Last updated date: 10-Feb-2023

Originally Written in English

All you need to know about Peripheral Neuropathy

    Peripheral Neuropathy

    If you are a doctor or a medical student, you must know a lot about the great and mighty nervous system.

    Of all the body organs and body parts, still, the brain, or the nervous system in general, is the most mysterious and fascinating organ.

    No matter how much you learn about it, there is always more to learn and discover.

    But what about those who didn't study medicine or neurology? 

    We studied a bit about the brain and nervous system in high school.

    But, as we said, there is always more to learn and understand about the brain.

    The brain and nervous system are not our focus in this article. In fact, our article focuses on peripheral neuropathy.

    However, if we want to know more about peripheral neuropathy, first, we need to understand how neurons work.

    And if we are to understand how neurons work, we should as well understand the neurons and nerves connections with the brain and the other parts of the nervous system.


    And so, let's talk about the brain and nervous system.

    The nervous system is more like electric cables and wires.

    Just like the electricity system consists of cables, wires and control units, the nervous system is a complex network of cells and nerves that carry messages from and to the brain, the control unit, spinal cord, and other parts of the body including cells, glands, and muscles all over the body. The nervous system is the command system of the body. It literally controls everything; movements, thoughts, and automatic responses to the environment around you.

    Besides, it controls the other body systems and processes such as digestion, breathing and sexual development.

    In fact, it controls every aspect of our health, including:

    • Thoughts.
    • Memories.
    • Learning and feelings.
    • Movements such as balance and coordination.
    • Senses and interpretation of what you see, hear or even taste.
    • Healing.
    • Ageing.
    • Sleep.
    • Responses to stressful situations.
    • Heartbeat and breathing patterns. 
    • Different body processes.


    When we say the term "Nervous system" we mean both the central nervous system and the peripheral nervous system.

    So, what is the difference between the central nervous system and the peripheral nervous system? 

    Briefly, the central nervous system consists of the brain and spinal cord while the peripheral nervous system consists of somatic and autonomic nervous systems. 

    But what does that mean? 

    Let's talk about each system in detail.

    And let's start with the control unit, the central nervous system.

    The central nervous system is divided into two major parts: the brain and the spinal cord.


    The Brain

    We all know where the brain is in our bodies, it lies within its bony cover, the skull.

    It consists of four main parts: 

    • The brain stem.
    • The cerebrum.
    • The cerebellum.
    • The diencephalon.

    The brain weighs approximately 1.3- 1.4 kg. It consists of nerve cells called the neurons and supporting cells called the glia.

    The brain also consists of two types of matter: grey matter and white matter.

    That's why if you ever see a photo of a cut section of the brain, you will find two different areas with two different colors.

    The grey matter contains cell bodies of neurons and neuroglia. It is responsible for receiving and storing different impulses.

    White matter, on the other hand, consists of the nerve fibers, or also known as axons. It is responsible for carrying impulses to and from the grey matter of the cell bodies.


    The brain stem

    It is the part of the brain that lies between the pons and the spinal cord. It is about one inch long. It is also called "medulla oblongata".


    The cerebrum, however, is the big bulk of the brain. It is supported by the brain stem.

    You might wonder, what is the cerebrum? 

    The cerebrum is, actually, the two hemispheres we all know.

    Each hemisphere of them controls the activities of the opposite part of the body. 

    Each hemisphere is subdivided into four lobes:

    • Frontal lobe.
    • Temporal lobe.
    • Parietal lobe.
    • Occipital lobe.


    The cerebellum is located behind and below the cerebrum.


    As for the diencephalon, it is the part of the brain that contains the thalamus and hypothalamus.

    • The thalamus is a small structure within the brain located just above the brainstem. It has many essential roles in human physiology. It consists of different nuclei, each one is responsible for a specific role, ranging from relaying sensory and motor impulses and signals as well as control of alertness and consciousness.
    • The hypothalamus, however, is the part of the brain responsible for controlling many bodily functions such as secreting hormones that stimulate the pituitary gland to release its different hormones.

