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Overview of polyneuropathy

Overview of polyneuropathy
Author:
Seward B Rutkove, MD
Section Editor:
Jeremy M Shefner, MD, PhD
Deputy Editor:
Richard P Goddeau, Jr, DO, FAHA
Literature review current through: Oct 2022. | This topic last updated: Aug 23, 2022.

INTRODUCTION — This topic will review the common causes, clinical presentation, diagnostic evaluation, and general management of polyneuropathy. Specific polyneuropathies are discussed in greater detail in individual topics.

TERMINOLOGY — The terms "polyneuropathy," "peripheral neuropathy," and "neuropathy" are frequently used interchangeably but are distinct.

Polyneuropathy is a specific term that refers to a generalized, relatively homogeneous process affecting many peripheral nerves, with the distal nerves usually affected most prominently.

Peripheral neuropathy is a less precise term that is frequently used synonymously with polyneuropathy, but can also refer to any disorder of the peripheral nervous system including radiculopathies and mononeuropathies.

Neuropathy, which again is frequently used synonymously with peripheral neuropathy and/or polyneuropathy, can refer even more generally to disorders of the central and peripheral nervous system.

The polyneuropathies must be distinguished from other diseases of the peripheral nervous system, including the mononeuropathies and mononeuropathy multiplex (multifocal neuropathy), and from some disorders of the central nervous system.

Mononeuropathy refers to focal involvement of a single nerve, usually due to a local cause such as trauma, compression, or entrapment. Carpal tunnel syndrome is a common example of a mononeuropathy.

Mononeuropathy multiplex refers to simultaneous or sequential involvement of noncontiguous nerve trunks. Used loosely, this term can refer to multiple compressive mononeuropathies. However, in its more specific meaning, it identifies multiple nerve infarcts due to a systemic vasculitic process that affects the vasa nervorum. (See "Clinical manifestations and diagnosis of vasculitic neuropathies".)

Diseases of the central nervous system such as a brain tumor, stroke, or spinal cord lesion occasionally present with symptoms that are difficult to distinguish from polyneuropathy. (See "Differential diagnosis of peripheral nerve and muscle disease".)

ETIOLOGY AND PATHOGENESIS — Polyneuropathy has a wide variety of causes, ranging from the common, such as diabetes mellitus, alcohol abuse, and HIV infection [1], to the rare, such as some unusual forms of Charcot-Marie-Tooth (CMT) disease. It often occurs as a side effect of medication or as a manifestation of systemic disease. The rate of progression of the polyneuropathy in conjunction with its character (axonal or demyelinating) can help identify its etiology (table 1A-C).

The peripheral nerves are susceptible to a variety of toxic, inflammatory, hereditary, infectious, and parainfectious factors that can impair their health and function, leading to the clinical disorder of polyneuropathy. Unfortunately, there are no simple rules to apply that can reliably distinguish the type of polyneuropathy (eg, demyelinating versus axonal, chronic versus acute, sensory versus motor) produced by these disease categories.

Diabetic — Diabetic polyneuropathy is generally considered predominantly axonal; however, variable degrees of demyelination are often present, at least electrophysiologically. The mechanism underlying the development of diabetic neuropathy is extremely complex and likely relates to inflammatory, metabolic, and ischemic effects. (See "Pathogenesis of diabetic polyneuropathy".)

Other systemic — Other systemic diseases generally cause predominantly axonal polyneuropathies. Examples of these include the polyneuropathies associated with the following conditions:

Longstanding HIV infection (see "Epidemiology, clinical manifestations, diagnosis, and treatment of HIV-associated distal symmetric polyneuropathy (HIV-DSPN)")

Critical illness (see "Neuromuscular weakness related to critical illness", section on 'Critical illness polyneuropathy')

End-stage kidney disease (see "Uremic polyneuropathy")

Amyloidosis (see "Overview of amyloidosis", section on 'Neurologic abnormalities')

Hypothyroidism (see "Clinical manifestations of hypothyroidism", section on 'Neurologic dysfunction')

Vitamin deficiencies (see "Overview of water-soluble vitamins" and "Clinical manifestations and diagnosis of vitamin B12 and folate deficiency", section on 'Neuropsychiatric changes')

Lyme disease (see "Nervous system Lyme disease", section on 'Peripheral neuropathy')

However, some important exceptions exist. As an example, polyneuropathy associated with monoclonal gammopathies can sometimes be demyelinating. (See "Immune-mediated neuropathies", section on 'Monoclonal gammopathy of undetermined significance'.)

