Micrograph showing peripheral neuropathy (vasculitis).Polyneuropathy is peripheral neuropathy occurring in the same area on both sides of the body.
|Classification and external resources|
Polyneuropathy (poly- + neuro- + -pathy) is damage or disease affecting peripheral nerves (peripheral neuropathy) in roughly the same areas on both sides of the body, featuring weakness, numbness, and burning pain. It usually begins in the hands and feet and may progress to the arms and legs; and sometimes to other parts of the body where it may affect the autonomic nervous system. It may be acute or chronic. A number of different disorders may cause polyneuropathy, including diabetes and some types of Guillain-Barré syndrome.Sensory polyneuropathy is the condition of having multiple sensory neuropathies, while motor polyneuropathy refers to multiple motor neuropathies, sensorimotor polyneuropathy is the combination of both conditions.[medical citation needed]
Polyneuropathies may be classified in different ways, such as by cause, by speed of progression, or by the parts of the body involved. Classes of polyneuropathy also are distinguished by which part of the nerve cell is affected mainly: the axon, the myelin sheath, or the cell body.
- Distal axonopathy, or "dying-back neuropathy", is the result of some metabolic or toxic derangement of neurons. It is the most common response of neurons to metabolic or toxic disturbances, and may be caused by metabolic diseases such as diabetes, kidney failure, connective tissue disease, deficiency syndromes such as malnutrition and alcoholism, or the effects of toxins or drugs such as chemotherapy (chemotherapy-induced peripheral neuropathy). They may be divided according to the type of axon affected: large-fiber, small-fiber, or both. The most distal portions of axons are usually the first to degenerate, and axonal atrophy advances slowly toward the nerve's cell body. If the cause is removed, regeneration is possible, although the prognosis depends on the duration and severity of the stimulus. People with distal axonopathies usually present with sensorimotor disturbances that have a symmetrical "stocking and glove" distribution. Deep tendon reflexes and autonomic nervous system functions also are lost or diminished in affected areas.
- Myelinopathy, or "demyelinating polyneuropathy", is due to a loss of myelin (or of the Schwann cells that make and contain it). This demyelination slows down or completely blocks the conduction of action potentials through the axon of the nerve cell. The most common cause is acute inflammatory demyelinating polyneuropathy (AIDP, the most common form of Guillain–Barré syndrome), although other causes include chronic inflammatory demyelinating polyneuropathy (CIDP), genetic metabolic disorders (e.g., leukodystrophy), and toxins.
- Neuronopathy is the result of destruction of peripheral nervous system (PNS) neurons. They may be caused by motor neurone diseases, sensory neuronopathies (e.g., Herpes zoster), toxins, or autonomic dysfunction. Neurotoxins such as the chemotherapy agent vincristine may cause neuronopathies.
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Acute polyneuropathy may have various causes, including infections, autoimmune reactions, toxins, certain drugs (especially chemotherapy agents), and cancer. When the cause cannot be determined it is called "idiopathic." With drug-induced polyneuropathy, there is a trade-off of risk, benefit, and adverse effects; for example, chemotherapy may cause problems (nausea, vomiting, polyneuropathy, and others), but survival may be longer with it than without it.Chronic polyneuropathy often is caused by diabetes mellitus or by the excessive alcohol consumption (alcoholic polyneuropathy), or by degeneration of connective tissue protecting the nerves as in connective tissue diseases,but a variety of other less common causes are known, including nutritional deficiencies, and liver or kidney failure.
Polyneuropathies usually are caused by processes that affect the body as a whole. Diabetes and impaired glucose tolerance are the most common causes. Other causes relate to the particular type of polyneuropathy, and there are many different causes of each type, including inflammatory diseases such as lyme disease, vitamin deficiencies, blood disorders, and toxins (including alcohol and certain prescribed drugs).
Diagnosis of polyneuropathies begins with a history and physical examination in order to document what the pattern of the disease process is (arms, legs, distal, proximal, symmetric), when they started, how long they have lasted, if they fluctuate, and what deficits and pain are involved. If pain is a factor, and it often is, determining where and how long the pain has been present is important. One also needs to know what disorders are present within the family and what diseases the patient may have. This is vital in forming a differential diagnosis.
Although diseases often are suggested by the physical examination and history alone, testing is still a large part of the diagnosis. Tests that may be employed include electrodiagnostic testing using electromyography, nerve conduction studies, muscle biopsy, serum creatine kinase (CK) and antibody testing. Nerve biopsy rarely is used to establish a diagnosis, but is helpful in determining small fiber neuropathy. Other tests may be used, especially tests for specific disorders associated with polyneuropathies.Quality measures have been developed to diagnose patients with distal symmetrical polyneuropathy (DSP).
There is a large differential for polyneuropathies: vitamin deficiency, cancer, toxins, infections (ex. Guillain–Barré syndrome, Lyme disease), liver disease, endocrine disease (including diabetes with diabetic and pre-diabetic neuropathy), amyloidosis, genetic disorders, motor neuron disorders, motor neuropathies, kidney failure, paraneoplastic, polio, porphyria (some types), neurosarcoidosis, spinal muscular atrophy, catecholamine disorders, psychological disorders and many others.
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Most types of polyneuropathy progress fairly slowly, over months or years, but rapidly progressive polyneuropathy also occurs. It is important to recognize that glucose levels in the blood may spike to nerve-damaging levels after eating even though fasting blood sugar levels and average blood glucose levels may still remain below normal levels (currently they typically are considered below 100 mg/dL for fasting blood plasma and 5.7% for HgbA1c, the test commonly used to measure average blood glucose levels over an extended period).
Studies have shown that many of the cases of peripheral small fiber neuropathy with typical symptoms of tingling, pain, and loss of sensation in the feet and hands are due to glucose intolerance before a diagnosis of diabetes or pre-diabetes. Such damage often is reversible, particularly in the early stages, with changes in diet, exercise, and weight loss.The treatment of polyneuropathies is aimed firstly at eliminating or controlling the cause, secondly at maintaining muscle strength and physical function, and thirdly at controlling symptoms such as neuropathic pain.If possible, treatment focuses on the underlying disease. Further, pain medications may be given and physical therapy is used to retain muscle function. Vyndaqel or Tafamidis is a European Medicines Agency approved drug for the treatment of familial amyloid polyneuropathy caused by transthyretin amyloisis.
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