The nervous system forms a very intricate communication network between the parts of our body and the brain. Neuropathy is a condition where the nerve is damaged or diseased.
Nerve damage interrupts the line of communication, and this disturbance leads to reduced or lack of function of the body part connected to the damaged nerve.
Neuropathies can be acute or chronic. The symptoms may arise suddenly, worsen and then resolve slowly as the nerves heal.
However, in chronic conditions, the symptoms may take awhile to develop and manifest and progress slowly. Some individuals experience relief for awhile after which the symptoms return.
How common is neuropathy?
Around 20 million individuals in US alone experience some types of peripheral neuropathies.
A recent study published in Nature Reviews Disease Primers, 2017 states that around 7-10% of the general population experiences neuropathic pain. Scientific evidence has linked neuropathic pain with increased drug prescriptions and visits to the doctor.
Chronic neuropathic pain is more frequent in women than men. Most patients with neuropathic pain are below the age of 50 years.
Diabetic neuropathy is the most common form of peripheral neuropathies. Neuropathic pain commonly affects the neck, upper limbs, lower back and lower limbs.
What are the types of neuropathy?
According to NIH, they are 100 types of peripheral neuropathy, and each has different symptoms. The most basic classification of neuropathy is:
• Mononeuropathies: Only one nerve is damaged
• Polyneuropathy: Multiple nerves damaged
They can be classified based on the damage that has occurred:
• Damage to the axon on threadlike structure of the nerve cell
• Damage to the myelin sheath or the coat that covers a nerve cell
• Combination of the above two types of damage
Based on causative factors they can be briefly classified as :
• Idiopathic: No known cause
• Diabetic: A result of diabetes complications
• Hereditary: Due to genetic lineage or sudden genetic defects
• Toxins or due to medications: A result of exposure to certain toxins, or intake of certain drugs, alcohol
• Inflammatory: This could be due to infections (HIV, Lyme) or Autoimmune conditions (Lupus)
• Systemic/Metabolic: Due to pre-diabetes, alcohol, nutritional deficiencies, etc.
• Compression: Such as carpal tunnel syndrome or amyloidosis
What are the symptoms of neuropathy?
Neuropathy symptoms are mainly listed as tingling or prickling sensations. However, symptoms depend on the type of the nerves damaged.
The most common symptom reported by patients is numbness. The feeling of numbness widens to abnormal sensations, pins, and needles, tingling, electric shock-like sensations, feeling of heaviness, etc. Clinically these symptoms are known as paresthesia.
Neuropathic pain is reported by at least 60% of the patients with chronic neuropathies. This pain stems from damage or lesions to the nerve.
Damage to the sensory nerve fibers leads to increased sensitivity in the affected area and disturbs the pain signals. This could involve allodynia which is a pain in response to a stimulus that would not cause pain such as pain in response to wrapping a blanket gently on your body.
Also, there may be heightened pain response in the presence of a stimulus that causes slight pain (hyperalgesia).
Neuropathic pain can cause sleep disturbances and contribute to anxiety and depression.
Based on the type of nerves affected, following symptoms could occur :
Symptoms of Motor nerve damage
Motor nerves are involved with our movement, limb reflexes, and coordination. Damage to these nerves can lead to muscle weakness, reduced muscle function and reflexes, twitching, loss of muscle mass, cramps, etc.
Symptoms of Sensory nerve damage
Sensory nerves are linked with our ability to feel such as pain, touch, temperature, etc. Damage to these nerves can cause decreased sensations. Patients may get a feeling as though they are wearing gloves or stockings.
It can lead to loss of coordination, reduced sensation of pains or wounds, inability to balance when eyes are shut. Diabetic neuropathy commonly involves sensory nerve damage.
Symptoms of Autonomic nerve damage
The autonomic nervous system controls our involuntary functions such as breathing, blood circulation, sweating, etc.
Damage to these nerves can cause serious symptoms such as loss of bladder control, gastric symptoms due to damage to associated nerves, heat intolerance, inability to sweat normally.
It may even affect blood pressure control leading to dizziness or fainting. Some individuals may experience difficulty in swallowing or even breathing.
What are the causes of neuropathy?
Idiopathic neuropathies have no known causes. Acquired neuropathies may have some causative factors which have been listed below :
• Injuries: Accidents, sports injuries or surgical procedures may cause serious direct or indirect damage to the nerves.
• Repetitive stress: Unhealthy and repetitive movement of joints for long periods can compress and damage nerves near the joint.
• Toxins: Exposure to environmental toxins (heavy metals), side effects of medications (chemotherapeutic agents) or excessive intake of alcohol could cause neuropathy.
• Metabolic and hormonal disorders: Disturbance in hormonal levels can contribute to neuropathies.
• Vascular diseases: Vasculitis or inflammation of blood vessels can interrupt blood flow and lead to nerve damage.
• Infections: Viruses such as those involved in HIV and shingles can attack and damage nerves.
• Autoimmune conditions: Chronic autoimmune disorders such as Sjogren’s syndrome and Rheumatoid arthritis can create a state of inflammation which damages nerves.
