Polyneuropathy

Polyneuropathy or symmetrical 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, pins-and-needles 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 (appearing suddenly, progressing rapidly and resolving slowly) or chronic (emerging and developing gradually). 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 or sensory-motor polyneuropathy is the combination of both conditions.

Classification

Polyneuropathies can be classified in different ways, such as by cause, by speed of progression, or by the parts of the body involved. Classes of polyneuropathy are also distinguished by which part of the nerve cell is mainly affected: 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, renal 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 can 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 towards the nerve's cell body. If the cause is removed, regeneration is possible, though 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 are also 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 Guillainâ€"Barré syndrome), though 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.

Evaluation

Evaluation and classification of polyneuropathies begins with a history and physical exam 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 often diseases are suggested by the physical exam and history alone, testing is still a large part of the diagnosis. Tests which may be employed include electrodiagnostic testing using electromyography, muscle biopsy, serum creatine kinase (CK), and antibody testing. Nerve biopsy is not used much, but is helpful in determining small fiber neuropathy. Other tests may be used, especially tests for specific disorders associated with polyneuropathies.

Causes

Acute polyneuropathy can 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 can be longer with it than without it.

Chronic polyneuropathy is often 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.

Treatment

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.

Differential diagnosis

There is a large differential for polyneuropathies: vitamin deficiency, cancer, toxins, infections (ex. Guillainâ€"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.