    Although it is very small, it is crucial because it controls many vital functions such as growth and sleep.


    Other parts of the brain include the midbrain and pons.

    The midbrain represents a conduction pathway to and from lower and higher centers.

    The pons acts as a pathway to higher structures. It conducts the signals between the medulla and higher centers of the brain.


    What about the other component of the central nervous system? The spinal cord? 

    The spinal cord is the long tube-like structure that lies within the spinal canal of the vertebral column. It is about 43 cm long in adult women and about 45 cm long in adult men. It weighs about 35 to 40 grams.

    It extends from the brain down to the spinal canal.

    It is composed of 31 segments. A pair of spinal nerves come out of each segment.

    The region from which the spinal nerves emerge is called the spinal segment. The spinal cord has both types of nerves: motor and sensory.

    In addition to the brain and spinal cord, the central nervous system has other parts.

    The meninges, for example, the three layers of membranes that cover the brain and the spinal cord, are considered parts of the central nervous system. There are three layers of meninges. The outermost layer is called the dura mater. The middle layer is known as the arachnoid mater, while the innermost layer is called the pia mater. 

    The dura is the toughest layer while the pia mater is the thinnest and superfine layer.

    All three of them offer protection for the brain and the spinal cord because they act as a barrier against bacteria and other microorganisms. 


    Another part of the central nervous system is cerebrospinal fluid (CSF). It is the clear colorless fluid that circulates around the brain and the spinal cord. It cushions the brain and the spinal cord from injury because it acts as a shock absorbent. It also serves as a nutrient delivery system and waste removal system for the brain. The cerebrospinal fluid is made continuously in specific areas of the brain known as the ventricles and is later absorbed by the bloodstream.


    The main unit of the nervous system is the neuron.


    What is the Neuron?


    It is the basic unit of the nervous system. It is a specialized type of cell that conducts, receives and transmits electrochemical nerve impulses and signals.

    The typical neuron has a cell body and a long arm that conducts signals from one body part to another.

    Different parts of the neuron include:

    • The cell body. It is like any other cell body with a nucleus at the center that represents the control center of the cell.
    • Dendrites. These are several branches and thick extensions that emerge from the cell body and appear like cables. Not all neurons have many dendrites. The exception is the sensory neuron that has a single long dendrite instead of many branches of dendrites. Motor neurons, on the other hand, have many thick dendrites. The dendrites' main function is to conduct electrical impulses to the cell body.
    • Axon. It is a long thick arm that carries the electrical impulses away from the cell body. There is only one axon per neuron. Sometimes it is coated by a myelin sheath and sometimes it is not.


    What is a Myelin Sheath?

    Some neurons are covered with the myelin sheath, or also known as Schwann cells.

    They are present as white segmented coverings around the axon and dendrites of many peripheral neurons.

    These coverings are continuous along the whole length of axon and dendrites except at the nodes of Ranvier and the points of termination.

    Schwann cells have a layer called the neurilemma layer. This layer has nuclei in its cells and it allows the nerve to regenerate if any damage happens.

    But not all the nerves have this neurilemma layer, for instance, nerves of the brain and spinal cord don't have neurilemma and that's why they can't recover from damage.

    So, apparently, there are multiple types of neurons.


    What are the types of Neurons? 

    Classification of the neurons depends on their function and structure.

    According to the neuron structure, neurons can be classified to: 

    • Unipolar. These are the neurons that have one process that extends from the cell body. This one process divides with one part acting as an axon and functioning as a dendrite. This type of neuron is found in the spinal cord.
    • Bipolar. These are the neurons that have one axon and one dendrite. This type of neuron is found in special senses such as the retina of the eye, the inner ear and the olfactory/smell area.
    • Multipolar. These are the neurons that have one axon and multiple dendrites. They are also common in the brain and spinal cord.


    Now it is time to talk about the peripheral nervous system.