• Kidney disorders: Decrease in kidney function to eliminate toxins can, in turn, affect nerve health.
• Cancer and tumors: Cancers can invade nerve tissue and compress the nerves. Benign tumors such as neuromas can lead to increased growth of nerve tissue and cause nerve compression. Toxicity of chemotherapeutic agents may also cause neuropathy.
Pathophysiology of Various Neuropathy Types: What Happens in Your Body In Neuropathy?
In diabetes, glucose metabolism is hampered, and this creates a state of increased blood sugar levels. This state is not conducive to the survival of nerves. Also, it creates an imbalance of prooxidant and antioxidant agents, and this leads to oxidative damage.
Oxidative damage produces toxic end products that damage nerves. Repair mechanism is impaired in diabetes. A reduction in neurotrophic agents (proteins that support healthy nerve growth) is observed in diabetes.
Neuropathy in cancer can occur due to the toxic action of cancerous cells or due to an autoimmune response of the body. Even chemotherapy can cause neuropathy in multiple nerves.
Paclitaxel, vincristine, and cisplatin are few chemotherapeutic agents that cause neuropathies. Radiotherapy and surgery may contribute to painful peripheral neuropathy in cancer.
Autoimmune disease-associated neuropathies
Autoimmune diseases like Sjogren’s syndrome, rheumatoid arthritis, lupus create a chronic state of inflammation which is unfavorable for nerve health. 33% of the patients with these autoimmune conditions develop carpal tunnel syndrome and tenosynovitis.
Further, if the inflammation spreads to blood vessels (vasculitis), it hardens the walls of blood vessels and impairs blood flow which is vital for the survival of nerves.
Infectious conditions associated neuropathies
Viruses like Epstein Barr virus, Herpes Simplex virus, Varicella-Zoster virus attack nerve tissue and cause intense neuropathic pain. Tick-borne infections and Lyme disease can cause painful polyneuropathy within a few weeks of infection.
1/3 of the individuals with AIDS experience peripheral neuropathy. Various factors are responsible for this such as a decrease in immunity, malnutrition, vitamin B12 deficiency, inflammation, increased oxidative stress, etc.
Drug-induced neuropathy is said to be a result of disruption of the nerve-blood barrier which is comparable to the blood-brain barrier.
Anti-retroviral drugs used in HIV can impair cellular respiration and cause nerve damage. Chemotherapeutic agents at high doses cause neuropathies and may even serve as neurotoxic agents.
Lipid-lowering drugs or statins interfere with cholesterol synthesis, affect antioxidant defenses and impair respiratory units of nerve cells, thus leading to nerve damage.
Excessive alcohol intake can cause nutritional deficiencies such as vitamin B deficiencies which affect nerve health.
Toxic effects of alcohol consumption, poor liver health, malnutrition, genetics are certain factors that contribute to alcohol-induced neuropathy.
80% of the individuals with advanced kidney failure experience painful polyneuropathy.
Reduced elimination of toxins, electrolyte imbalance, and an increase in the level of neurotoxins in the body are a few factors that decrease energy production which is necessary for the survival of nerve cells.
What is the treatment available for neuropathy?
Treating underlying conditions
This could involve treatment of infections, reduction of toxin exposure, managing autoimmune conditions and resolving nutritional deficiencies.
Changing lifestyle habits, eating a balanced diet, rectifying nutritional deficiencies, reducing toxin exposure, limiting alcohol intake are few of the measures. Exercise can help reduce cramps and loss of muscle mass.
Self-care and proper wound treatment can benefit in diabetic neuropathy. Treating diabetes or other autoimmune conditions can help mitigate certain neuropathic symptoms.
Slight incidences of pain can be resolved with over the counter medications. Chronic pain may require treatment with other medications such as antidepressants and anticonvulsants.
Antiepileptics like pregabalin and gabapentin are commonly prescribed to treat neuropathic pain. These can be combined with antidepressants such as amitriptyline or duloxetine or even opioids for a significant therapeutic effect.
Topical agents such as lidocaine (anesthetic) or capsaicin gel can be prescribed for localized pain.
Nerve and Brain Stimulation
This could involve stimulation of the spinal cord or certain nerve fields with low-intensity electric signals.
Stimulation of the brain by treatments such as Epidural motor cortex stimulation (ECMS), repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) is found to be beneficial.
Chronic pain can affect the quality of life and contribute to anxiety and depression. Individuals do try to adapt to the pain they face, but some may require therapeutic guidance.
Cognitive Behavioural Therapy aims to help mitigate psychological symptoms, functional symptoms and improve social engagement in neuropathy.
Though neuropathies are rarely fatal, they can be potentially debilitating. Neuropathic pain that arises from nerve damage is extremely painful with a burning sensation, and this can last for very long periods. This disturbs the patient’s quality of life.
Neuropathies affecting autonomic nervous systems can have serious symptoms such as difficulty in swallowing or breathing. Treatment for neuropathies requires successful diagnosis.
Patients who are at increased risk of developing neuropathy should be educated about the condition and possible preventive measures.
Apart from symptomatic treatment, research should focus on identifying potential neuroprotective agents that can help repair damaged nerves.