Autoimmune — Most acute autoimmune neuropathies, namely Guillain-Barré syndrome, are predominantly demyelinating, and a variety of clinical and experimental data have implicated both humoral factors and cell-mediated immune phenomena, which damage myelin and/or the myelin-producing Schwann cells. (See "Guillain-Barré syndrome in adults: Pathogenesis, clinical features, and diagnosis".)

However, axonal forms of this disease also exist. For example, one unusual but well-described variant of Guillain-Barré syndrome is that of acute motor axonal polyneuropathy (AMAN). In this disorder, primary invasion of axons by inflammatory cells has been described [2]. (See "Guillain-Barré syndrome in adults: Pathogenesis, clinical features, and diagnosis" and "Guillain-Barré syndrome in children: Epidemiology, clinical features, and diagnosis".)

Toxic — Many toxic neuropathies, such as those due to alcohol, chemotherapy exposure, and most heavy metals, produce a predominantly axonal disorder that can be acute, subacute, or chronic, depending on the level and severity of the exposure. Nonetheless, it is incorrect to simply classify all toxic neuropathies as axonal, since many exceptions exist [3]. As an example, n-hexane exposure leads to neuropathy that has a substantial demyelinating component [4].

Aside from chemotherapeutic drugs, a variety of commonly used medications have been implicated in toxic neuropathies (table 1B). Examples include antimicrobials (eg, dapsone, fluoroquinolones, isoniazid, metronidazole, nitrofurantoin), antiretrovirals (eg, stavudine), amiodarone, colchicine, disulfiram, phenytoin, pyridoxine, tumor necrosis factor inhibitors (eg, infliximab), and immune checkpoint inhibitors (eg, ipilimumab). In many cases, the magnitude of risk is relatively low, and recognition of the adverse effect may require a high index of suspicion, especially for commonly used drugs such as fluoroquinolones. (See "Prevention and treatment of chemotherapy-induced peripheral neuropathy", section on 'Chronic neurotoxicity' and "Tumor necrosis factor-alpha inhibitors: An overview of adverse effects", section on 'Demyelinating disease' and "Fluoroquinolones", section on 'Neurologic' and "Toxicities associated with checkpoint inhibitor immunotherapy", section on 'Neurologic' and "Epidemiology, clinical manifestations, diagnosis, and treatment of HIV-associated distal symmetric polyneuropathy (HIV-DSPN)", section on 'Risk factors'.)

Hereditary — The most common forms of hereditary neuropathy (table 1C), namely CMT types 1A, 1B, and X-linked, are all predominantly demyelinating in nature, although substantial coexistent axonal loss is usually also identified. (See "Charcot-Marie-Tooth disease: Genetics, clinical features, and diagnosis".)

Other rare hereditary diseases that cause predominantly demyelinating polyneuropathies include those secondary to metabolic diseases of childhood, such as Krabbe disease, metachromatic leukodystrophy, adrenoleukodystrophy, and mitochondrial disorders.

Peripheral neuropathies associated with mitochondrial disorders most often exhibit an axonal pattern, as occurs with CMT type 2A and the syndrome of neuropathy, ataxia, and retinitis pigmentosa (NARP) [5]. Other mitochondrial disorders are associated with a demyelinating neuropathy, as occurs with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE).

Porphyric neuropathy is primarily an axonal motor neuropathy that usually presents in the context of acute neurovisceral attacks, with variable manifestations of neuropathy, abdominal pain, confusion, and other neurologic and systemic symptoms. The acute hepatic porphyrias are inherited disorders caused by partial enzyme deficiencies affecting heme biosynthesis. Neurovisceral attacks are manifestations of four types of hepatic porphyria. The most common of these is acute intermittent porphyria; the others are hereditary coproporphyria, variegate porphyria, and delta-aminolevulinic acid dehydratase porphyria. (See "Acute intermittent porphyria: Pathogenesis, clinical features, and diagnosis" and "Hereditary coproporphyria" and "Variegate porphyria" and "ALA dehydratase porphyria".)

Environmental — Environmental factors can also impact nerve health in substantial ways. Neuropathies associated with vibration-induced nerve damage, prolonged cold exposure, or hypoxemia [6] have been well described. These disorders are mainly axonal in nature.

