Nerve damage, also known as neuropathy, refers to injury or dysfunction of one or more nerves. This can result in numbness, tingling, pain, muscle weakness, and other symptoms. Nerve damage can be caused by a wide range of underlying conditions and diseases. Some common causes include diabetes, autoimmune disorders, infections, trauma, toxins, tumors, and nutritional deficiencies. Determining the underlying cause is important for proper treatment and management of the nerve damage. In this article, we will discuss some of the most common medical conditions associated with nerve damage and the mechanisms by which they damage nerves.
Diabetes
Diabetes is one of the most common causes of nerve damage. Approximately 50% of diabetics develop some type of neuropathy. High blood glucose levels associated with diabetes can damage nerves in several ways:
– Increased sorbitol production inside nerve cells leads to osmotic stress and cell damage
– Glycation of proteins and lipids leads to dysfunction of cellular proteins and structures
– Ischemia from microvascular disease decreases blood supply to nerves
– Oxidative stress from reactive oxygen species damages neurons
– Mitochondrial dysfunction and altered gene expression contribute to neuronal injury
The most common forms of diabetic neuropathy include peripheral neuropathy, autonomic neuropathy, and focal neuropathy. Peripheral neuropathy typically causes numbness, tingling, and pain in the feet, legs, hands, and arms. Autonomic neuropathy affects automatic functions like heart rate, digestion, and bladder control. Focal neuropathy affects specific nerves, often causing sudden weakness of facial muscles or foot drop.
Controlling blood glucose levels through diet, exercise, medication, and insulin helps prevent and manage diabetic nerve damage.
| Type | Description | Symptoms |
|---|---|---|
| Peripheral Neuropathy | Damage to peripheral nerves in the feet, legs, hands, and arms | Numbness, tingling, burning pain, hypersensitivity, muscle weakness |
| Autonomic Neuropathy | Damage to nerves controlling automatic functions | Orthostatic hypotension, gastrointestinal issues, bladder dysfunction, sexual dysfunction |
| Focal Neuropathy | Damage to specific nerves | Weakness or paralysis of facial muscles, foot drop, pain |
Autoimmune Diseases
Autoimmune diseases like rheumatoid arthritis, lupus, and Sjogren’s syndrome are associated with several types of neuropathy. In these conditions, the immune system mistakenly attacks the body’s own tissues, including nerves. Some mechanisms include:
– Inflammation damages the blood vessels supplying nerves
– Antibodies directly target and damage nerve cells or myelin sheath
– Immune complexes deposit in nerves and cause local inflammation
– Cytotoxic T cells directly kill nerve cells
The most common neuropathies associated with autoimmune disease are sensory predominant with numbness and paresthesias. Autonomic neuropathy can also occur. Immunosuppressant medications like corticosteroids and disease-modifying anti-rheumatic drugs can help treat the neuropathy by suppressing the overactive immune system.
Infections
Infections can also lead to nerve damage, either directly through the neurotoxic effects of the pathogens or indirectly through inflammation. Common infections associated with neuropathy include:
HIV/AIDS
– Direct injury to nerve cells by the HIV virus
– Opportunistic infections
– Nutritional deficiencies
– Side effects of medications
Sensory neuropathy with pain and paresthesias in the feet is most common. Autonomic neuropathy also frequently occurs. Anti-retroviral medications, treatment of opportunistic infections, and managing nutrition can help prevent and treat HIV neuropathy.
Herpes Viruses
– Viruses like herpes simplex, varicella zoster, Epstein-Barr, and cytomegalovirus can directly infect nerve cells
– Acute viral infection causes inflammation and damage to nerve fibers
– Post-herpetic neuralgia is a common complication following shingles
Antiviral medications can treat active viral infections. Tricyclic antidepressants, anticonvulsants, opioids, and topical medications help manage post-herpetic neuralgia.
Leprosy
– Mycobacterium leprae infects Schwann cells in peripheral nerves
– Inflammatory damage to myelin sheath and axons
Antibiotics like dapsone and rifampin treat leprosy. Corticosteroids and immunosuppressants can help manage nerve inflammation.
Toxic Neuropathies
Exposure to certain toxins and drugs can be associated with nerve damage. These include:
Chemotherapy
– Platinum agents like cisplatin, taxanes, vinca alkaloids, and thalidomide used to treat cancer are neurotoxic.
– Cause sensory neuropathy with numbness and paresthesias
Dose reduction, treatment delays, or change to less toxic drugs can help prevent permanent neuropathy. Symptomatic treatment helps manage discomfort.
