What causes peripheral neuropathy

Overview

Peripheral neuropathy refers to damage to the nerves outside of the brain and spinal cord (the peripheral nervous system). This damage can cause weakness, numbness and pain, usually in your hands and feet. It can also affect other areas of your body. The peripheral nervous system is a complex network of nerves that transmits information between your central nervous system (brain and spinal cord) and the rest of your body. When these nerves are damaged, they can't send signals properly, leading to a variety of symptoms. The causes of peripheral neuropathy are diverse, ranging from chronic conditions to acute injuries and exposures.

Common Causes of Peripheral Neuropathy

Diabetes Mellitus

Diabetes is by far the most common cause of peripheral neuropathy, often referred to as diabetic neuropathy. High blood sugar levels over many years can damage small blood vessels that supply nerves, as well as the nerves themselves. This nerve damage typically starts in the feet and legs and can progress upwards. Up to 50% of people with diabetes develop some form of neuropathy. The longer a person has diabetes and the less controlled their blood sugar, the higher the risk of developing neuropathy.

Autoimmune Diseases

In autoimmune diseases, the body's immune system mistakenly attacks its own tissues, including the nerves. Conditions like rheumatoid arthritis, lupus, Guillain-Barré syndrome, and Sjögren's syndrome can lead to peripheral neuropathy. In Guillain-Barré syndrome, for instance, the immune system attacks the peripheral nerves, causing rapid onset of weakness and sometimes paralysis.

Infections

Certain infections can directly attack nerve tissue or trigger an immune response that damages nerves. Examples include Lyme disease, shingles (herpes zoster), HIV/AIDS, hepatitis B and C, and leprosy. Shingles, caused by the varicella-zoster virus (the same virus that causes chickenpox), can lead to postherpetic neuralgia, a persistent nerve pain condition.

Vitamin Deficiencies and Imbalances

Nerves require certain vitamins to function properly. Deficiencies in vitamins such as B12, B6, B1, and E can lead to nerve damage. Conversely, excessive intake of vitamin B6 can also be toxic to nerves. Alcoholism is a common reason for nutritional deficiencies, as alcohol can interfere with nutrient absorption and is directly toxic to nerve tissue.

Inherited Neuropathies

Some forms of peripheral neuropathy are genetic and passed down through families. Charcot-Marie-Tooth disease is the most common inherited neurological disorder, affecting the peripheral nerves. It typically causes muscle weakness and sensory loss, usually starting in the feet and legs.

Trauma and Physical Injury

Direct injury to nerves, such as from accidents, falls, or repetitive stress (like carpal tunnel syndrome), can cause peripheral neuropathy. Nerve compression, where a nerve is squeezed or put under pressure, is another common cause. This can happen due to bone spurs, fractures, or even prolonged pressure from positions like sitting or sleeping awkwardly.

Toxins and Medications

Exposure to certain toxins and chemicals can damage peripheral nerves. This includes heavy metals like lead and mercury, as well as industrial solvents. Many medications, particularly those used in chemotherapy (chemotherapy-induced peripheral neuropathy or CIPN), can also cause nerve damage as a side effect. Other drugs, including certain antibiotics, antivirals, and heart medications, have also been linked to neuropathy.

Other Causes

Less common causes include kidney disease, liver disease, thyroid disorders (hypothyroidism), tumors pressing on nerves, and certain types of cancer. In a significant number of cases (around 30%), the exact cause of peripheral neuropathy cannot be identified, and it is then termed idiopathic neuropathy.

Understanding Nerve Damage

The peripheral nervous system consists of sensory nerves (carrying sensations like touch, pain, temperature), motor nerves (controlling muscle movement), and autonomic nerves (regulating involuntary functions like heart rate, digestion, and blood pressure). Damage to these different types of nerves can result in a wide array of symptoms:

• Sensory nerve damage: Tingling, numbness, burning sensations, sharp pains, increased sensitivity to touch, loss of balance.
• Motor nerve damage: Muscle weakness, cramps, twitching, loss of muscle control, difficulty with fine motor skills, foot drop.
• Autonomic nerve damage: Problems with digestion (nausea, vomiting, diarrhea, constipation), abnormal sweating, bladder control issues, dizziness upon standing (orthostatic hypotension), erectile dysfunction.

The specific symptoms and their severity depend on which nerves are affected and the extent of the damage. Early diagnosis and management of the underlying cause are crucial for preventing further nerve damage and managing symptoms effectively.