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The central nervous system, apart from the brain and spinal cord, the nerves visible in the images are all peripheral nerves. Therefore, for our physical examination, the workload is actually very large and the difficulty is considerable. The peripheral nerves here include those of the upper limbs, lower limbs, and trunk, indicating the distribution of peripheral nerves, which is also the target of our examination.
2022-12-04 ANDs ANDs posted in Anhui Province
The central nervous system, apart from the brain and spinal cord, the nerves visible in the images are all peripheral nerves. Therefore, for our physical examination, the workload is actually very large and the difficulty is considerable. The peripheral nerves here include those of the upper limbs, lower limbs, and trunk, indicating the distribution of peripheral nerves, which is also the target of our examination.
Today we are sharing content about the physical examination of peripheral neuropathy. Before discussing this topic, let’s clarify the purposes of the physical examination for peripheral neuropathy. I have summarized the following four purposes: to confirm clinical findings, detect clinical occult findings, answer four questions, and assist clinical diagnosis.
As mentioned, apart from the central nervous system—brain and spinal cord—the nerves visible in the images are all peripheral nerves. Therefore, for our examination, the workload is large and the difficulty considerable. The peripheral nerves include those in the upper limbs, lower limbs, and trunk, indicating the distribution of peripheral nerves, which is also the target of our examination.
Firstly, let’s see what is meant by confirming clinical findings. Our diagnostic process starts from patient admission and history taking. For example, when a patient says they have experienced weakness, numbness in hands or feet, or unsteady gait during a period, we need to confirm through physical examination whether there is weakness, sensory reduction, deep sensory disturbance, or ataxia. Another example is when a patient tells us which parts are numb, such as hand numbness, where exactly, or foot numbness, where exactly. We need to observe the affected areas; this is called confirming clinical findings. Secondly, detecting clinical occult findings. After hearing the patient’s complaints, through our examination, if we discover clues beyond what the patient reported, this is the detection of clinical occult findings via physical examination. Thirdly, through physical examination, we should answer four questions often asked in clinical practice regarding peripheral neuropathy: First, is the neuropathy motor, sensory, or mixed? Second, is it symmetrical or asymmetrical? Third, is it primarily an axonal damage, demyelination, or mixed? Fourth, is it an all-or-none pattern? Meaning, does it affect large myelinated fibers, thin myelinated fibers, or unmyelinated fibers, and is it total or partial damage?
Answering these four questions through physical examination essentially helps us to localize the lesion. That is, the physical examination first confirms whether there is peripheral nerve damage, then identifies which part of the peripheral nerve is damaged, completing clinical localization. Meanwhile, physical examination can also provide qualitative information. For example, if our examination identifies a single nerve neuropathy mainly involving the distal ulnar nerve, we may consider it compression-related. If there are multiple single nerve neuropathies accompanied by pain in a young female, vascular inflammation neuropathy may be first considered. If it’s an acute, multifocal peripheral neuropathy, we consider the possibility of GBS (Guillain-Barré Syndrome). Therefore, the purpose of physical examination in peripheral neuropathy is to help us determine clinical clues, as well as for localization and qualitative assessment.
When discussing the physical examination of peripheral nerves, we often display a diagram like this because it is closely related to peripheral nerve localization, and helps us answer the four questions mentioned earlier. What does the peripheral nerve physical examination involve? First, examination of the motor system; second, the sensory system; and finally, the autonomic nervous system. Since the motor system has a significant weight in myopathy physical examination, related to muscle strength, muscle tone, tendon reflexes, etc., these will be covered later in Teacher Song’s micro-lecture, so they are not elaborated here. Today, we focus on sensation and autonomic nerves, as well as some special signs that may be seen in peripheral nerves.
What does sensory system examination involve? As shown, tactile sensation, vibration sense, and position sense relate to large myelinated fibers. Next, pain and temperature sensation relate to thin myelinated and unmyelinated fibers. Additionally, there is the autonomic nervous system.
Let’s elaborate. Sensory examination includes light touch, pinprick sensation, temperature sensation, vibration sense, position sense, two-point discrimination, graphesthesia, and stereognosis. You may wonder, why check sensations 6, 7, and 8? Aren’t two-point discrimination, graphesthesia, and stereognosis cortical sensations? Why include them in peripheral nerve examination? This will be explained shortly.
