Peripheral Neuropathy

Peripheral neuropathy is a medical condition in which the nerves outside of your brain and spinal cord—called peripheral nerves—are damaged. This can cause mild to severe pain, numbness, muscle twitching, and other symptoms in the hands, feet, and other parts of the body.

The peripheral nervous system is one of two parts of the nervous system. It is made up of nerves that relay messages back and forth to the central nervous system (comprised of the brain and spinal cord). Peripheral nerves not only control muscle movements but a regulate involuntary functions like digestive and heart rate, and provide sensations such as itching, warmth, or pain.

Alcohol abuse, autoimmune diseases, toxins, medications, and diseases like shingles and diabetes are among the many conditions that can cause peripheral neuropathy. Peripheral neuropathy can't always be cured, but it can be managed.

This article explains types of peripheral neuropathy, how it affects your body, and ways to manage the condition.

Types of Peripheral Neuropathy

There are many causes of peripheral neuropathy, each of which has different symptoms and affects different parts of the body. The approach to treatment can also vary.

Peripheripheral neuropathy can be broadly categorized by the number of nerves affected and subcategorized by the underlying cause of the nerve damage and the type of nerves affected.

Mononeuropathy

Mononeuropathy is a type of neuropathy involving only one nerve. It can result from direct nerve injury, nerve compression, or reduced blood flow (ischemia) to a nerve.

Mononeuropathy is localized (limited to a part of the body) and may worsen with certain movements or activities.

Common causes of mononeuropathy include:

• Carpal tunnel syndrome
• Axillary nerve palsy (nerve compression caused by shoulder dislocation)
• Brachial plexus compressive (nerve compression associated with using crutches)
• Radiation-induced nerve injury

Polyneuropathy

Polyneuropathy is when many nerves in various body parts are affected. It is a more complicated condition that usually arises from a systemic (whole-body) disease. Symptoms tend to develop gradually rather than abruptly.

Polyneuropathy is strongly associated with a process called demyelination in which the insulating coating of nerve cells, called myelin, is either damaged or stripped away. When this happens, peripheral nerve cells can "misfire" and trigger nerve pain and other neuropathy symptoms.

Polyneuropathies are usually bilateral (affecting both sides of the body) and symmetrical (affecting both sides of the body equally). The hands and feet are most commonly involved.

Common causes of polyneuropathy include:

• Diabetic neuropathy (caused when high blood sugar damages peripheral nerves)
• Alcoholic neuropathy (caused by the demyelinating effect of alcohol)
• Certain infections (including Lyme disease, hepatitis C, and HIV)
• Vitamin B12 deficiency (which slows production of myelin)
• Kidney failure (which causes the accumulation of toxins that damage peripheral nerves)
• Autoimmune conditions (like lupus, celiac disease, vasculitis, and Guillain-Barré syndrome that directly attack peripheral nerves)
• Postherpetic neuralgia (long-lasting nerve damage caused by shingles)
• Paraneoplastic syndrome (caused when cancers like lung cancer, multiple myeloma, or lymphoma produce chemicals that damage peripheral nerves)
• Charcot-Marie-Tooth disease (a rare inherited nerve disorder)
• Heavy metal poisoning (including lead and mercury)
• Certain medications (like chemotherapy, certain HIV drugs, and antibiotics like dapsone)

Mononeuritis Multiplex

Mononeuritis multiplex falls somewhere between mononeuropathy and polyneuropathy. It is caused when two or more separate nerve bundles are simultaneously affected.

It is differentiated from polyneuropathy in that it tends to be unilateral (one-sided). With that said, the condition can sometimes progress and affect both sides of the body asymmetrically.

Mononeuritis multiplex is also associated more with the loss of sensory or motor function of individual nerves. Oftentimes, the pain, if any, may be deep and aching rather than sharp and severe.

Causes of mononeuritis multiplex can overlap with those of polyneuropathy, including:

• Diabetes
• Autoimmune diseases (like lupus and rheumatoid arthritis)
• Vasculitic neuropathy (caused by blood vessel diseases like granulomatosis with polyangiitis)
• Certain infections (like Lyme disease, HIV, and leprosy)
• Sarcoidosis (an inflammatory disease that causes granular lumps throughout the body)
• Cryoglobulinemia (a condition in which cold temperatures cause proteins in blood vessels to clump and block off circulation)

Peripheral Neuropathy Symptoms

Peripheral neuropathy affects peripheral nerves. These include sensory nerves that provide sensations, motor nerves that regulate voluntary muscle movements, and autonomic nerves that regulate involuntary muscle movements.

Damage to these nerves can cause "negative" symptoms (meaning the loss of normal function) or "positive" symptoms (meaning new problems that arise because of nerve damage).

Sensory Symptoms

Abnormal sensations are the main body of symptoms most people associate with peripheral neuropathy. Many of these sensations are caused by damage to sensory nerves called nociceptors that process pain signals and proprioceptors that help us maintain our body position in space.

Damage to this body of nerves can cause:

• Nerve pain (neuralgia)
  
• Numbness, tingling, burning, prickly, skin-crawling, itching, “pins-and-needles” sensations (paresthesias)
• Oversensitivity to things that usually don't cause pain (hyperalgesia)
• Difficulty balancing and coordinating movements, like walking, due to the lack of awareness of where your feet or body parts are (loss of proprioception)

Motor Symptoms

Motor nerves regulate the musculoskeletal system which enables locomotion (movement) and the articulation of joints. This differs from proprioception in that it involves the loss of motor function rather than sensory function.