Idiopathic — Although population-based data are lacking, no specific cause is identified in up to 46 percent of patients with polyneuropathy at referral centers despite extensive investigations [7-11]. A variety of terms have been employed to describe this disorder, including chronic idiopathic axonal polyneuropathy (CIAP), chronic sensory polyneuropathy, chronic polyneuropathy of undetermined cause, unclassified peripheral neuropathy, and idiopathic neuropathy. Most such cases present in adults ≥50 years of age and progress slowly over months to years. The symptoms are typically sensory, involving paresthesia, numbness, or pain. Electrodiagnostic studies show a primarily axonal polyneuropathy. Proposed but unproven causes include impaired glucose tolerance, hypertension, dyslipidemia, and increased oxidative stress [8].

CLINICAL PRESENTATION — Polyneuropathy is typically characterized by symmetric distal sensory loss, burning sensations, or weakness. Patients with very mild or asymptomatic polyneuropathy occasionally are identified on detailed sensory examination of the lower extremities. Alternatively, a patient may undergo electrodiagnostic testing for an unrelated problem, such as carpal tunnel syndrome, and mild abnormalities suggestive of polyneuropathy are identified. More advanced cases, however, typically present with symptoms suggestive of peripheral nerve disease, which may or may not be supported by findings on physical examination (table 2A-C).

History — The presentation of patients with polyneuropathy varies significantly depending upon the underlying pathophysiology.

Chronic axonal polyneuropathies (eg, due to diabetes mellitus or uremia) are the most common of the polyneuropathies. Injury tends to be related to axon length; thus, longer axons are affected first, resulting in symptoms that begin in the lower extremities. Sensory symptoms usually precede motor symptoms. Patients typically present with slowly progressive sensory loss and dysesthesias such as numbness, a burning sensation and pain in the feet, and mild gait abnormalities. As the syndrome progresses, mild weakness of the lower legs and hand symptoms may begin, resulting in the classic "stocking and glove" distribution of sensory loss. The numbness may continue to extend proximally in severe cases, affecting the intercostal nerves (the next longest nerve fibers after the arms) and causing sensory loss over the sternum. The top of the head may be affected with further progression.

In acute axonal polyneuropathies, such as that produced by toxic exposures or porphyria, patients may present with similar but much more fulminant symptoms. Pain is often a predominant component, although it can be distinctly absent. The polyneuropathy tends to worsen over two to three weeks, plateau, and then recover over months. Although often dose related, some toxic neuropathies can occur within days of drug exposure and appear to be idiosyncratic, as in fluoroquinolone-associated neuropathy. (See "Fluoroquinolones", section on 'Neurologic'.)

In patients with acute demyelinating polyneuropathies, primarily Guillain-Barré syndrome, the presentation is often quite distinct from that of most axonal polyneuropathies. Guillain-Barré syndrome tends to affect predominantly motor nerve fibers; thus, weakness rather than sensory loss typically is one of the earliest signs of the disease. Eventually, however, most patients will complain of some dysesthesias distally in the legs or arms. Gait difficulties or hand clumsiness secondary to reduced proprioception are also common complaints.

Weakness and generalized sensory loss are often present simultaneously in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). (See "Chronic inflammatory demyelinating polyneuropathy: Etiology, clinical features, and diagnosis".)

Patients with hereditary polyneuropathies generally do not complain of positive symptoms such as paresthesias or pain. Often neither patients nor their families appreciate marked neurologic deficits or atrophy since the progression of the disease is slow and insidious [12].

The history is important for distinguishing between polyneuropathy and mononeuropathy multiplex. Occasionally patients with the former will have symptoms that begin in one foot shortly before the other or are more pronounced in one foot. Mononeuropathy multiplex, in its acute form, usually presents with multiple mononeuropathies with involvement of entirely unrelated nerves, such as the median nerve in the arm and the sciatic nerve in the leg. However, patients may occasionally present with more symmetric sensory and motor symptoms affecting both legs that can be difficult to differentiate on clinical grounds from a severe subacute polyneuropathy. On detailed examination, relative preservation of one nerve (eg, posterior tibial) compared with another (eg, peroneal) may be identified.

Physical examination — Abnormalities on physical examination are similarly dependent upon the type of polyneuropathy (axonal versus demyelinating) and which classes of nerve fibers are most involved (motor versus sensory).

In patients with an axonal polyneuropathy, motor examination may disclose wasting of the intrinsic muscles of the feet or lower leg; similar findings are evident in the hands in more severe cases. Distal loss of sensation to pin prick, light touch, vibration, cold, and proprioception may also occur. Reflexes become hypoactive or absent distally, usually at the ankles initially.