Next, let’s explain how to perform these sensory examinations one by one. First, light touch examination. What tools do we use for light touch? Most common is a cotton swab, also percussion hammer with a small brush at the end, or the classic monofilament nylon filament. How to perform light touch? Lightly touch the patient’s skin with a cotton swab and immediately withdraw, then ask the patient if they feel something. An important point: when performing light touch, often people pull out some cotton fibers and sweep on the skin, but this is incorrect. Do not brush back and forth; only gently touch. This also applies using a small brush—lightly tap the skin and ask if they feel it, not brush repeatedly. The monofilament nylon filament is a calibrated tool to quantitatively assess touch sensation. Regardless of the tool, it should be perpendicular at 90 degrees to the skin during testing. Also, all sensation tests must be performed with comparison between both sides. For simplicity, this bilateral comparison principle will not be repeatedly mentioned later.
Second, pinprick sensation test. Tools can be a needle, such as pins or safety pins. Testing involves stimulating the skin along the distribution of a single nerve and/or horizontally moving the needle point. What does this mean? For example, if clinical clues suggest a single nerve lesion, we will examine the distribution area of that nerve, find borderlines of hypoesthesia or anesthesia, then check other areas to confirm whether it is indeed a single nerve lesion. Horizontal shifting means in cases suspected of polyneuropathy, typically symmetric glove-and-stocking distribution, we examine from distal to proximal or vice versa to find the glove or stocking borders - this is horizontal shifting examination.
In single nerve or horizontal tests, note that the stimulus should be in one direction: proximodistal or distoproximal. The general principle is to move from areas of reduced or lost pinprick sensation to areas of normal or sensitive pinprick sensation. The purpose of pinprick testing is to identify areas with reduced or increased pain sensation, aiding in lesion localization. Note that some patients may exhibit reduced pinprick sensation distally on one limb but normal proximally, while on the other limb show pain hypersensitivity distally and normal proximally. Then we need to adopt the appropriate test direction accordingly: from distal to proximal when there is loss, and from proximal to distal if there is hypersensitivity.
Third, temperature sensation test. For clinicians, the most convenient tool is a tuning fork. We can also use ice packs, ice cubes, or heating pads. But in terms of convenience, tuning forks are easiest. For example, tuning forks are often cold in winter, so no special processing is needed. Even in summer, because we work in air-conditioned environments, tuning forks remain cool and need no further preparation. In special cases, cooling the tuning fork slightly before testing may be done. Human body temperature is approximately 36-37°C; cold is perceived below ~33°C, and below 15°C feels very cold.
When the temperature presented to patients is around 35-39°C, they perceive warmth, above 39°C it causes pain, and above 45°C the skin can be damaged. So temperature sensation tests should be within safe temperature ranges. Cold sensation and heat sensation tests target different fiber types: cold sensation is mediated by thin myelinated fibers, heat by unmyelinated fibers; thus damage affects different fiber types, although both are referred to as temperature sensation.
Fourth, vibration sense. The tool is a 128 Hz tuning fork. Two types are shown: one with a blue base on the right, and one with a green base on the left. The green-headed tuning fork on the left is commonly used for qualitative judgment of vibration sense reduction. The blue one on the right is a quantitative tuning fork.
To test vibration sense: gently strike the tuning fork arms and place the base on bony prominences. Several points need attention because improper technique can affect judgment. Hold the short handle with the thumb, index, and middle fingers, with the base sitting firmly on the patient’s bony landmark.
When holding, do not touch the tuning fork’s arms as this dampens vibration. Testing is performed from distal to proximal sites, e.g., starting from the distal interphalangeal joint of the big toe, moving proximally to the ankle, knee, then anterior superior iliac spine or higher.
How long should the tuning fork vibrate? For those under 60 years old, vibration sense usually disappears by 12 seconds; for those above 60, vibration disappears in about 10 seconds — reflecting natural aging of peripheral nerves, their density, and health differences before and after age 60.
