Source:Tracey A. Milligan, MD; Tamara B. Kaplan, MD; Neurology, Brigham and Women's/Massachusetts General Hospital, Boston, Massachusetts, USA
A complete sensory examination consists of testing primary sensory modalities as well as cortical sensory function. Primary sensory modalities include pain, temperature, light touch, vibration, and joint position sense. Sensation of the face is discussed in the videos Cranial Nerves Exam I and II, as are the special senses of smell, vision, taste, and hearing. The spinothalamic tract mediates pain and temperature information from skin to thalamus. The spinothalamic fibers decussate (cross over) 1-2 spinal nerve segments above the point of entry, then travel up to the brainstem until they synapse on various nuclei in thalamus. From the thalamus, information is then relayed to the cortical areas such as the postcentral gyrus (also known as the primary somatosensory cortex). Afferent fibers transmitting vibration and proprioception travel up to medulla in the ipsilateral posterior columns as fasciculus gracilis and fasciculus cuneatus, which carry information from the lower limbs and upper limbs, respectively. Subsequently, the afferent projections cross over and ascend to the thalamus, and from there to the primary somatosensory cortex.
The pattern of a sensory loss can help to localize the lesion and determine the diagnosis. For example, testing the primary modalities allows the examiner to distinguish between a length-dependent peripheral neuropathy (e.g., in diabetic patients), a radiculopathy from a possible cervical or lumbar herniated disc, or a dermatomal sensory level (e.g., in a spinal cord lesion).
In order to localize the sensory deficit, knowledge of neuroanatomy and the peripheral nervous system is crucial. When seeing a patient with a peripheral sensory deficit, it can be helpful to think about what nerve root(s) may be involved. A spinal nerve root arises from every spinal segment and consists of both a sensory dorsal root and a motor ventral root, which provide innervation to a specific dermatome and myotome, respectively. There are 31 paired spinal nerve roots: eight cervical, 12 thoracic, five lumbar, five sacral, and one coccygeal.
For example, the C5 through T1 roots form a network called the brachial plexus that controls movement and sensation in the upper limbs, including the shoulder, arm, forearm, and hand. The brachial plexus gives rise to the radial, median, and ulnar nerves. The median nerve carries sensation from all fingers except the fifth finger and half of the fourth, which are carried by the ulnar nerve. These nerve territories extend proximally on the palmar side of the hand. The ulnar and radial nerves carry sensory information from the dorsal side of the hands.
In the lower extremities, T12-L4 form the lumbar plexus, and L4-S4 form the sacral plexus. These plexi give rise to peripheral nerves. A few of these peripheral nerves are the femoral, obturator, and sciatic nerves (motor and sensory) and the lateral femoral cutaneous nerve (sensory only). The sciatic nerve gives rise to the tibial and common peroneal nerves. Use of a dermatomal and peripheral nerve map can be helpful in localizing sensory dysfunction in both the upper and lower extremities.
If primary sensory modalities are normal, cortical sensation (or higher order aspects of sensation) can be tested as well. Cortical sensation is tested when there is reason to suspect a disorder of the brain. Cortical sensory testing can assist with localization of nervous system disorders. The cortical sensory examination includes tests for tactile localization (extinction), stereognosis, graphesthesia, two-point discrimination, and point localization. Cortical sensory testing is not routinely done during a screening neurological examination.
In a screening sensory examination, light touch, pain, and vibration are tested in the feet. The sensory examination is expanded in a patient with a complaint referable to the nervous system, or if other components of the examination are abnormal.
1. Primary sensory testing
Begin primary sensory testing by asking the patient if there is any change in sensation in the body. The patient can describe and demarcate the sensory changes to aid in the evaluation.
- Light touch
- Using the tip of your finger or a piece of cotton, touch rather than stroke the patient's skin. Ask the patient to close eyes and tell you when the touch is felt.
- Explain that you will be touching the patient with either the sharp or dull end of a safety pin, but it should not hurt.
- With the patient's eyes closed, touch the hand, thumb and fingers with the sharp end of the pin but include a dull stimulus as well. With each touch, ask the patient to determine if the stimulus is "dull" or "sharp." Then move up the arm using the same technique.