By contrast, generalized weakness is the rule in patients with symptoms of a more fulminant polyneuropathy secondary to demyelination. Distal muscles are predominantly affected, although weakness may affect proximal muscles to a greater extent in some individuals. Sensation is also reduced; large myelinated fibers are most damaged, resulting in abnormalities of vibratory testing and proprioception that are often out of proportion to loss of pin prick or temperature sensation. Reflexes are reduced diffusely and are often absent.

Causes of painful sensory polyneuropathy include the following (table 3):

Idiopathic small fiber neuropathy

Diabetic peripheral neuropathy

Neuropathy related to connective tissue disease

Vasculitic neuropathy

Neuropathy associated with monoclonal gammopathy

Paraneoplastic sensory neuropathy

Familial or acquired amyloid polyneuropathy

Certain toxic neuropathies

Clinical course — Patients with chronic axonal polyneuropathies generally experience a slow progression of disease over a period of years. As examples, in patients with diabetic polyneuropathy or older adults with an idiopathic axonal polyneuropathy, sensory loss will slowly ascend and increase in severity in the legs before the hands become affected (see "Screening for diabetic polyneuropathy"). In patients with axonal polyneuropathy secondary to toxins, such as alcoholic polyneuropathy, exacerbations will follow increasing exposure to the pathogen. When a one-time event has occurred, such as axonal polyneuropathy secondary to critical illness, gradual but incomplete recovery in distal sensation and strength is the rule, often over a period of many months or years. (See "Neuromuscular weakness related to critical illness".)

The course of inflammatory demyelinating polyneuropathy is extremely variable. In patients with Guillain-Barré syndrome, a two- to six-week period of decline is followed by stabilization and eventual improvement over several months; recovery generally depends upon the initial illness severity. (See "Guillain-Barré syndrome in adults: Treatment and prognosis" and "Guillain-Barré syndrome in children: Epidemiology, clinical features, and diagnosis".)

In patients with CIDP, exacerbations may be followed by periods of stability in some, while in others there is a steady prolonged decline. (See "Chronic inflammatory demyelinating polyneuropathy: Etiology, clinical features, and diagnosis" and "Chronic inflammatory demyelinating polyneuropathy: Treatment and prognosis".)

Patients with congenital demyelinating polyneuropathy, such as Charcot-Marie-Tooth (CMT) disease, also have a variable course, even between related family members with the disease. Some patients may first present in childhood, while others not until they are well into the seventh or eighth decade of life. After presentation, however, a very slow but inevitable progression of symptoms will occur. (See "Charcot-Marie-Tooth disease: Genetics, clinical features, and diagnosis".)

DIFFERENTIAL DIAGNOSIS — Diseases of the central nervous system can be difficult to distinguish from polyneuropathy. As an example, progressive numbness and weakness in the lower extremities may be due to a spinal cord process or polyneuropathy. Furthermore, acute myopathy, neuromuscular junction disease, or a central process may mimic Guillain-Barré syndrome or chronic inflammatory demyelinating polyneuropathy (CIDP). (See "Differential diagnosis of peripheral nerve and muscle disease".)

DIAGNOSTIC EVALUATION — There are a number of issues to consider when evaluating patients who present with symptoms consistent with polyneuropathy [1,12-15]. Extensive diagnostic testing is probably not necessary in a patient with mild symptoms who has a known underlying reason (eg, diabetes mellitus, alcohol abuse, or chemotherapy). On the other hand, a diagnostic evaluation is warranted in patients with no clear etiology or in whom symptoms are severe or rapidly progressive, and for patients with atypical features. (See 'Features warranting a full evaluation' below.)

In addition to the history of the neuropathy itself, the patient should be asked about recent viral illnesses; other systemic symptoms; new medications; exposures to solvents, heavy metals, or other potential toxins; alcohol use; and a family history of neurologic disease.