    It is made up of:

    • Somatic nervous system. It is the nervous system that consists of peripheral nerves that carry sensations or sensory information from distant organs and body parts to the central nervous system. It also has some motor nerve fibers that take signals and orders of movement and necessary actions from the brain to distant skeletal muscles. To understand its function well, let's have a look at this example. When the hand touches a hot object, the sensory nerves carry information about the heat to the brain, which, consequently, tells the muscles of the hand to withdraw immediately via the motor neurons. When you look at this process, it seems like a lot of work, but, luckily, it takes less than a second.
    • Autonomic nervous system. It consists of three main parts: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system. It mainly controls the nerves of the body's inner organs. In other words, it controls the functions over which the human has no conscious control such as the heartbeat, digestion and breathing. The nerves of the autonomic nervous system control the involuntary muscles of the internal organs such as the muscle of the heart.

    The peripheral nervous system is as important as the central nervous system. They are equally vital and the body can't function effectively without any of them.


    What happens if any damage happens to the nerves outside the brain or the spinal cord?

    In this case weakness, numbness and pain occur. It is a condition called "Peripheral neuropathy", and it is the main point of this article.


    What is Peripheral Neuropathy?

    It is a disorder of the peripheral nerves.

    This term generally describes many conditions that cause damage to the peripheral nerves.

    As we mentioned, it often causes weakness, numbness and pain in the feet and hands. It can also affect other body functions.

    It happens when damage happens to the nerve cells of the peripheral nerves. This damage, thus, disrupts the way the nerve cells communicate with each other.

    Neuropathy can affect one nerve or nerve type and, in this case, it is called "Mononeuropathy", such as carpal tunnel syndrome. It can also affect a combination of nerves in a limited area and it is called "Multifocal neuropathy", or it can affect many peripheral nerves throughout the body and it is called "polyneuropathy".


    What does neuropathy feel like? What are the symptoms of neuropathy?

    Symptoms of neuropathy

    The most commonly reported feelings and sensations from neuropathy patients are numbness, tingling like pins and needles and weakness in the affected area of the body.

    Other sensations include:

    • Sharp pain.
    • Lightning-like pain.
    • Burning pain.
    • Throbbing pain.
    • Stabbing pain.
    • Pain in activities that shouldn't be painful such as pain in the feet when putting weight in them or pain when they are under a blanket.

    Symptoms of neuropathy depend on the type of nerve that is affected.

    For example, the previous sensation we mentioned would happen if sensory nerves are affected. Extreme sensitivity to touch also happens when sensory nerves are affected. Another strange feeling patients would feel is if they are wearing gloves or socks when they are not.


    So, when motor nerves are affected, symptoms include:

    • Lack of coordination and falling.
    • Muscle weakness.
    • Paralysis.
    • Muscle twitching, spasms and cramps.
    • Loss of muscle control.
    • Loss of muscle tone.
    • Dropping things out of the hands.
    • Unintentional weight loss due to atrophy of the muscles.
    • If autonomic nerves are affected, symptoms include:
    • Excessive sweating or not being able to sweat at all.
    • Heat intolerance.
    • Bowel or bladder problems.
    • Digestive problems.
    • Sudden drops of blood pressure, causing dizziness and fainting.
    • Sexual function problems.


    What are the causes of peripheral neuropathy?

    Because neuropathy happens when there is nerve damage, it can happen due to several causes.

    Health conditions and diseases that can cause neuropathy include:

