Polyneuropathy: Everything You Need to Know

Polyneuropathy is a type of neuropathy, or nerve disease, that affects many nerves. In general, polyneuropathy is caused by a systemic disease process (affecting the whole body) that damages many nerves, like diabetes or chronic alcohol overuse.

The types of conditions that cause polyneuropathy often harm peripheral nerves throughout the body, causing symptoms such as pain, decreased sensation, and weakness. Treatments can include medication to prevent nerve damage, physical therapy, and pain medications.

Depending on how soon it is diagnosed and treated, the nerve damage of polyneuropathy can often be slowed down with treatment. This article will explore the types of polyneuropathy, causes, associated conditions, risk factors, symptoms, diagnosis, and treatment.

Polyneuropathy Types

Polyneuropathies are either acute or chronic. Acute polyneuropathies develop over the course of days or weeks and can cause serious health risks. Chronic polyneuropathies might not always cause noticeable symptoms at first, but they can be distressing and irreversible when they finally are experienced.

They can be described as:

• Acute polyneuropathies involve sensory and motor symptoms, which can develop at nearly the same time and progress rapidly. 
• Chronic polyneuropathies develop slowly, often causing discomfort before they cause sensory loss or weakness. 

Polyneuropathy Causes

Polyneuropathy affects the peripheral nerves, which are the nerves that control the movement of the arms and legs. It occurs due to peripheral nerve damage or demyelination—damage to the myelin sheath—of the peripheral nerves. Myelin is a fatty covering that helps insulate nerves, allowing them to function efficiently.

Sometimes, demyelination can be reversible because the body naturally regenerates myelin. Nerve damage is not reversible because nerves do not heal. Generally, peripheral nerve demyelination occurs before nerve damage, but this is not always the case.  

The different causes of polyneuropathy include:

Diabetic neuropathy: High blood glucose can cause changes in the body that lead to nerve damage, potentially affecting the nerves in the distal (farthest from the center of the body) extremities and nerves of the gastrointestinal system.

Alcohol-induced neuropathy: Alcohol can cause significant damage throughout the body, including liver disease. Metabolic changes and toxicity caused by chronic alcohol overuse can harm the peripheral nerves. 

Neuropathy of chronic illness: Many people who have serious illnesses, like heart disease, kidney disease, gastrointestinal disease, or lung disease, may develop polyneuropathy that progresses slowly. Factors like nutritional deficiencies, chronic oxygen deprivation, and taking multiple medications can all contribute to this.

ICU neuropathy: Also called critical illness neuropathy, this condition can develop rapidly. It is associated with several contributing factors, including malnutrition, inflammation, metabolic abnormalities, infections, and medication toxicity.

Metabolic neuropathy: Metabolic changes, such as low or high sodium, potassium, magnesium, or calcium levels, may affect the way the nerves function, leading to symptoms of polyneuropathy.

Medication: Some medications, especially chemotherapy, are associated with this side effect. Some medications directly attack the nerves, and some may cause nutritional or metabolic effects that lead to nerve damage.

Cancer: Cancer may cause polyneuropathy in several different ways. It can directly infiltrate the nerves and the surrounding areas. Additionally, paraneoplastic syndromes are a rare type of nervous system disease that's caused by cancer. They occur when cancer causes the development of antibodies (a type of immune protein) to attack the nerves.

One such paraneoplastic syndrome is called polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS syndrome).

Thyroid disease: Both hypothyroidism (low thyroid hormone function) and hyperthyroidism (excessive thyroid hormone function) have been associated with polyneuropathy.

Inflammatory: Inflammation that may damage nerves can occur in association with medical conditions, such as diabetes. And inflammation can also occur in response to infections or without another identifiable cause.

Autoimmune: Autoimmune disease, such as systemic lupus erythematosus (SLE), may be associated with an increased likelihood of polyneuropathy.

Infections: Sometimes viral infections, including human immunodeficiency virus (HIV) infection, can cause polyneuropathy.

Guillain-Barre syndrome (GBS): Also known as acute inflammatory demyelinating polyneuropathy, GBS is a rapidly developing disease that causes demyelination of the nerves of the lower extremities, followed by involvement of the upper legs, arms, trunk, and respiratory muscles.

People who have GBS need intensive medical care, which includes immune suppression therapy and possibly respiratory support. Miller Fisher syndrome is a subtype of GBS.

Chronic inflammatory demyelinating polyneuropathy (CIDP): This condition is similar to GBS, but it is recurrent and chronic. The weakness of CIDP is not usually as severe as the weakness of GBS. Treatment can involve immune suppression therapy.