Features warranting a full evaluation — A full diagnostic evaluation should be pursued in patients with atypical features, including [14]:

Asymmetry

Non-length dependence

Motor predominance

Acute onset

Prominent autonomic involvement

Severe or rapidly progressive symptoms

Sensory ataxia

Diagnosis of polyneuropathy — A case definition of distal symmetric polyneuropathy developed by an expert panel may aid clinicians by providing diagnostic criteria with a relatively high sensitivity and specificity [16]. The panel assessed the diagnostic accuracy of neuropathic symptoms, neurologic signs (decreased or absent ankle reflexes, decreased distal sensation, distal muscle weakness or atrophy), and nerve conduction study (NCS) findings based on evidence from 12 high-quality studies. Diabetic peripheral neuropathy was the focus of most of these studies. The following observations were noted [16]:

Symptoms alone have a relatively poor diagnostic accuracy. Multiple neuropathic symptoms are more accurate than single symptoms.

Signs are better predictors of polyneuropathy than symptoms and should be weighted more heavily. A single abnormality on examination is less sensitive than multiple abnormalities. Therefore, an examination for polyneuropathy should look for a combination of signs.

Abnormal electrodiagnostic studies provide a higher level of specificity to the case definition, but they should not be used alone to make the diagnosis. Abnormal NCS are the most informative part of the electrodiagnostic evaluation.

A set of case definitions was rank ordered by estimated likelihood of distal symmetric polyneuropathy (table 4) [16]. The highest likelihood of polyneuropathy occurred when a combination of multiple symptoms and signs was accompanied by abnormal electrodiagnostic studies. A modest likelihood of polyneuropathy occurred when a combination of multiple symptoms and signs was present but electrodiagnostic studies were not available. A lower likelihood of polyneuropathy occurred when electrodiagnostic studies and signs were discordant.

Electrodiagnostic testing — We suggest electrodiagnostic testing with electromyography (EMG) and/or NCS as the initial diagnostic procedure for patients with suspected polyneuropathy (algorithm 1) when there is no clear etiology, when symptoms are severe or rapidly progressive, or when atypical features are present, including asymmetry, non-length dependence, motor predominance, acute onset, or prominent autonomic involvement. (See 'Features warranting a full evaluation' above and "Overview of electromyography".)

Electrodiagnostic studies can determine if the disorder is due to a primary nerve (neuropathy) or muscle disorder (myopathy). These tests also can identify whether the patient's symptoms are secondary to a polyneuropathy or another peripheral nerve disorder (eg, polyradiculopathy from lumbar stenosis); if it is a polyneuropathy, EMG/NCS will reveal whether it is axonal or demyelinating in character. The clinical examination alone generally cannot make the latter distinction.

Electrodiagnostic features of demyelinating disorders include:

Slow nerve conduction velocity

Dispersion of evoked compound action potentials

Conduction block (decreased amplitude of muscle compound action potentials on proximal compared with distal nerve stimulation)

Marked prolongation of distal latencies

By contrast, axonal neuropathies are characterized by a reduced amplitude of evoked compound action potentials with relative preservation of the nerve conduction velocity.

IDENTIFYING THE ETIOLOGY — We recommend selective use of laboratory tests in patients with polyneuropathy, based upon the history and the results of electrodiagnostic tests (table 5). In practice, this means that most blood tests should be deferred until the results of electromyography (EMG) and nerve conduction study (NCS) testing are known.

One clear distinction that can be made by clinical neurophysiology is whether a neuropathy is due to axon loss or demyelination. As an example, thyroid function studies are unlikely to be useful if the neuropathy has prominent demyelinating features. Thus, instead of obtaining a laboratory "screen" for neuropathy, specific tests should be ordered based upon the pathophysiology of the underlying process (table 5). This approach is more cost effective and less confusing than ordering multiple unneeded diagnostic tests.

In patients with distal symmetric polyneuropathy who are not initially evaluated with NCS, the laboratory tests with the highest yield for detecting abnormalities are blood glucose, serum B12 level with methylmalonic acid (with or without homocysteine), and serum protein electrophoresis (SPEP) (table 5) [17]. This observation does not imply, however, that this screening approach is superior to choosing appropriate blood tests after clinical neurophysiologic evaluation has been performed.

Additional testing for select patients may include lumbar puncture, genetic testing, and muscle or nerve biopsy.

EMG with axonal physiology — An EMG study showing a predominantly axonal neuropathy suggests that the etiology is a systemic disorder, toxin, or drug. The initial laboratory evaluation should include blood glucose, glycohemoglobin, serum B12 level, SPEP and immunofixation, urine protein electrophoresis (UPEP) and immunofixation, thyroid stimulating hormone (TSH), and serum antinuclear antibodies (ANA). The personal and family history should be scrutinized for any evidence suggesting hereditary neuropathies that are axonal in nature, including Charcot-Marie-Tooth (CMT) type 2, mitochondrial disorders, and porphyria. If the initial testing is unrevealing, it is reasonable to test for urine heavy metals, urine porphyrins, and rheumatoid factor, to obtain methylmalonic acid and homocysteine levels for patients with borderline levels of serum B12, and to evaluate for Sjögren disease, Lyme disease, HIV infection, and hepatitis B and C. In the presence of sensory neuronopathy, anti-Hu (ANNA-1) antibody testing is warranted.

