Peripheral neuropathy is a medical condition that involves damage to the nerves outside of the brain and spinal cord. These peripheral nerves transmit sensory information, carry motor commands, and regulate involuntary functions like heart rate and digestion. Because the peripheral nervous system is so extensive, the physical indicators of damage can be diverse, ranging from numbness to muscle weakness. A detailed physical examination is the initial step in diagnosing this condition, allowing a clinician to identify which nerve fibers are affected and the overall pattern of nerve damage.
Assessing Sensory Changes
Sensory nerve fibers are typically the longest in the body, making them vulnerable to damage, which is why sensory symptoms often appear first in the feet and hands. The physical examination evaluates both large and small sensory fibers, as damage to each type produces distinct findings. Testing large-diameter nerve fibers, which transmit signals for vibration and position sense, is performed using a 128-Hz tuning fork. The ability to perceive the fork’s vibration is tested over bony prominences, beginning distally at the big toe or ankle and moving proximally.
Loss of vibratory perception is a common early sign of large-fiber neuropathy. Position sense, or proprioception, is tested by moving a joint, usually the big toe, up or down and asking the patient to identify the direction without looking. Impaired proprioception can lead to sensory ataxia, which is a noticeable unsteadiness in gait. Light touch and pressure sensation are assessed using a soft wisp of cotton wool or a nylon monofilament pressed against the skin until it bends.
A hallmark pattern of sensory loss is the “stocking-glove” distribution, where reduced sensation is symmetrical and primarily affects the feet and then the hands, resembling where stockings and gloves would cover the limbs. This pattern occurs because the longest nerves, which extend to the extremities, are affected first in many common types of neuropathy. Evaluating small-diameter nerve fibers, which transmit pain and temperature signals, is done using a sharp object like a pinprick or the cold surface of a tuning fork. A reduced ability to feel the pinprick or differentiate between hot and cold suggests damage to these small, thinly myelinated or unmyelinated fibers.
Evaluating Muscle Strength and Reflexes
Motor findings point to damage of the motor nerve fibers, which control muscle movement. Muscle strength is systematically graded on a scale, commonly from 0 (no movement) to 5 (normal strength against full resistance). Neuropathy typically causes distal weakness first, meaning it affects muscles furthest from the torso, such as those that lift the foot or control the fingers.
Foot drop, the inability to lift the front part of the foot, is a common and observable sign of motor neuropathy. The distribution of weakness is often symmetrical, affecting both sides of the body equally. Observable shrinking of muscle tissue, known as atrophy or wasting, is a sign of chronic motor nerve damage due to the lack of continuous nerve stimulation. The intrinsic muscles of the hands and the extensor digitorum brevis muscle on the top of the foot are often visually inspected for early signs of muscle wasting.
The physical exam also assesses deep tendon reflexes (DTRs), which are involuntary muscle contractions triggered by tapping a tendon. Neuropathy frequently results in diminished or absent reflexes, called hyporeflexia or areflexia. The ankle jerk reflex is often the first to be lost in polyneuropathies. The loss of reflexes indicates a problem along the lower motor neuron pathway.
Observing how a person walks, or gait analysis, provides visual evidence of motor and sensory impairment. Motor weakness, such as foot drop, can cause a “steppage” gait where the patient lifts the knee high to prevent the foot from dragging. Sensory loss affecting proprioception can lead to a broad-based, unsteady, or staggering gait, as the patient cannot accurately sense the position of their feet on the ground.
Recognizing Autonomic and Skin Indicators
Damage to the autonomic nerve fibers, which regulate involuntary bodily functions, produces distinct physical signs. These nerves control processes like heart rate, blood pressure, digestion, and sweating. Monitoring blood pressure when a patient moves from lying down to standing is a simple but important test for autonomic neuropathy. A significant drop in blood pressure upon standing, known as postural hypotension, can cause dizziness and is an indicator of autonomic involvement.
The physical examination also reveals trophic changes, which are long-term alterations in the skin, hair, and nails caused by chronic nerve damage and impaired blood flow regulation. Affected limbs may show dry, scaly skin, or a noticeable decrease in hair growth. Nails can become brittle or thickened due to the lack of proper nerve supply to the small blood vessels and sweat glands in the area.
Another observable indicator is the development of non-healing skin ulcerations, particularly on the feet. The loss of pain and temperature sensation means minor injuries go unnoticed and untreated, leading to chronic wounds. Abnormal sweating patterns may also be observed, such as excessive sweating in one area compensating for a complete lack of sweating in a denervated area. These subtle skin and vascular changes provide evidence of small-fiber and autonomic nerve dysfunction.