Compressive: Sometimes physical pressure can cause damage to multiple nerves. This may occur as a result of things like spine disease or inflammation.

Symptoms

The symptoms of polyneuropathy affect more than one limb (arm or leg). Generally, distal nerves, which are located in the fingers, toes, hands, and feet, are involved more severely than proximal nerves of the upper arms and thighs. The effects are usually almost symmetrical. 

The symptoms also can involve nerves in the face. Sometimes, physical functions, digesting food and breathing, can be affected as well. 

Symptoms of polyneuropathy can include:

• Numbness, tingling, pain, or burning of the fingers, hands, toes, or feet
• Decreased sensation of the distal extremities, sometimes with unawareness of injuries
• Weakness and lack of coordination of distal extremities, sometimes with a tendency to become injured 
• Trouble walking, which can cause falling 
• Diarrhea or constipation 
• Trouble breathing 
• Urinary incontinence or retention (unable to urinate when you want to) 

You can have one or more of these symptoms if you have polyneuropathy. Rarely, heart function can also be affected by systemic polyneuropathy.

Risk Factors

Certain underlying conditions are known to cause polyneuropathy. Uncontrolled diabetes and chronic alcohol overuse are the most common. Sometimes people who have well-controlled diabetes are at increased risk as well. 

Some chemotherapeutics and other medications are known to cause this side effect. And living with inflammatory or autoimmune diseases can increase the risk as well. 

Nutritional causes of polyneuropathy can be more likely in people who do not get enough nutrients in the diet. Additionally, malabsorption issues due to digestive diseases or intestinal or stomach surgery can interfere with proper nutrient absorption. 

Diagnosis

The diagnosis of polyneuropathy involves a medical history, physical examination, sometimes electrical nerve tests or blood tests, and, rarely, a biopsy. 

The key feature of a physical examination include diminished reflexes, which generally affect nerves farther from the center of the body. Decreased sensation is often also detected.

During the sensory portion of your physical examination, you can expect your healthcare provider to examine your ability to feel pain, light touch, position changes, temperature, and vibration. With polyneuropathy, one or more of these sensations is usually diminished in the fingers and toes. It may improve as the testing moves up the arms or legs.

You may also be slightly weak and have trouble walking. Sometimes, with chronic polyneuropathy, muscle tone is decreased, resulting in floppiness, and the muscles can be atrophied (shrunk) as well. 

Diagnostic tests may include:

• Complete blood count (CBC) test to check for signs of inflammation or infection
• Blood tests to look for specific antibodies or inflammatory markers
• Glucose level or glycosylated hemoglobin to check for diabetes or uncontrolled diabetes 
• Liver function tests to check for signs of alcoholic liver disease 
• Imaging tests to identify nerve compression 
• Nerve conduction studies (NCS) and electromyography (EMG) to check nerve and muscle function
• Nerve or muscle biopsy (removal of tissue to analyze in the lab) to identify unusual patterns of disease 

The additional tests you might need would be guided by your symptom history and physical examination. 

Treatment

There are treatments for some of the discomfort and painful symptoms of polyneuropathy. Additionally, medical interventions can sometimes help prevent the condition from progressing. Most people who have polyneuropathy would benefit from exercise and physical therapy:

• Treatments for pain and discomfort can include anti-epilepsy drugs (AEDs), like Neurontin (gabapentin) or antidepressants. 
• Treatments to prevent progression can include strategies to control the underlying cause, such as blood sugar control for diabetes, anti-inflammatory medications for autoimmune and inflammatory disease, and nutritional supplementation for nutritional deficits.
• If the respiratory muscles are affected, as with GBS, respiratory support with mechanical ventilation may be necessary. 

Often, physical therapy and exercises can help alleviate discomfort. This is also important to avoid atrophy and to maximize strength as much as possible.

Outlook

Generally, the nerve damage of polyneuropathy does not heal. Sometimes, demyelination can heal. For example, the effects of GBS will often partially or fully resolve because the condition is caused by demyelination. 

Managing complications can improve overall health and outcome. This can include checking the extremities for visible signs of wounds or injuries on a daily basis and making sure that all wounds are clean and properly taken care of to prevent an infection. 

Summary 

Polyneuropathy is a medical condition that affects nerves throughout the body. This typically occurs due to a systemic (whole-body) illness like diabetes or alcohol-related disease. There are many causes of polyneuropathy, and diagnosis of the cause is important for preventing the progression of the nerve damage.

Polyneuropathy can cause pain, diminished sensation, and weakness. Treatments can alleviate discomfort but cannot repair sensory loss of weakness. Physical therapy and medical interventions can help maximize abilities and prevent complications.