EMG with demyelinating physiology — An EMG study showing a predominantly demyelinating physiology suggests that the etiology is an autoimmune condition or a hereditary disorder. The personal and family history should be evaluated for any evidence suggesting hereditary neuropathies that are demyelinating in nature. In the presence of a compatible family history, examination, and/or hereditary features on EMG, genetic evaluation for CMT types 1A, 1B, and X-linked is warranted. Hereditary features include a fairly homogeneous slowing of conduction across all nerves without conduction block; acquired features generally have more heterogeneous slowing and conduction block, though the rule does not always hold (eg, in X-linked CMT disease).

If the evaluation points towards an acquired demyelinating polyneuropathy, then testing to detect monoclonal proteins is advised with SPEP and immunofixation, and UPEP and immunofixation. In addition, GM1 antibody testing and lumbar puncture for cerebrospinal fluid analysis is advised. HIV, hepatitis B, and hepatitis C testing is indicated for patients at increased risk for these conditions and for those with liver dysfunction or cerebrospinal fluid pleocytosis. Anti-MAG antibodies are indicated in the setting of immunoglobulin M (IgM) monoclonal paraprotein when distal latencies are prolonged out of proportion to conduction velocities. A lumbar puncture is helpful because most inflammatory demyelinating polyneuropathies have a radicular component that produces a marked increase in spinal fluid protein with minimal elevation in cerebrospinal fluid white cells (albuminocytologic dissociation).

EMG with mixed axonal and demyelinating physiology — With an EMG study showing a mixed axonal and demyelinating physiology, the workup is the same as with a demyelinating physiology (see 'EMG with demyelinating physiology' above). If that workup is nondiagnostic, it is reasonable to evaluate for causes of an axonal physiology (see 'EMG with axonal physiology' above) and/or pursue a peripheral nerve biopsy.

EMG with polyradiculopathy, plexopathy, or mononeuropathy multiplex — For patients with EMG evidence of polyradiculopathy or plexopathy, the workup should include neuroimaging studies of the affected regions of the spine and brachial or lumbosacral plexus. (See "Polyradiculopathy: Spinal stenosis, infectious, carcinomatous, and inflammatory nerve root syndromes" and "Brachial plexus syndromes" and "Lumbosacral plexus syndromes".)

For patients with EMG evidence of mononeuropathy multiplex, serologic studies (eg, antineutrophil cytoplasmic antibodies [ANCA], cryoglobulins, tests for HIV and hepatitis B and hepatitis C virus infections, and other labs) and nerve biopsy may aid identification of the underlying cause, which is typically a vasculitis. (See "Clinical manifestations and diagnosis of vasculitic neuropathies" and "Treatment and prognosis of nonsystemic vasculitic neuropathy".)

Normal EMG — Patients with suspected polyneuropathy who have a normal EMG study should be observed for any progression of symptoms. EMG studies can be repeated if there is clinical progression. Additional workup for possible small fiber neuropathy includes skin biopsy and autonomic testing. (See 'Skin biopsy' below and 'Autonomic testing' below.)

Nerve biopsy — Nerve biopsy is rarely useful for diagnosing the underlying etiology of polyneuropathy. Nerve biopsy generally is reserved for patients in whom vasculitis or amyloidosis is suspected. Identifying demyelination with associated inflammation in these individuals may help guide treatment. (See 'Management' below.)

Pathologic study of nerve is sometimes helpful for picking up infiltrative diseases such as amyloid neuropathy, infectious diseases such as leprosy, mononeuropathy multiplex due to vasculitis, and sarcoidosis [18,19]. Clinically, all of these entities are characterized by some degree of asymmetry or focality.

Nerve biopsy is of low yield and should generally be avoided in patients with subacute or chronic distal symmetric polyneuropathies. The literature pertaining to this issue is sparse [20].

