Peripheral Neuropathy
Peripheral Neuropathy is a condition that affects about 1% of the population world wide and about 8% of people older than 65 years. You may have heard of the terms polyneuropathy, mononeuropathy, multifocal neuropathy or just neuropathy that are often used synonymously for peripheral neuropathy. But do they really all mean the same thing? In my research for this video I found that the terminology around peripheral neuropathy is quite confusing.
Before we shed some light on what all these different terms mean, let’s take a look at our nervous system as this will help us understand the differences.
The nervous system is a highly complex system that transmits signals between body parts. It consists of the central nervous system, short CNS, and the peripheral nervous system, short PNS. The CNS is made up of the brain and the spinal cord and the PNS is made up of nerves outside of the CNS. Central Nervous System and Peripheral Nervous System work closely together to allow super fast transmission of signals from the brain to the rest of the body and the other way around. The cells through which those signals are transmitted are called neurons and signal transmission occurs chemically as well as electronically.
Going back to our confusing terminology. Neuropathy is a very broad term describing any kind of nerve damage. Peripheral Neuropathy specifies that we’re talking about nerve damage of the peripheral nervous system as opposed to nerve damage of the central nervous system. Mononeuropathy, polyneuropathy and multifocal neuropathy are all subtypes of peripheral neuropathy. Mononeuropathy means that only one nerve is affected whereas polyneuropathy means that multiple nerves are affected. In multifocal neuropathy we’re dealing with a combination of affected nerves all located in the same area.
There are many different causes of peripheral neuropathy and symptoms vary widely. We’ll go into more details about that in a minute but first let’s talk about what different kinds of nerves exist because that information will help us understand the variety of symptoms.
Sensory nerves. Sensory nerves transmit signals from your sensory organs to your brain where they get processed. For example, if your house is on fire, your nose will smell the smoke and sensory nerves will transmit that information to your brain which will translate the signal and activate your motor nerves to get to safety. Other senses are sight, hearing, taste and touch.
Motor nerves. Motor nerves transmit signals in the opposite direction compared to sensory nerves. As in the example I just mentioned, the brain initiates the signal that there is danger which travels through your motor nerves to your legs. You will then get up and leave the burning house.
The third type of nerves are autonomic nerves. Those nerves are outside of our direct control and regulate bodily functions such as breathing, digestion, sweating, heart rate, blood pressure, and bladder control.
So, what are the symptoms we see in patients with peripheral neuropathy?
Symptoms vary widely and depend on the kind of nerve that is affected. There is also a difference between so-called negative symptoms and positive symptoms. A negative symptom basically describes the loss of something. For example paresis, which is the weakening of muscles or you could say the loss of muscle strength. Another example is sensory impairment, in which patients lose their sensitivity to certain sensory signals.
Positive symptoms describe the gain of something. For example muscle cramps, muscle twitches, or pain.
Here are some common symptoms for the three different types of nerves I just described:
Sensory Nerves: Symptoms include: sensation of furriness and numbness; paresthesia, which describes a tingling, burning or cold sensation of the skin. Maybe you’ve heard of the term pins and needles. Then there is electric shock-like pain, gait instability and falls.
Motor Nerves: Symptoms include: weakness and muscle loss, muscle cramps and twitches.
Autonomic Nerves: Symptoms include: dry skin, bladder dysfunction, diarrhea, rapid heartbeat, and body hair loss.
This sounds all pretty awful! What causes peripheral neuropathy?
There are different causes of peripheral neuropathy and they affect different nerves or even different parts of the nerve cells, too. Let’s take a quick look at what a nerve cell, called a neuron looks like.
A neuron has a cell body that contains the nucleus, dendrites, which receive signals from other cells, a long axon, which transmits signals to the axon terminal where we can find the synapses. Synapses transmit electrical and chemical signals to other cells. Some neurons also have a protective layer around the axon, which is called myelin sheath. You can compare the myelin sheath to insulation around an electrical cord. The insulation allows faster transmission of the signal while ensuring that the signal doesn’t get lost.
