Polyneuropathy

Nerves located outside of the spinal cord and brain are known as peripheral nerves. These have many different functions. For example, they control muscle movement and transmit stimuli such as touch, heat or pressure to the brain.

Conditions caused by damage to these nerves are referred to as polyneuropathy or peripheral neuropathy.

The causes may be very varied and are not always known. Nerve damage is often caused by poorly managed diabetes (diabetic neuropathy) or heavy alcohol consumption (alcoholic neuropathy).

Pain and prickling sensations called paresthesia – particularly in the feet – are common symptoms. Muscle weakness and an unsteady gait may also be indicators of polyneuropathy.

Treatment aims to identify and eliminate the cause as far as possible.

There is a wide range of symptoms, which differ depending on which nerves are affected.

Examples of symptoms caused by damage to sensory nerves controlling sensitivity are listed below:

• paresthesia, for example, prickling sensations, formication (a sensation of insects crawling on the skin) or the feeling of being pricked by a needle
• itching, numbness
• stabbing or burning pain – occurring spontaneously or due to light touch (e.g. through clothing)
• a feeling of being cramped, unpleasant feelings of pressure or a sensation of walking “on cotton wool”
• decreased sensitivity or lack of sensitivity to temperature changes
• unsteady gait, particularly in the dark
• painless wounds

If motor nerve fibers – the nerves that are important to movement – are affected, the person usually experiences symptoms such as:

• muscle weakness and pain
• muscle twitches and cramps

If nerve damage occurs in the organs, the following symptoms may occur, depending on which organ system is involved:

• heart palpitations when at rest
• feeling dizzy and faint, especially after standing up
• constipation, bloating, diarrhea
• difficulty urinating or bladder weakness (incontinence)
• decreased or increased sweating
• erectile dysfunction in men

The peripheral nerves are sensitive to inflammatory processes in the body, which can be caused, for example, by infections or exposure to toxic substances (cytotoxins) such as alcohol.

This can cause damage to the protective sheath surrounding the nerve fibers (the myelin sheath) or to the nerve fibers themselves.

Hereditary factors or diseases such as diabetes can also cause nerve damage.

Other possible causes are:

• an HIV infection that has been present for some time
• kidney diseases at an advanced stage
• cancer
• autoimmune diseases like Guillain-Barré syndrome
• bacterial infections, such as Lyme disease
• an underactive thyroid
• certain antibiotics and drugs used to treat cancer
• a vitamin B12 deficiency, for example, due to rapid weight loss or surgery to treat obesity
• excessive consumption of alcohol and drugs

In very many people with polyneuropathy – especially those in older age – the exact cause remains unknown.

Around 3% of the population will develop polyneuropathy at some point in their lives.

The most common cause is diabetes – almost half of all people with diabetes will develop nerve damage.

Polyneuropathy is similarly common among people with an alcohol dependency.

How polyneuropathy develops varies considerably between individuals.

Damage to sensory nerves (for example, due to poorly managed blood sugar levels) usually develops slowly. Often, the legs are the first to be affected by impaired sensitivity, followed by the hands.

If polyneuropathy is caused by cytotoxins (toxins that kill cells) such as alcohol, progression of the disease depends on how much of the cytotoxin has entered the body – sensory impairment will increase in tandem with alcohol consumption.

If polyneuropathy is caused by inflammatory or inherited conditions, the nerve damage usually progresses on a continuous basis. Depending on the severity of the condition, episodes of rapid progression may be interspersed with stable phases.

To determine what is causing the polyneuropathy, an in-depth consultation with a doctor is required.

The doctor will ask, for example, about:

• which symptoms the patient is experiencing
• when and where these first occurred
• whether it is only the feet and hands that are affected or other parts of the body also
• whether the symptoms are increasing or changing
• whether the patient has any pre-existing conditions
• which medication the patient is taking
• how much alcohol or drugs they consume
• details of their sexual life and whether they have any sexually transmitted infections

A physical examination may also be necessary. This serves to check:

• the patient’s sensitivity to stimuli
• how well they can walk and stand
• whether any muscles are weakened or paralyzed
• how well the reflexes are working

The following methods are used to determine which nerves are damaged and to what extent:

• Electroneurography (ENoG) is a method doctors use to determine how nerve impulses are transmitted and distributed in the body.
• They use electromyography (EMG) to ascertain how well the muscles respond to nerve impulses.

To obtain more information to help track down the cause, they may also test the patient’s urine, blood or cerebrospinal fluid (liquor), take tissue samples or perform genetic testing and use imaging techniques, such as ultrasound and magnetic resonance imaging (MRI).

If polyneuropathy is caused by other conditions, these must be treated first.

Accompanying pain therapy is also important. This usually consists of treatment with antidepressants or anticonvulsants.

Doctors predominantly use antidepressants to treat depression. They cause the body to increase its production of chemical messengers that block the transmission of pain signals. As a result, the perception of pain is weakened. This can also benefit people with polyneuropathy.

Anticonvulsants are drugs used mainly to treat seizures in epilepsy. These drugs inhibit the sensitivity of nerves, reducing pain as a result.

If these do not adequately relieve the pain of polyneuropathy, opioid painkillers may prove effective. However, these should normally be used for short periods only, as they can be addictive.