Symptoms are related to the type of nerves affected.
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Motor nerve damage is most commonly associated with muscle weakness. Other symptoms include painful cramps, fasciculations (uncontrolled muscle twitching visible under the skin) and muscle shrinking.
Sensory nerve damage causes various symptoms because sensory nerves have a broad range of functions.
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Damage to large sensory fibers harms the ability to feel vibrations and touch, especially in the hands and feet. You may feel as if you are wearing gloves and stockings even when you are not. This damage may contribute to the loss of reflexes (as can motor nerve damage). Loss of position sense often makes people unable to coordinate complex movements like walking or fastening buttons or maintaining their balance when their eyes are shut.
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The “small fibers” without myelin sheaths (protective coating, like insulation that normally surrounds a wire) include fiber extensions called axons that transmit pain and temperature sensations. Small-fiber polyneuropathy can interfere with the ability to feel pain or changes in temperature. It is often difficult for medical caregivers to control, which can seriously affect a patient’s emotional well-being and overall quality of life. Neuropathic pain is sometimes worse at night, disrupting sleep. It can be caused by pain receptors firing spontaneously without any known trigger, or by difficulties with signal processing in the spinal cord that may cause you to feel severe pain (allodynia) from a light touch that is normally painless. For example, you might experience pain from the touch of your bedsheets, even when draped lightly over the body.
Autonomic nerve damage affects the axons in small-fiber neuropathies. Common symptoms include excess sweating, heat intolerance, inability to expand and contract the small blood vessels that regulate blood pressure, and gastrointestinal symptoms. Although rare, some people develop problems eating or swallowing if the nerves that control the esophagus are affected.
There are several types of peripheral neuropathies, the most common of which is linked to diabetes. Another serious polyneuropathy is Guillain-Barre syndrome, which occurs when the body’s immune system mistakenly attacks the nerves in the body. Common types of focal (located to just one part of the body) mononeuropathy include carpal tunnel syndrome, which affects the hand and the wrist, and meralgia paresthetica, which causes numbness and tingling on one thigh. Complex regional pain syndrome is a class of lingering neuropathies where small-fibers are mostly damaged.
The bewildering array and variability of symptoms that neuropathies can cause often makes diagnosis difficult. A diagnosis of neuropathy typically includes:
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Medical history. A doctor will ask questions about symptoms and any triggers or relieving factors throughout the day, work environment, social habits, exposure to toxins, alcohol use, risk of infectious diseases, and family history of neurological diseases.
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Physical and neurological exams. A doctor will look for any evidence of body-wide diseases that can cause nerve damage, such as diabetes. A neurological exam includes tests that may identify the cause of the neuropathic disorder as well as the extent and type of nerve damage.
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Body fluid tests. Various blood tests can detect diabetes, vitamin deficiencies, liver or kidney dysfunction, other metabolic disorders, infections and signs of abnormal immune system activity. Less often other body fluids are tested for abnormal proteins or the abnormal presence of immune cells or proteins associated with some immune-mediated neuropathies.
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Genetic tests. Gene tests are available for some inherited neuropathies.
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Additional tests may be ordered to help determine the nature and extent of the neuropathy.
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Physiologic tests of nerve function
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Nerve conduction velocity (NCV) tests measure signal strength and speed along specific large motor and sensory nerves. They can reveal nerves and nerve types affected and whether symptoms are caused by degeneration of the myelin sheath or the axon. During this test, a probe electrically stimulates a nerve fiber, which responds by generating its own electrical impulse. An electrode placed further along the nerve’s pathway measures the speed of signal transmission along the axon. Slow transmission rates tend to indicate damage to the myelin sheath, while a reduction in the strength of impulses at normal speeds is a sign of axonal degeneration. Inability to elicit signals can indicate severe problems with either.
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Electromyography (EMG) involves inserting very fine needles into specific muscles to record their electrical activity at rest and during contraction. EMG tests irritability and responsiveness, detects abnormal muscular electrical activity in motor neuropathy, and can help differentiate between muscle and nerve disorders.
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Neuropathology tests of nerve appearance
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Nerve biopsy involves removing and examining a sample of nerve tissue, usually a sensory nerve from the lower leg (called a sural nerve biopsy). Although a nerve biopsy can provide the most detailed information about the exact types of nerve cells and cell parts affected, it can further damage the nerve and leave chronic neuropathic pain and sensory loss.
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Neurodiagnostic skin biopsy allows specialists to examine nerve fiber endings following removal of only a tiny piece of skin (usually 3 mm diameter) under local anesthesia. Skin biopsies have become the gold standard for diagnosing small fiber neuropathies that don’t affect standard nerve conduction studies and electromyography.
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Autonomic testing
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Several different types of autonomic testing can evaluate peripheral neuropathies, one of which is a QSART test that measures the ability to sweat in several sites in the arm and leg. Abnormalities in QSART are associated with small fiber polyneuropathies
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Radiology imaging tests
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Magnetic resonance imaging (MRI) of the spine can reveal nerve root compression (“pinched nerve”), tumors, or other internal problems. MRI of the nerve (neurography) can show nerve compression.
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Computed tomography (CT) scans of the back can show herniated disks, spinal stenosis (narrowing of the spinal canal), tumors, bone and vascular irregularities that may affect nerves.
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Muscle and nerve ultrasound is a noninvasive experimental technique for imaging nerves and muscles for injury such as a severed nerve or a compressed nerve. Ultrasound imaging of the muscles can detect abnormalities that may be related to a muscle or nerve disorder. Certain inherited muscle disorders have characteristic patterns on muscle ultrasound.
Medical Information was referenced from the National Institute of Neurological Disorders and Stroke, the Mayo Clinic, and FFPN