Fifth, position sense (also called proprioception). The tool is simple: the examiner’s thumb and index finger. The method is to gently grasp the first joint of the patient’s finger or toe on both sides, avoiding the top which has tactile sensation influence. Then, move the joint slightly up or down, with the patient’s eyes closed. If slight movement can’t be perceived, increase the movement amplitude. If still unperceived, move to the proximal large joints such as wrist, elbow, shoulder, or ankle and knee in the lower limb, and similarly perform small then larger movements.
Another very important physical sign in peripheral neuropathy is the Romberg sign, called “closed-eye imbalance test” in Chinese. How to do a proper Romberg test? The patient stands upright with arms down by sides, feet approximately 20 cm apart, then closes eyes and is gently pushed on the chest. This differs from the usual method. If unstable or losing balance, it indicates a positive Romberg sign; if patient is unstable with eyes open, consider cerebellar lesion, which is well used clinically.
It is important to have a “love injury” mindset. If patients have symptoms such as “I walk unsteadily,” “feet feel like walking on cotton,” or “difficulty going to the bathroom after turning off lights at night,” these suggest possible positive Romberg sign. In such cases, protection must be provided to prevent falls.
Next is cortical sensation testing. First, two-point discrimination. The tool is a two-point discriminator, an octagonal disk with one or two stimuli on each side spaced differently. The upper half of the image shows the varying sensitivity of body regions to two-point discrimination.
The most sensitive is the tongue, able to distinguish 1.1 millimeters difference, explaining why the tongue can detect tiny foreign bodies like fish bones well. The least sensitive area is the skin of the neck and back, requiring 6 centimeters to perceive two points separately. Why include cortical sensation here? Because abnormal two-point discrimination does not necessarily indicate central sensory damage.
Next, graphesthesia testing is done using the examiner’s finger or bamboo stick. The method is to write numbers, letters or characters on the patient’s skin, then ask them to identify, e.g., drawing an “8” and asking what it is.
Stereognosis (object recognition) test uses various easily operable small objects, avoiding large ones. The patient closes eyes, opens their palm, and the examiner places the object in their hand. The patient feels or holds it and tells what it is. Commonly used objects include keys, coins, pens, or combs.
We can see that two-point discrimination, graphesthesia, and stereognosis all belong to cortical sensations. Why place them here?
This relates closely to the anatomy of our sensory system. The sensory pathway is afferent (toward the center). The first-order neuron is located in the dorsal root ganglion of the spinal cord; the second-order neuron in the dorsal horn gray matter or the nucleus gracilis and cuneatus in the medulla; the third-order neuron is in the thalamus, projecting to the postcentral gyrus in the parietal cortex.
What does this imply? When we perform peripheral nerve examination, for patients with sensory neuron damage or severe numbness, they cannot well perceive two-point discrimination or stereognosis.
In such cases, cortical sensation deficits cannot directly localize central lesions. Therefore, when differentiating central versus peripheral causes, we must first confirm any peripheral nerve involvement. If peripheral nerve damage exists, cortical sensation deficits need careful interpretation to differentiate between central and peripheral causes.
After completing the examination and discovering various problems, we must integrate data and judge. Often, we differentiate from spinal cord lesions, especially in glove-and-stocking patterns versus spinal cord lesions, and between peripheral nerve and nerve root lesions. Briefly, spinal cord lesions involve sensory and motor impairments and bowel/bladder dysfunction. When combined with autonomic dysfunction, bladder/bowel issues also arise. Retention is more common in spinal cord lesions.
When we observe a condition like in the left image here, with symmetrical impairment on the lateral upper arm, we must be cautious. Clinically, multiple mononeuropathies or radiculopathies may be considered, requiring meticulous examination and comprehensive analysis for differential diagnosis.
This is a nerve root distribution chart related to sensory nerves. The facial sensory nerve is mainly the trigeminal nerve. It is important to note that C2 and C3 are cervical segments associated with sensation. C2 innervates the anterior neck and posterior occiput; C3 innervates the posterior neck.
This diagram shows nerve distributions. Through detailed physical examination, we carefully detect problems step by step: first, the type of damage; second, the distribution; finally, localization.
