Peripheral nerves are those that enervate skin, muscles, and other body tissues. They include motor, sensory, and autonomic nerves. Most of the time when we talk about peripheral neuropathy, we’re referring to the second type: those nerves that transmit touch, pain, heat, and vibration. These are also the most abundant of the peripheral nerves, as they give our brains information about our external world.
Neuropathy in these sensory nerves can manifest as total numbness, or as tingling or burning pain.
But first let’s talk about how things are supposed to work.
Physiology 101: How Nerves Fire
Electricity of all kinds is mediated by positive and negative charges (which is the whole reason external electrical fields can affect us.)
Your nerve cells look like this (below), and consist of the cell body (the bulbous part at the top), axon (the long tail) and dendrites (the little finger-like projections at the end). The axon is covered with a myelin sheath for insulation, mostly made of fat.
Ions (also known as electrolytes) for the most part can’t permeate the cell membrane without the help of transporters, so that the gradient, or difference in charge from the outside to the inside, can be maintained. The exception to this is potassium: it can pass from outside to in as it pleases. But then sodium has to be pumped out to compensate for it, since both sodium and potassium are both positively charged ions.
At rest, the potential inside is maintained at -70mV, compared to a positive charge outside the cell. When the cell body sends the signal, the sodium channels open and positively charged sodium rushes in to the cell. Once the potential reaches +40mV, an action potential shoots down the axon to the dendrites, where it propagates the signal to the next neuron like a relay race.
What Can Go Wrong
Just like any other part of your body, nerves require blood to nourish them with oxygen. Decreased blood flow can therefore be responsible for neuropathy symptoms. Causes for decreased blood flow or oxygenation might be:
- Diabetes, as chronically high blood sugars can damage the blood vessel lining, leading to plaques and restricted blood flow (particularly in the tiny vessels delivering blood to the nerves)
- Physical restriction, such as in sciatica; if a body compartment is compressed, a herniated disc presses on a nerve, or inflammation is present, decreased blood flow can result.
- Oxidative stress can turn oxygen into free radicals, so that not only does it cause damage, but the oxygen is also not available to the nerves.
- Chronic infections. I often see neuropathy, and bizarre neurological symptoms, associated with Lyme Disease and other tick-borne illnesses. In the cases of these infections, neuropathy is generally migratory. Chronic viral infections have also been known to cause neuropathy, though.
- Hypothyroidism. It’s an unusual symptom, but severe and untreated hypothyroidism leads to swelling and fluid retention, which can restrict blood flow to nerves.
- Autoimmunity. Particularly with various types of vasculitis (inflammation of the blood vessels), blood flow can be restricted, though neuropathy can be a feature of a number of different autoimmune conditions.
- Porphyria. Since this disease (primary or secondary) is characterized by an accumulation of the precursors for heme, the part of the red blood cells that bind oxygen, neuropathy is one of its symptoms.
- Iron deficiency, as it decreases oxygen saturation, can cause neuropathy. (There is also a connection between diabetes and iron deficiency, as well.)
- Copper deficiency can cause anemia, which is probably why it has also been associated with neuropathy.
- Chronic Kidney Disease. This is related to iron deficiency (and perhaps diabetes too): the kidneys produce erythropoietin, which tells the bone marrow to make more red blood cells. Therefore, kidney disease can lead to iron deficiency, which can lead to neuropathy.
Another potential cause of neuropathy is damage to the myelin sheath, resulting in poor insulation and thus, short-circuiting of the signal. This is often due to depletion of the precursor macronutrients (fat, particularly essential fatty acids, phospholipids, and cholesterol) and micronutrients (CoQ10 and B vitamins especially, as well as antioxidants). Causes for such depletion include:
- Statin drugs. These necessarily lower cholesterol (that’s what they’re for), but cholesterol is a necessary component of the myelin sheath. They also deplete everything downstream of cholesterol, including CoQ10.
- Alcoholism. Processing alcohol depletes B vitamins, particularly vitamin B1 (thiamine).
- Quinolone antibiotics. Neuropathy from quinolone toxicity can linger long after the antibiotic treatment is completed.
- Pernicious Anemia. This autoimmune condition results in low levels of vitamin B12.
- Stress. Your adrenal glands produce your stress hormones, and the process involves a high demand for B vitamins. This means chronic stress can deplete your B vitamins, and long-term, this can lead to neuropathy.
- Many other medications have been associated with peripheral neuropathy as well, mostly due to vitamin and mineral depletion. Here is a list.
Various other toxic substances can also result in direct nerve damage. This can occur due to:
- Organophosphates (pesticides). You can avoid these by eating your Dirty Dozen fruits and veggies organic, and washing all your fruits and veggies before eating them. But if you spent a lot of time living near or on a farm, you might need some more aggressive solvent detoxification.
- Chemotherapy or radiation treatment. Both are designed to be toxic to the cancer, but unfortunately, collateral damage can occur.
- Heavy metal toxicity, particularly due to arsenic and thallium.
As with any other chronic symptom, treating peripheral neuropathy effectively requires identifying and removing the obstacle to cure (if it is still present), and giving the building blocks necessary to heal.
In cases where the damage has been done, the focus should be primarily on decreasing any lingering inflammation, combatting any remaining oxidative stress, and providing the building blocks needed for repair.