Causes of Peripheral Neuropathy
Peripheral neuropathy may be either acquired or inherited. Causes of acquired peripheral neuropathy include:
- physical injury (trauma) to a nerve
- autoimmune responses
- nutritional deficiencies
- vascular and metabolic disorders
Acquired peripheral neuropathies are grouped into three broad categories:
- those caused by systemic disease
- those caused by trauma from external agents
- those caused by infections or autoimmune disorders affecting nerve tissue
One example of an acquired peripheral neuropathy is trigeminal neuralgia (also known as tic douloureux), in which damage to the trigeminal nerve (the large nerve of the head and face) causes episodic attacks of excruciating, lightning-like pain on one side of the face.
In some cases, the cause is an earlier viral infection, pressure on the nerve from a tumor or swollen blood vessel, or, infrequently, multiple sclerosis.
In many cases, however, a specific cause cannot be identified. Doctors usually refer to neuropathies with no known cause as idiopathic neuropathies.
Physical injury (trauma) is the most common cause of injury to a nerve. Injury or sudden trauma, from:
Traumatic injury can cause nerves to be partially or completely severed, crushed, compressed, or stretched, sometimes so forcefully that they are partially or completely detached from the spinal cord. Less dramatic traumas also can cause serious nerve damage. Fractured or dislocated bones can exert damaging pressure on neighboring nerves, and slipped disks between vertebrae can compress nerve fibers where they emerge from the spinal cord.
Systemic diseases, including many disorders that affect the entire body often cause metabolic neuropathies. These disorders may include: Metabolic and endocrine disorders. Nerve tissues are highly vulnerable to damage from diseases that impair the body's ability to transform nutrients into energy, process waste products, or manufacture the substances that make up living tissue.
Diabetes mellitus, characterized by chronically high blood glucose levels, is a leading cause of peripheral neuropathy in the U.S. About 60 percent to 70 percent of people with diabetes have mild to severe forms of nervous system damage.
Kidney and liver disorders
Kidney disorders can lead to abnormally high amounts of toxic substances in the blood that can severely damage nerve tissue. A majority of patients who require dialysis because of kidney failure develop polyneuropathy. Some liver diseases also lead to neuropathies as a result of chemical imbalances.
Hormonal imbalances can disturb normal metabolic processes and cause neuropathies. For example, an underproduction of thyroid hormones slows metabolism, leading to fluid retention and swollen tissues that can exert pressure on peripheral nerves.
Overproduction of growth hormone can lead to acromegaly, a condition characterized by the abnormal enlargement of many parts of the skeleton, including the joints. Nerves running through these affected joints often become entrapped.
Vitamin Deficiencies and Alcoholism
Vitamin deficiencies and alcoholism can cause widespread damage to nerve tissue. Vitamins E, B1, B6, B12, and niacin are essential to healthy nerve function. Thiamine deficiency, in particular, is common among people with alcoholism because they often also have poor dietary habits. Thiamine deficiency can cause a painful neuropathy of the extremities.
Some researchers believe that excessive alcohol consumption may, in itself, contribute directly to nerve damage, a condition referred to as alcoholic neuropathy.
Vascular Damage and Blood Diseases
Vascular damage and blood diseases can decrease oxygen supply to the peripheral nerves and quickly lead to serious damage to or death of nerve tissues, much as a sudden lack of oxygen to the brain can cause a stroke. Diabetes frequently leads to blood vessel constriction.
Various types of vasculitis (blood vessel inflammation) frequently cause vessel walls to harden, thicken, and develop scar tissue, decreasing their diameter and impeding blood flow. This category of nerve damage (called mononeuropathy multiplex or multifocal mononeuropathy) is when isolated nerves in different areas are damaged.
Connective Tissue Disorders and Chronic Inflammation
Connective tissue disorders and chronic inflammation cause direct and indirect nerve damage. When the multiple layers of protective tissue surrounding nerves become inflamed, the inflammation can spread directly into nerve fibers.
Chronic inflammation also leads to the progressive destruction of connective tissue, making nerve fibers more vulnerable to compression injuries and infections. Joints can become inflamed and swollen and entrap nerves, causing pain.