Peripheral neuropathy can occur when either the axon or the myelin sheath is damaged. Here are the different causes of peripheral neuropathy:
Metabolic causes: The most common metabolic cause of peripheral neuropathy is diabetes. With rising diabetes rates in the western world, we also see a sharp increase in peripheral neuropathy cases. Up to 54% of type 1 diabetes patients develop peripheral neuropathy and for type 2 diabetics the number is up to 46%. Blood sugar control and lifestyle changes can reduce symptoms. Other metabolic causes of peripheral neuropathy are vitamin deficiencies, such as B12 and B6 deficiency. Supplementation of those vitamins reduces symptoms and may even stop them altogether. Caution is warranted with B6 deficiency, as too much vitamin B6 can also cause peripheral neuropathy.
Toxic causes: The most common cause of peripheral neuropathy induced by a toxin is chemotherapy-induced peripheral neuropathy. With better understanding of cancer and the development of more chemotherapy for treatment, there is also an increase in chemotherapy-induced peripheral neuropathy. This is often a long-term side effect of chemotherapy treatment that patients may suffer from for years or even the rest of their lives. Treatment for this is mainly aimed at managing the symptoms. Other toxins that can induce peripheral neuropathy include chloroquine, which is an example of anti-infective agents, and environmental toxins such as arsenic, lead, mercury, acrylamide, carbon disulfide and others. There are multiple drugs for other conditions that have also been associated with the development of peripheral neuropathy. In the case of toxin-induced peripheral neuropathy, avoiding exposure to the toxin often reduces or removes symptoms. It is important to identify the cause of peripheral neuropathy as early as possible if caused by a toxin to prevent major nerve damage.
An overlap of metabolic and toxic causes is alcohol-induced peripheral neuropathy. Consumption of alcohol negatively impacts the absorption of nutrients which can lead to deficiencies such as thiamine, folate, niacin, or vitamins E, B6 and B12 deficiencies. This does not happen due to your occasional glass of wine that you enjoy with dinner. But it is found in about 66% of alcoholics.
Immune-mediated peripheral neuropathy: In this case, an auto-immune reaction attacks the neurons and causes damage. The most common example for this is the Guillain-Barre Syndrome which often occurs as a result of an infection. Here we’re dealing with a very acute situation that needs immediate diagnosis and treatment. Another example of immune-mediated peripheral neuropathy is CIDP, which stands for chronic inflammatory demyelinating polyradiculoneuropathy. As the name says, this is a chronic condition and it specifically attacks the myelin sheath.
Accidents and repetitive motions: Peripheral Neuropathy, or in this case often multifocal neuropathy, may also be caused by accidents or repetitive motions that lead to a wear and tear of nerves. One well known example for this is carpal tunnel syndrome. In such cases, physiotherapy or potentially surgery can help with symptoms.
Last but not least, peripheral neuropathy can also be caused by hereditary diseases. The most common example for that is Charcot-Marie-Tooth disease (CMT) which has a prevalence of about 40-80 in 100,000 people. Here, patients carry mutations in structural proteins of the myelin sheath or proteins involved in axonal transport and mitochondrial metabolism.
A diagnosis of the underlying cause of peripheral neuropathy is crucial as treatment options vary widely. Different methods to diagnose peripheral neuropathy include patient history and course of disease, electrophysiological tests, laboratory tests, cerebrospinal fluid analysis and nerve biopsy. Not all different methods need to be employed to diagnose peripheral neuropathy though. It depends on the symptoms and patient history. About 30% of all peripheral neuropathy cases remain without identifiable cause.
What does this mean with regard to a prognosis for patients with peripheral neuropathy. Luckily, in most cases peripheral neuropathy is not life-threatening. Only if the autonomous nerves are affected that regulate the heartbeat or breathing, peripheral neuropathy can be lethal. However, depending on severity of the disease, quality of life may be drastically reduced.
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