- Repeat on the other hand and arm, and compare between the sides.
- Repeat pinprick on the anterior side of the chest wall and compare the sides.
- Test the pain sensation in the lower extremities, beginning distally in the feet and comparing between symmetric areas on the two sides of the body and between the distal and the proximal areas.
- If an area of numbness is found on the patient, begin testing at the numb area and work outward. Instruct the patient to say "yes" when feeling the normal pinprick sensation. Try to assess if there is a dermatomal pattern of sensory loss, which may be seen with a peripheral nerve injury.
Use the tuning fork as a cold stimulus to test temperature sensation. Test tubes containing warm and cold water could be used as stimuli, but this is not usually done. Temperature sensation should replicate the findings found on the pain sensation examination. Typically only one or the other is performed.
- Test the temperature sensation by touching the patient's skin with the tuning fork over the extremities in the same way the pain sensation is tested.
- Compare between the sides and between the proximal and distal areas of the same extremity.
- Use a low-pitched tuning fork of 128 Hz and strike the tines against the heel of your hand to produce a vibration.
- Place the stem of the tuning fork on the patient's great toe,
- Ask the patient to tell you when the vibration is no longer felt. Let the vibration fade until the patient no longer detects it, then apply the tuning fork to your own thumb to see if you still feel any vibration. To make the vibration decrease faster, run your finger along the tines to dampen the vibration.
- If the patient cannot feel the vibration in the toes at all, repeat the test by placing the fork over the medial malleolus and, if not felt there, move the fork over the patella.
- Record the most distal level where the stimulus is felt.
- Compare the two sides.
- If there was decreased vibration appreciation found on examination of the lower extremities, test if the vibration can be appreciated in the fingers.
- Hold the patient's large toe on the sides and demonstrate the test by moving the toe upward and downward while saying, "This is moving it up, and this is moving it down."
- Then instruct the patient to close the eyes and to correctly identify the direction as you move the toe up and down in a random order.
- Repeat the same on the other side. If the patient cannot correctly identify movements of even large excursions, attempt to move the foot up and down around the ankle joint.
- Normally, people are able to identify even a few degrees of movement. If any indication of abnormality is present, test the position sense in the fingers at the metacarpophalangeal joints.
2. Cortical sensation
- Tactile localization (double simultaneous stimulation; extinction).
- With the patient's eyes closed, ask the patient to localize where you have touched. Initially, touch the side that you are concerned may have a deficit to confirm that sensation to light touch is intact. Then, simultaneously touch both sides and ask the patient to identify where and how many places were touched.
- Touch the patient on one arm and then simultaneously on both arms. Do the same with the legs.
- Extinction of the stimulus on one side may be a sign of a lesion in the contralateral parietal cortex.
- If there are suspected lesions of the sensory cortex, additional testing may be performed, including two-point discrimination, point localization, and looking for any asymmetry of optokinetic nystagmus.
- Stereognosis tests the patient's ability to identify a common object (e.g., nickel, dime, quarter, penny, key, paper clip) placed in the hand.
- Ask the patient to close the eyes and then identify the small object in the hand. The patient may move the object around in the hand to feel it.
- Test the other hand in the same way. Importantly, the patient may not transfer the object from hand to hand. The patient should be able to identify it with one hand at a time. Patients should be able to differentiate coins, so it is not an acceptable answer to say "coin." The patient should be able to correctly determine a "nickel" or "quarter."
- Graphesthesia tests the ability to identify numbers or letters drawn on the patient's hand.
- Ask the patient to close the eyes. Use the blunt end of a pen to draw a large rendition of a number from 0-9 on the patient's palm. Make sure that the number is facing the patient and not you.
- Ask the patient to identify the number. Allow several trials.
- Test the hand that you think is not affected first. Then, repeat on the other side. Inability to correctly identify numbers may be indicative of a lesion in the contralateral parietal cortex.
A complete sensory examination consists of testing primary sensory modalities as well as cortical sensory function. Primary sensory modalities include pain, temperature, light touch, vibration, and joint position sense, or proprioception. While cortical sensory testing examines the higher order aspects of sensation, like identifying an object only with the help of touch. The pattern of sensory loss detected during this exam can help in the diagnosis of conditions like peripheral neuropathy, radiculopathy or cortical lesions.