A common example is the hand. On the left figure, the dorsal radial side of the three fingers is innervated by the radial nerve; the two ulnar-side fingers by the ulnar nerve. On the palmar side, three and a half fingers are innervated by the median nerve; one and a half by the ulnar nerve. The dorsal side shows a 3+2 pattern; the palmar side 3.5+1.5. Corresponding nerve roots are identical: the thumb and index finger, both palmar and dorsal, are innervated by C6; the middle finger by C7; the ring and little fingers by C8.
Many physicians may have exposure to electromyography (EMG). When performing EMG for mononeuropathy, they not only consider whether it’s pure peripheral nerve lesion but also if there is radicular involvement, using further EMG to assist diagnosis. Physical examination for peripheral nerves performs a similar function—examining individual nerve territories to help distinguish mononeuropathy, radiculopathy, or other lesions.
Let’s briefly look at the lower limb. The distribution of peripheral nerves is even more complex, including nerve root distributions. This chart gives an overview; interested readers can study it in detail.
As mentioned, besides physical examination of large myelinated, thin myelinated fibers of peripheral nerves to help localization, autonomic nerves are very important. Autonomic nerve damage is often identified through clinical history, e.g., patients report diarrhea, constipation, reduced sweating, or dizziness, especially on standing. Such clues often suggest autonomic nerve damage. Can we use clinical or objective methods to detect autonomic dysfunction? Postural hypotension, arrhythmia, sweating abnormalities, and sympathetic nerve dysfunction can be tested.
Postural hypotension test involves measuring blood pressure changes from supine to standing. Standing does not have to be fully vertical; any angle above 60 degrees is considered upright. For patients too dizzy to get out of bed, raising the bed to above 60 degrees suffices. The test window is 3 minutes; a decrease of systolic blood pressure by over 20 mmHg or diastolic by over 10 mmHg is diagnostic. A question often raised is: how to judge in hypertensive patients? For special hypertensives, systolic drop over 30 mmHg is required.
This is the examination for a patient complaining of no sweating in the hand. How is it done? Using iodine and starch; please see the lower right image. Briefly, iodine is applied to the hand and allowed to dry, then starch is dusted on, then the hand is warmed to induce sweating. Question: which hand does not sweat? The answer: the right hand sweats, the left hand does not. Why? Here, iodine acts as a color indicator. When sweating, iodine and starch interact causing color change. The patient’s left hand cannot sweat, so no color change occurs. This test helps identify sweating or lack thereof. For autonomic anhidrosis, a good examination tool is a heating and insulation chamber where the patient lies down, which can detect the lesion location.
Horner syndrome is well known to us clinicians on the front line. Signs such as ptosis, miosis, and anhidrosis on the ipsilateral forehead can indicate damage to the descending sympathetic chain, helping us make a diagnosis. 
After discussing the examination of sensory and autonomic nerves, I want to emphasize that, in the examination of peripheral nerves, it is actually very important to use the doctor’s eyes. Traditional Chinese medicine often mentions “observation, listening, questioning, and pulse-taking,” with observation being the most important physical examination. So, what do we observe? We look at the patient’s skin color and complexion, gait, leg shape, soles, arches, etc. Let’s briefly describe these. 
For example, in patients with peripheral neuropathy, what is the most commonly observed gait? Peripheral neuropathy patients exhibit distal damage and length-dependent weakness. In the lower limbs, you can see foot drop; patients often say, “I easily trip when walking on flat ground.” Their gait will show a high-stepping walking pattern. Additionally, for patients with deep sensory deficits or sensory neuron involvement, a wide-based gait is often observed because they are prone to instability when walking, leading to this wide-based gait. Therefore, observing gait is very important.
Special signs are relatively familiar, such as in hereditary peripheral neuropathy, where you can see pes cavus, claw toes, and hammer toes; for diabetic peripheral neuropathy patients, distal lower limb skin pigmentation, skin changes, and skin malnutrition may be observed; also, skin ichthyosis-like changes, etc.
The illustration shows signs related to POEMS syndrome, where we can see nipple pigmentation, clear demarcation lines on the palms and backs of the hands, leukonychia, hemangiomas, vitiligo, and other manifestations.
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