    • Autoimmune disorders. These include Sjogren's syndrome, lupus rheumatoid arthritis, Guillain-Barre syndrome, vasculitis and chronic inflammatory demyelinating polyneuropathy.
    • Infections. Some types of infection cause damage to the nerves such as Chickenpox, shingles, HIV, Lyme disease, herpes, syphilis, West Nile virus, hepatitis C and Epstein-Barr virus.
    • Diabetes. This is the most common cause. Of all diabetics, more than half will develop some type of neuropathy.
    • Inherited disorders. Some disorders are a hereditary type of neuropathy such as Charcot-Marie-Tooth disease.
    • Tumors. If a tumor, either benign/ non-cancerous or malignant/ cancerous, develops on a nerve, it will press on the nerve and cause damage. Besides, polyneuropathy can occur when cancer-related to the body's immune response develops. In this case, it is called "Paraneoplastic syndrome”, a form of a degenerative disorder.
    • Bone marrow disorders. Some types of bone marrow cancer such as myeloma, lymphoma, or amyloidosis can induce the presence of abnormal proteins in the blood, a condition known as (Monoclonal gammopathies).
    • Other health conditions. Some diseases can also induce neuropathy such as kidney disorders, liver disorders, hypothyroidism and cancers.
    • Trauma. Injuries that occur due to falls, car accidents, fractures and sports activities can result in neuropathy. The compression of nerves due to friction or narrowing of the space in which the nerve runs can cause neuropathy.
    • Poisons and medications. Some medications can cause neuropathy such as antibiotics, some anti seizures and some HIV medications. Cancer chemotherapy and radiation can also damage peripheral nerves. In addition to chemotherapy, exposure to toxic substances such as lead, mercury and industrial chemicals especially solvents can cause severe damage to the peripheral nerves.
    • Vascular disorders. Neuropathy usually occurs when blood supply to the arms and feet is decreased or slowed by inflammation. But what is the relation between decreased blood flow and neuropathy? When the blood flow is decreased, nerve cells become deprived of oxygen and become damaged. Sooner or later these deprived nerve cells will die due to a lack of oxygen and nutrients. Vascular problems can happen due to blood clots, vasculitis or diabetes.
    • Abnormal vitamin levels. Proper levels of some vitamins such as vitamins E, B1, B6, B12 and niacin are essential for healthy nerve function. Alcoholism is one of the most commonly known causes of neuropathy because chronic alcoholism causes a lack of thiamine and other essential vitamins needed for nerve function. Besides, alcohol can be directly toxic and damaging to the peripheral nerves.
    • No known cause. Some reported cases of neuropathy are still vague and happen with no recognizable causes.


    How is Neuropathy diagnosed?


    When a patient complains of the previous symptoms, the first step in their evaluation will be a physical examination.

    The doctor will conduct a thorough history and physical examination.

    The doctor will also ask about the current and past medications, exposure to toxic substances, occupation, family history of neurological diseases, alcohol abuse and history of trauma.

    The next step is conducting some neurological examinations.

    Doctors in similar situations will need to check the reflexes, coordination, balance, muscle strength and tone. They will also make sure that sensations are intact.

    Other investigations include: 

    • Blood work and imaging tests.
    • Genetic testing. It is done when the doctor suspects a neurological hereditary disease.
    • Nerve conduction studies.
    • Needle electromyography.
    • Tissue biopsies.
    • QSART test; measures the body's ability to sweat.


    How is neuropathy treated?

    Because there are many reasons why patients get neuropathy, the most important step is to identify the underlying cause and treat it.

    If there is a medical condition such as diabetes and infections, it should be controlled or treated first.

    Many types of neuropathies are easily treated and even cured. Unfortunately, not all cases of neuropathy are cured, and in this case, treatment aims to control the symptoms and prevent further nerve damage.

    Lines of neuropathy treatment are:

    • Medications. They are used to control the pain by adjusting pain signaling pathways.
    • Physical therapy. It is all about focused exercises and massages that help increase the strength of the muscles and improve motion.
    • Occupational therapy. It helps patients to cope with their losses by teaching them new skills.
    • Surgery. It is only available for patients with compression-related neuropathy such as herniated disks and carpal tunnel syndrome.
    • Mechanical aids. Some braces and specially designed shoes, casts and splints are specifically made for neurological patients. They help reduce the pain by supporting and keeping the affected nerves in the right alignment.
    • Better nutrition. Eating a healthier diet and getting enough amounts of the important vitamins significantly help in improving nerve functions.
    • Healthy lifestyle and habits. Adopting healthy habits like exercising, quitting smoking, maintaining a healthy weight and limiting alcohol intake can boost overall health and improve nerve functions.