Here, we will first briefly review the two major sensory pathways, and discuss the peripheral sensory nerve distribution. Then, we'll demonstrate the steps involved in testing primary modalities and cortical sensory function assessment.
Let's begin by revisiting the anatomy of the sensory tracts. The two major sensory pathways are the posterior column-medial lemniscus pathway and the spinothalamic tract. These paths involve first order, second order and third order neurons. The information relayed between these neurons ultimately reaches the postcentral gyrus, also known as the primary somatosensory cortex, which is a prominent structure in the parietal lobe.
The posterior column-medial lemniscus pathway is responsible for sensations like vibration, conscious proprioception, and discriminative, fine touch. The first order afferent neurons of this pathway carry information from the mechanoreceptors and proprioceptors all the way up to the medulla oblongata. Here they synapse with the second order neurons, which decussate, or crossover, and travel to the thalamus. From there, the third order neurons carry the information to the postcentral gyrus.
The spinothalamic tract works in a similar fashion, and relays information related to pain, temperature and crude touch. The first order neurons of this tract carry information from receptors like the nociceptors and thermoceptors. However, these neurons synapse at the spinal level. The second order neurons decussate in the spinal cord itself and relay the information all the way to the thalamus. And from there the third order neurons ultimately convey the message to the somatosensory cortex.
After discussing the tracts, let's briefly review the peripheral sensory nerve distribution, an understanding of which is necessary for interpreting the physical findings of a sensory exam. The peripheral sensory nerves arise from single or multiple spinal nerve roots. Each of these nerve roots provides sensory innervation to a specific region on the skin known as the dermatome creating a pattern known as the dermatome map. Since most of the peripheral sensory tests are focused on the upper and lower extremities, it is helpful to know the dermatome pattern of these regions in a bit more detail.
The C5 through T1 spinal nerve roots form a network called the brachial plexus, which sub-divides into peripheral nerves namely the musculocutaneous, axillary, radial, median, ulnar, medial antebrachial and medial brachial nerve. Together, they innervate and carry sensory information from different dermatomes of the volar and dorsal arm and hand. Knowledge of this map may be helpful in localizing sensory dysfunction in this region.
Similarly, roots T12 to S4 form the lumbosacral plexus, which gives rise to the peripheral nerves: lateral cutaneous, posterior cutaneous, obturator, femoral, common fibular and tibial nerve. These projections innervate different leg and foot areas -- anteriorly and posteriorly. A mental picture of this map while conducting a sensory test can aid in interpretation of the physical exam findings.
Now that we have an understanding of the sensory pathways and dermatomes, we can move onto the assessment of primary sensory modalities. During a screening sensory examination, light touch, pain, and vibration are tested in the feet. One should expand the examination to other regions if the patient has a complaint referable to the nervous system, or if other components of the neurological examination are abnormal.
Begin by asking the patient if they have been experiencing any change in sensation throughout their body. The patient can describe and demarcate the sensory changes to aid in the evaluation. Examine light touch sensation by asking the patient to close their eyes and instructing them to tell you when they feel your touch. Using the tip of your finger, lightly touch the patient's skin in different dermatomes.
Next, for pain testing, inform the patient that you will be touching their body with either the sharp or the dull end of a safety pin. Assure them that it will not hurt. Ask the patient to close their eyes again. Using the sharp and dull ends, test the sensation in both feet. Each time you touch, ask the patient to determine if the stimulus is "dull" or "sharp". Then, using just the sharp side, continue up the legs to make sure that the sensation does not get sharper proximally. At any point if the patient reports an area of numbness or no sensation, begin to work outwards from the numb point till the patient says, "yes", they feel normal pinprick sensation. Using a grease pencil, you can outline the area of numbness to determine if there is a dermatomal pattern of sensory loss, which may be seen with peripheral neuropathy.
Next, test the temperature sensation using a tuning fork as the cold stimulus. Touch the patient's skin with the fork over their extremities in the same manner as the pain sensation test, and ask them what sensation do they feel. Compare between the sides and between the proximal and distal areas of the same extremity.