Heavy Metals
– Lead, mercury, arsenic, and thallium can damage nerves
– Industrial exposures more common in the past before workplace regulations
– Paresthesias, muscle weakness, sensory changes
Avoiding further exposure and chelation therapy can remove heavy metals from the body and limit neuropathy.
Organophosphates
– Pesticides and nerve agents chemically inhibit acetylcholinesterase enzyme
– Causes autonomic dysfunction, muscle weakness, seizures
– Atropine can reverse symptoms in acute poisonings
Alcohol
– Chronic heavy alcohol use is associated with peripheral neuropathy
– Exact mechanism uncertain but likely involves nutritional deficiencies like vitamin B12
– Abstinence from alcohol and nutritional supplementation can help improve neuropathy
Physical Trauma
Physical injuries that sever or compress nerves can obviously cause neuropathy through mechanical damage. This includes injuries from accidents, surgery, fractures or dislocations, lacerations, projectile wounds, and more. Prompt surgical repair is important for nerve regeneration. Physical therapy helps prevent atrophy and maintain function during recovery.
Tumors
Cancers like lymphoma, leukemia, and multiple myeloma can infiltrate or apply pressure to peripheral nerves. Tumors in the brain and skull can compress cranial nerves. Signs of cranial nerve impingement include facial weakness or numbness, vision changes, hearing changes, vertigo, swallowing difficulties, and more depending on the nerve affected. Treating the underlying tumor with radiation, chemotherapy, or surgery can help relieve nerve compression.
Nutritional Deficiencies
Deficiencies in certain vitamins, minerals, and nutrients can predispose to neuropathy or make existing neuropathy worse:
Vitamin B12
– Important for myelin production and neuronal function
– Pernicious anemia, celiac disease, gastric bypass surgery increase risk of deficiency
– Causes subacute combined degeneration with gait problems, vibration sense loss
Vitamin B1 (Thiamine)
– Essential for nerve conduction
– Deficiency associated with alcoholism, malnutrition
– Causes dry beriberi neuropathy
Vitamin B6 (Pyridoxine)
– Role in neurotransmitter synthesis
– Isoniazid medication can deplete B6
– Sensory neuropathy in feet and hands
Vitamin E
– Fat soluble vitamin with antioxidant properties
– Gastrointestinal disorders can impair absorption
– Ataxia, proprioceptive deficits in legs
Copper
– Required for iron absorption and neurological enzymes
– Gastrointestinal surgery increases risk of deficiency
– Sensory ataxia and spastic gait abnormalities
Screening for nutritional deficiencies in at risk patients can identify treatable causes of neuropathy. Vitamin supplementation or dietary changes can resolve neuropathy in some cases.
Genetic Neuropathies
There are over 100 genetic mutations associated with inherited neuropathies. These conditions directly impair neuronal function through problems with protein production, mitochondrial function, myelin structure, axonal transport, and other cellular processes. Genetic testing can identify the specific mutation to help guide treatment and prognosis. Examples include:
– Charcot Marie Tooth – mutated genes affect myelin production
– Friedreich’s ataxia – repeat expansion causes mitochondrial protein deficiency
– Small fiber neuropathies – sodium channel mutations enhance pain signaling
– Fabry disease – enzyme deficiency leads to nerve fiber lipid deposits
Treatment focuses on symptom management. Physical therapy maintains mobility and function. Genetic counseling provides information on inheritance patterns and reproductive options. Enzyme replacement or gene therapy offer hope for treating certain genetic neuropathies in the future.
Idiopathic Neuropathy
In up to a third of neuropathies, no definite cause can be identified. This is termed idiopathic neuropathy. Suspected mechanisms include microvascular damage from diabetes or hypertension and autoimmune-mediated nerve damage in patients who test negative for autoantibodies. Managing symptoms, lifestyle modifications, and treating coexisting medical conditions are the main approaches for idiopathic neuropathies.
Conclusion
In summary, diverse medical diseases, toxins, trauma, genetics, and nutritional deficiencies can contribute to neuropathy. Identifying and addressing the root cause is key for neuropathy treatment and prevention. Controlling associated diseases like diabetes, managing deficiencies with diet and supplements, eliminating neurotoxic exposures, and prompt surgical repair of damaged nerves can all protect nerve health and minimize permanent deficits. Research continues to uncover new causes, treatments, and neuroprotective strategies to improve outcomes in various neuropathies. An interdisciplinary approach with good communication between specialties ensures optimal care for neuropathy patients.