Motor symptoms of peripheral neuropathy include:

• Muscle twitching or cramps
• Muscle weakness or paralysis affecting one or more muscles
• Muscle wasting (atrophy)
• Difficulty lining up your feet or lifting your foot and toes ("foot drop")

Autonomic Symptoms

Autonomic neuropathy is caused by damage to autonomic nerves that regulate heart, digestive, urinary, and other involuntary bodily functions.

Disruption of these systems can lead to:

• Loss of bladder control (urinary incontinence)
• Loss of bowel control (fecal incontinence)
• Difficulty swallowing (dysphagia)
• Changes in bowel movements (intestinal dysmotility), causing diarrhea or constipation
• Rapid heartbeats (tachycardia) or slower heartbeats (bradycardia)
• Abnormally slowed breathing (bradypnea) or shallow breathing (hypopnea)
• Central sleep apnea (gaps in breathing during sleep caused by nervous system dysfunction)
• Inability to regulate body temperature
• Feeling faint or dizzy when sitting or standing (orthostatic hypotension)
• Sexual dysfunction (including erectile dysfunction and orgasm/arousal problems)
  

Diagnosing Peripheral Neuropathy

The diagnosis of peripheral neuropathy starts with a review of your medical history, a physical exam, and a neurological examination (to determine the extent of your negative and positive symptoms). Additional tests and procedures may be ordered to narrow the possible causes.

Neurological Exam

During a neurological exam, your healthcare provider will check your reflexes and evaluate for sensory dysfunction—especially on your feet and hands—using vibration, temperature, and pinprick. Your muscle strength and gait will also be evaluated.

Blood Tests

In addition to the neurological exam, your healthcare provider will order a series of blood tests to narrow the possible causes of your peripheral neuropathy.

Some of the more common include:

• Complete blood count (CBC)
• Comprehensive metabolic panel (CMP)
• Erythrocyte sedimentation rate (ESR)
• Fasting blood glucose
• Vitamin B12 level
• Thyroid-stimulating hormone

Autoantibody testing may be ordered if an autoimmune disease is suspected, while disease-specific tests for HIV, Lyme disease, and hepatitis C can diagnose these diseases with a simple blood test. Genetic testing can help detect diseases like Charcot-Marie-Tooth disease.

Nerve Tests

Certain nerve tests can help confirm the diagnosis and characterize the extent of your peripheral neuropathy. They can also help exclude certain causes, like nerve compression, to support the diagnosis.

These may include:

• Nerve conduction velocity study (NCV)
• Electromyography (EMG)
• Nerve biopsy or neurodiagnostic skin biopsy

Autonomic Tests

For people with autonomic symptoms, various tests can aid in the diagnosis. Examples include measuring your blood pressure on a tilt table (used to check for orthostatic hypotension) or conducting a thermoregulatory sweat test to see if your body regulates temperature normally.

Other Tests

Because the causes of peripheral neuropathy are many, other tests may be needed to diagnose and confirm the underlying condition. Examples include a lumbar puncture (spinal tap) to confirm a diagnosis of Guillain-Barré syndrome, or a 24-hour urine collection to check for possible heavy metal exposure.

Treating Peripheral Neuropathy

The treatment of peripheral neuropathy differs based on the underlying cause. In some cases, the resolution of an infection or the discontinuation of a drug is all that is needed to clear the symptoms.

At other times, ongoing management of the underlying cause (like diabetes, kidney disease, or lupus) may be needed to keep your symptoms under control.

Easing Symptoms

In severe or chronic (persistent) cases, medications may be prescribed. This can be challenging because some work better for some people than others and none have been consistently effective across different diseases.

Some of the most common drugs used for peripheral neuropathy include:

• Transdermal pain patches, including over-the-counter products like Lidoderm (lidocaine 5% patch) or prescription products like Qutenza (capsaicin 8% patch)
• Tricyclic antidepressants, such as nortriptyline, amitriptyline, imipramine, and desipramine
• Serotonin-norepinephrine reuptake inhibitors (SNRIs), such as duloxetine, venlafaxine, and milnacipran
• Anticonvulsant drugs, like gabapentin, pregabalin, oxcarbazepine, lamotrigine, topiramate, clonazepam, and phenytoin, sodium valproate, and carbamazepine
• Opioid painkillers, like buprenorphine, fentanyl, tramadol, and oxycodone

In addition to medications, physical therapy or assistive walking devices can help people with neuropathy-related weakness and balance problems.

Summary

Peripheral neuropathy is a condition caused by damage to the peripheral nerves. The damage can cause pain, abnormal sensations, movement problems, and organ dysfunction based on which peripheral nerves are affected (including motor, sensory, or autonomic nerves).

There are many causes of peripheral neuropathy, including nerve compression, diabetes, autoimmune disorders, infections, toxins, medications, and nutritional deficiencies. The treatment of peripheral neuropathy varies by the cause but may involve prescription antidepressants, anticonvulsants, and opioid painkilers to help alleviate symptoms.