Subsequently, test for vibration using a low-pitched tuning fork of 128 Hz frequency. Strike the tines against the heel of your hand to produce a vibration, and place the stem on the patient's big toe. Instruct the patient to tell you when they can no longer feel the vibration. Allow the vibration to fade, or to dampen it faster run your finger along the tines. As soon as the patient notifies, place the fork against your own thumb to see if you still feel the vibration. If they cannot feel the vibration in their toes at all, repeat the test by placing the tuning fork over the medial malleolus and, if not felt there, move over to the patella. Note the most distal location where vibration is felt by the patient, and compare the two sides. If there was decreased vibration appreciation found in the lower extremities, test if it can be appreciated in the fingers.
Finally, assess the proprioception or joint sense. Hold the patient's large toe on the sides and demonstrate the test by moving it upward and downward. Then instruct the patient to close their eyes and ask them to correctly identify the direction of toe movement. In no specific order, move the toe up and down. Repeat the test on the other side. If the patient cannot correctly identify your movements, attempt to move their foot up and down around the ankle joint. Normally, people are able to identify even a few degrees of movement. If any indication of abnormality is present, test the position sense in the fingers at the distal interphalangeal joints. This concludes the testing of the primary sensory modalities.
Now let's discuss a few commonly performed tests that examine cortical sensory functioning. A clinician should perform these only when there is a reason to suspect a brain disorder, as the findings can assist with lesion localization. This is not routinely done during a screening neurological exam.
The first test is called tactile localization. Instruct the patient to close their eyes, and ask them to localize where you have touched them. Initially, touch the side that you are concerned about -- to confirm that sensation to light touch is intact. Then, simultaneously touch both sides and ask the patient to identify the number and location of places they felt the sensation. Repeat the same test on the legs. Extinction of the stimulus on one side may be a sign of a lesion in the contralateral parietal cortex.
Next, conduct the stereognosis test, which assesses the patient's ability to specifically identify a common object, like a nickel or a quarter, just using their touch sensation. Request the patient to close their eyes and then identify the object in their hand. The patient may move it around to feel it, but they may not transfer the object from one hand to the other. Test the other hand in the same way with a different object. Patients should be able to differentiate coins, so it is not an acceptable answer to say "coin." The patient should be able to correctly determine whether it's a "nickel" or a "quarter."
Lastly, conduct the graphesthesia test, which is another method for assessing cortical functioning. Ask the patient to close their eyes and extend their arm with palm facing up. With the tip of a pen, draw a number from zero to nine on the patient's palm. Make sure that the number is facing the patient and not you. Ask them to identify the number. Repeat the test on the opposite hand. Inability to correctly identify numbers may be indicative of a lesion in the contralateral parietal cortex.
"This concludes general sensory testing, which is the most subjective portion of the neurological exam, and requires patient's cooperation and full effort. There are other ways to examine the sensory system, including two-point discrimination, which tests the ability of a patient to differentiate one stimulus from two. Overall, the sensory examination demands vigilance on the part of the examiner to make sure the patient is providing accurate and honest answers. Be suspicious of sensory findings that do not fit anatomical patterns, or those that may not correlate with the more objective findings seen during other sections of the neurological examination. Any abnormal results of sensory testing need to be correlated with the results from other parts of the neuro exam to ensure and determine the pattern of abnormality."
You have just watched a JoVE video describing the sensory examination. In this presentation, we revisited the anatomy of the major sensory pathways, and the dermatomes. Then, we discussed the steps for examining primary modalities as well as a few tests for cortical functioning assessment. As always, thanks for watching!
Applications and Summary
The sensory part of the neurological examination is the most subjective portion of the exam, and requires a patient's cooperation and full effort. It requires vigilance on the part of the examiner to make sure the patient is providing accurate and honest answers. Be suspicious of sensory findings that do not fit anatomical patterns, or those that may not correlate with the more objective findings seen on the other sections of the neurological examination.
Any abnormal results of the sensory examination need to be correlated with the results of the other parts of the neurological examination to determine the pattern of abnormality. Abnormalities of reflexes may provide a level in the nervous system that may be confirmed by a pattern of a dermatomal sensory level, which helps to localize a lesion.