The sural nerve at the distal calf is the preferred site for cutaneous nerve biopsy. Simultaneous biopsy of the superficial peroneal nerve and peroneus brevis muscle with a single incision increases the yield for the diagnosis of vasculitic neuropathy [21-23]. Rarely, other nerves including the superficial radial, saphenous, or intermediate cutaneous nerve of the thigh can be biopsied.

Skin biopsy — Epidermal skin biopsy is an especially useful test in the diagnosis of polyneuropathy that predominantly affects small, unmyelinated nerve fibers [24-26]. Typical symptoms of small fiber neuropathy are distal burning, pain, numbness, and paresthesias.

Standard electrophysiologic testing is often normal in disorders affecting mainly small, unmyelinated nerve fibers, and sural nerve biopsy may be normal or only minimally abnormal.

The test is performed by removing a very small piece of skin just proximal to the ankle; the wound is allowed to heal by secondary intention. Special stains are then applied to the skin tissue and the number and morphology of axons within the epidermis evaluated, either by qualitative assessment or by careful counting to determine intraepidermal nerve fiber density [27]. These values are compared with age-dependent normal values [28].

A systematic review and practice parameter published in 2009 by the American Academy of Neurology (AAN), the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM), and the American Academy of Physical Medicine and Rehabilitation (AAPM&R) concluded that intraepidermal nerve fiber density determination, using antiprotein gene product 9.5 immunohistochemistry, is a validated and reproducible marker of small fiber sensory neuropathy [20].

Given the relative simplicity of the technique and its ability to provide quantitative data, the test is also likely to be useful in following disease progression or response to treatment.

Autonomic testing — Autonomic testing can be informative for evaluating patients with small fiber sensory neuropathy [20]. The composite autonomic scoring scale (CASS), which includes measurements of orthostatic blood pressure, the quantitative sudomotor axon reflex test, heart rate response to tilt, heart rate variability with deep breathing, and changes in blood pressure with the Valsalva maneuver, appears to provide a useful measure of autonomic function and can help support a diagnosis of small fiber sensory neuropathy [20]. The evaluation of intraepidermal sweat glands is a viable technique to evaluate sudomotor function [29].

Quantitative sensory testing — Quantitative sensory testing measures the degree of sensory loss to various modalities, including temperature and vibration. It is helpful in some patients to identify subtle abnormalities and demonstrate the progression or stability of disease.

MANAGEMENT — There are two separate aspects to the treatment of polyneuropathy: treatment of the underlying disease and alleviation of symptoms related to the illness.

Treatment of the underlying process — Disease-specific treatment of polyneuropathy obviously depends upon the underlying process. Nevertheless, some generalizations can be made for treating the axonal and demyelinating polyneuropathies.

Axonal polyneuropathies — Reducing exposure to endogenous or exogenous toxins that may be causing the polyneuropathy is the single most important step in treating and preventing the progression of axonal polyneuropathies. As an example, in patients with axonal polyneuropathy secondary to alcohol or drugs, avoidance of the offending agent is extremely important.

In patients with diabetes mellitus, tight control of blood glucose may help maintain nerve function. (See "Management of diabetic neuropathy", section on 'Glycemic control'.)

Similarly, in patients with a polyneuropathy secondary to one of the rheumatic diseases, treatment of the underlying illness is important to at least halt the progression, if not to reverse symptoms. Thyroid replacement typically ameliorates the symptoms of hypothyroid polyneuropathy. (See "Neurologic manifestations of hypothyroidism", section on 'Peripheral neuropathy'.)

Demyelinating polyneuropathies — Unlike axonal polyneuropathy, many treatment options are available for most acquired demyelinating polyneuropathies, such as chronic inflammatory demyelinating polyneuropathy (CIDP) or Guillain-Barré syndrome. (See "Chronic inflammatory demyelinating polyneuropathy: Treatment and prognosis" and "Guillain-Barré syndrome in adults: Treatment and prognosis".)

Treatment of the underlying disease is most important in patients with CIDP secondary to a lymphoproliferative disorder such as multiple myeloma or Waldenström macroglobulinemia. The mainstays of treatment for CIDP are intravenous immune globulin, glucocorticoids, and plasma exchange. These treatments appear to be equally effective. (See "Chronic inflammatory demyelinating polyneuropathy: Treatment and prognosis".)

Some disorders respond better than others; patients with immunoglobulin G (IgG) and IgA monoclonal gammopathies of undetermined significance tend to respond better than patients with IgM [30].

