint Position Sense

• To test a patient’s sense of touch, have them close their eyes, then lightly touch the skin (without pressure) with a wisp of cotton, left hand, right hand, and then both simultaneously. Ask the patient to tell you when they feel something and compare one area with another. Document any areas where the patient experiences anesthesia (no sensation), hypesthesia (decreased sensitivity to touch), or hyperesthesia (increased sensitivity).

• Joint position sense or proprioception can be tested with the patient’s fingers and toes. For example, hold the tip of the patient’s thumb and move it slightly upward and downward telling the patient the directions. Then ask the patient to close their eyes and have them identify the direction of the movement of the thumb position. Repeat this several times. Patients can normally identify movements of a few degrees or less (Gelb, 2022). If the patient cannot tell you the correct position of the thumb, try different fingers. Then move to the wrist and repeat the test while flexing the hand up and down. If abnormalities are found, continue to more proximal joints (elbows, shoulders) in the same limb until a joint is found where position sense is intact. Test both upper arms and then move to the lower limbs, beginning with the big toes and advancing to ankles and knees as needed.

If touch and position sense are normal, you can then test for discriminative sensation.
 

Tests for Discriminative Sensation

Reduced or absent discriminative sensation may be a sign of a lesion in the sensory cortex (Bickley et al., 2021). Perform the following tests with the patient’s eyes closed.

• Stereognosis is the ability to identify an object by touching and feeling it. With the patient’s eyes closed, place a familiar object (i.e., paper clip, key, pencil) in the patient’s hand and ask the patient what it is. The patient should be able to correctly identify the object within 5 seconds. Begin with stereognosis, and if abnormalities are found, move on to other methods listed below.

 

• Graphesthesia, or number identification, should be performed if the patient is unable to maneuver an object in their hand well enough to identify it. With the blunt end of a pen or pencil, draw a large number in the patient’s palm. An inability to recognize numbers indicates a lesion in the sensory cortex.

 
 

• Using point localization, briefly touch a point on the patient’s skin with the patient’s eyes closed. Have the patient open both eyes and point to the place where they were touched. The patient should be able to perform this accurately.

 

• Perform extinction by touching each arm individually, then simultaneously touch the same area on both arms. Ask where the patient feels your touch. Normally, both touches are felt. If the patient is experiencing sensory neglect, stimuli are ignored on one side of the body even if the primary senses are intact. In extinction to double simultaneous stimulation, patients will correctly identify a touch if the affected side is touched individually but will sense the touch only on the unaffected side if both sides are touched simultaneously. Lesions in the cerebral hemisphere may cause extinction of the contralateral side, particularly lesions in the right parietal lobe or right basal ganglia (Bickley et al., 2021). You can also perform this test on the face and legs.

These tests are simple to perform and provide a great deal of information on your patient’s neurologic status. Practice and integrate these discriminative sensation tests into your neurologic assessments.

References:

Bickley, L. S., Szilagyi, P. G., Hoffman, R. M., & Soriano, R. P. (2021). Bate’s Guide to Physical Examination and History Taking (13th ed.). Wolters Kluwer Health: Philadelphia.
 
Gelb, D. (2022, July 1). The detailed neurologic examination in adults. UpToDate. https://www.uptodate.com/contents/the-detailed-neurologic-examination-in-adults
 
Hinkle, J. (2021). Brunner & Suddarth’s Textbook of Medical-Surgical Nursing (15^th ed.). Wolters Kluwer Health.  https://wolterskluwer.vitalsource.com/books/9781975161057