Treatment of symptoms and prevention of complications — Gabapentin may reduce pain associated with polyneuropathy and is generally well tolerated. Tricyclic antidepressants have been utilized for many years for this condition and are generally considered effective.

The management of pain associated with diabetic neuropathy and vasculitic neuropathy is discussed in separate topic reviews. (See "Management of diabetic neuropathy", section on 'Pain management' and "Treatment and prognosis of nonsystemic vasculitic neuropathy".)

Many other medications have also been tried in the treatment of painful polyneuropathy with varying success, including duloxetine, pregabalin, carbamazepine, phenytoin, topiramate, baclofen, mexiletine, and dextromethorphan. Unfortunately, there are no well-executed studies comparing the effectiveness of these drugs for this condition, thereby limiting the ability of practitioners to make evidence-based decisions.

Simultaneous treatment with drugs such as tramadol, nonsteroidal anti-inflammatory drugs (NSAIDs), or low-dose narcotics may be necessary in some patients for occasional "breakthrough pain."

Physical therapy evaluation is important in patients with significant weakness. Appropriate use of ankle-foot orthoses, splints, and walking assistance devices can significantly improve lifestyle in the face of significant disability.

Patients with distal polyneuropathy are at increased risk for developing foot ulcers; proper foot and nail care is especially important in this population. Regular visits to a podiatrist can also help prevent problems. (See "Evaluation of the diabetic foot".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Neuropathy".)

SUMMARY AND RECOMMENDATIONS

Etiology and pathogenesis – The peripheral nerves are susceptible to a variety of toxic, inflammatory, hereditary, infectious, and parainfectious factors that can impair their health and function, leading to the clinical disorder of polyneuropathy. Polyneuropathy has a wide variety of causes, ranging from the common, such as diabetes mellitus, alcohol abuse, and HIV infection, to the rare. It may occur as a manifestation of systemic disease, a side effect of medication, or genetic process, but many cases are idiopathic (table 1A-C). (See 'Etiology and pathogenesis' above.)

Clinical presentation – Polyneuropathy is typically characterized by symmetric distal sensory loss, burning, or weakness. The presentation of patients with polyneuropathy varies significantly depending upon the underlying pathophysiology. Abnormalities on physical examination are similarly dependent upon the type of polyneuropathy (axonal versus demyelinating) and which classes of nerve fibers are most involved (motor versus sensory). (See 'Clinical presentation' above.)

Differential diagnosis – Several conditions of the central nervous system can be difficult to distinguish from polyneuropathy. These include spinal cord processes, acute myopathies, and neuromuscular junction disease. (See "Differential diagnosis of peripheral nerve and muscle disease".)

Diagnostic evaluation – The likelihood of an accurate diagnosis of polyneuropathy is highest when a combination of multiple symptoms and signs is accompanied by abnormal electrodiagnostic studies (table 4). Extensive testing is unnecessary in a patient with mild symptoms who has a known underlying reason (eg, diabetes mellitus, alcohol abuse, or chemotherapy). On the other hand, a diagnostic evaluation is warranted in patients with no clear etiology or in whom symptoms are severe or rapidly progressive and for patients with atypical features.

Electrodiagnostic studies – Electromyography/nerve conduction studies should be the initial diagnostic study in all patients with symptoms and signs of polyneuropathy (algorithm 1). (See 'Diagnostic evaluation' above.)

Laboratory testing – We recommend selective use of laboratory tests in patients with polyneuropathy, based upon the history, clinical features, and results of electrodiagnostic tests (algorithm 1 and table 5). (See 'Identifying the etiology' above.)

Other testing – Specialized testing such as lumbar puncture, genetic testing, nerve biopsy, skin biopsy, and autonomic testing is reserved for selected patients with specific features when the underlying cause is not identified on initial evaluation. (See 'Diagnostic evaluation' above.)

Management – There are two separate aspects to the treatment of polyneuropathy: treatment of the underlying disease and alleviation of symptoms related to the illness. (See 'Management' above.)

Treatment of the underlying illness is important to at least halt the progression and, in some cases, to reverse symptoms. In addition, immunomodulatory treatments are available for most acquired demyelinating polyneuropathies, such as chronic inflammatory demyelinating polyneuropathy or Guillain-Barré syndrome. (See 'Treatment of the underlying process' above.)

Many medications for symptomatic management have been used with varying success. Gabapentin and tricyclic antidepressants are generally considered effective and may reduce pain associated with polyneuropathy. (See 'Treatment of symptoms and prevention of complications' above.)

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