What Is Nerve Injury?

Introduction and types of nerve injury

To understand what a nerve injury is, it is first important to understand what a nerve is. Nerves are like the wires of the telephone in the body. They send and carry messages to the brain and the rest of the body. While some nerves carry signals from the brain to the muscles to make the body move, other nerves send messages about stimuli such as pain, temperature, and pressure to the brain.¹

Nerves are very fragile and can be damaged through pressure, cutting and stretching, so an injury to the nerve can stop the nerve from sending signalling messages to and from the brain. This can lead to the muscles stopping working efficiently and having a sense of loss of feeling. This damage, depending on the severity and its location, can harm someone's quality of life and their ability to function.¹

There are 2 types of nerve injury:

• Peripheral Nerve Injury: Damage to the peripheral nerves, which send signals from the Central Nervous System (Brain and Spinal cord) to the internal organs, muscles and sensory tissues, which control the basic functions needed to live.²
• Central Nervous System Injury: Damage to the nerves of the spinal cord. These injuries have a significantly worse effect than peripheral nerve injuries. Depending on where the injury is, disability is likely to follow these injuries, which may go as far as paralysis.³

Anatomy of nerves

Nerves are bunches of neuronal cells which are responsible for taking and sending information and signals to various parts of the body.

Structure of neurons

The structure of a neuron can be broken down into the following:^1,4

• Cell Body: The headquarters of the neuronal cell. The cell body generates energy for the rest of the cell, maintains its structure and holds the genetic material of the cell.
• Dendrites: These are long, spindly projections from the cell body that look like roots spreading out. These allow for the neuron to receive signals from other nearby neurons.
• Myelin Sheath: the insulation layer that forms around the nerves and allows the electrical impulses to transmit faster through the neurons.
• Axons: long, tail structure which joins the cell body, in addition to myelin, helps to send electrical signals.

Neurons may differ from each other depending on where they are in the body as well as what role they conduct. For example, some neuronal cells have more than one axon, while others have one axon but lots of dendrites.

Nerve classification

• Sensory Neurons: receive and interpret the sensory signals through input from the environment.⁵
• Motor Neurons send signals from the brain to the muscles for movement, speech, swallowing, and breathing.⁵
• Inter Neurons: these are found in the central nervous system, only the brain and the spinal cord, and they help to transit signals between other neurons.⁵

Causes of nerve injury

There are several ways that nerve injuries can be caused, but they all lead to neurons having difficulty sending or receiving signals. They can be spontaneous from traumatic causes, such as from a car accident or a fall. These can cause nerves to stretch, crush, compress or be cut, causing damage to the nerve. 

Other ways could be by non-traumatic causes, such as infection, medical conditions and autoimmune disorders. A prominent syndrome is Carpal tunnel syndrome, which affects the wrists, causing numbness and tingling pain in the fingers or hands. Lupus is an autoimmune disease that can damage neurons by causing inflammation of the tissues and neighbouring neurons. 

Signs and symptoms of nerve injury

If a nerve is injured or damaged, then there can be a range of different symptoms that a person may experience. They can depend on the location or the type of nerve that was affected, as well as if it is a peripheral or CNS nerve injury. People may also experience symptoms and signs that suggest two or more types of nerve damage. For example, you experience burning and weakness at the same time. The way nerve injuries affect people can be broken down into three categories:⁶

Sensory symptoms:

These symptoms cover sensations linked to senses such as feel and include:

• Numbness
• Tingling
• Pain
• Sensitivity
• Burning
• Positional awareness

Motor symptoms:

These symptoms are linked to movement and the muscles. They can include:

• Weakness
• Muscle Atrophy
• Paralysis
• Twitching

Autonomic symptoms:

Autonomic symptoms are associated with bodily functions that you do without thinking about, such as breathing, your heart beating or the digestion of food. These symptoms include:

• Excessive or little sweating
• Angina/ heart attack
• Lightheadedness
• Constipation
• Bladder dysfunction
• Sexual dysfunction
• Dry eyes/mouth

Diagnosis of nerve injury

Medical history and physical examination

When going for an examination, a doctor would ask about your symptoms, any injuries and your health history which will include what medication you take and other conditions you’ve been diagnosed with. During physical examination, the doctor would test the feeling in the injured limb and how well you can move different muscles. The doctor would also check if any other injuries could be associated with the injury, for instance, the bone, tendon or blood vessels.⁷

Electrophysiological tests

To find the location and the severity of the nerve damage, different tests can be done to diagnose:

• Nerve Conduction Studies: measures the function of the peripheral nerves. Shows the presence of any injury and how badly the nerves are affected. It is done by measuring how fast the electrical impulse is travelling in the nerve through electrode patches.⁶
• Electromyography (EMG): Done in conjunction with a nerve conduction study to understand the degree of damage in the nerves. It measures the muscle response and the electrical activity present in the nerve.⁸

Imaging techniques

This can help to confirm the location of the nerve damage and any affected surrounding areas.

• MRI: Locates any nerve damage which was difficult to find out through electrophysiological tests. MRI tests can show soft tissue structures and any damage to the spinal nerves. 
• Computerised tomography (CT) scans: Use a special dye that makes it easier to show structures and damage to the nerve.⁹

Blood tests

Blood tests can help check for any underlying cause of nerve damage, for example, blood tests for diabetes or vitamin B12 deficiency or if you have neuropathy. 

Treatment options for nerve injury

Conservative management

For minor nerve injuries, the nerve can heal over time and can return to function normally. However, the location and the type of nerve can determine how fast the healing process is:⁶

• Physical Therapy: Useful to keep the joints flexible until the muscles function normally and can also help to strengthen the muscles. 
• Medication: This is given to ease the pain of nerve damage as it can be uncomfortable and, in some cases, painful. 

Surgical interventions

Used for more severe nerve damage, so when the outer layer of the nerve is damaged or broken.¹⁰

• Nerve Repair: aimed to fix the nerve by repairing the insulating layer so that new fibres can form around the insulating layer.
• Nerve Grafting: uses part of a nerve from elsewhere in the body to repair the space between the nerve. This may result in a complete loss of feeling in the area from which the nerve was taken.

Recovery and prevention

For recovery, therapy is often used to keep the muscles in a normal form until the nerves recover. Depending on the nerve damage, the brain may need “re-educating” to improve feeling in the affected area. This is done via physical therapy. After a nerve repair procedure, different factors can affect the outcome. These can include age, location of the damage and the type of nerve affected. To prevent any further complications, you must take care to not burn or cut when there is no feeling in the area.⁷

Complications and long-term effects

Due to nerve damage causing neuropathy, there are several complications to the condition. In some cases an individual can improve with time if the symptoms are treated, however, in some cases the damage can be permanent or worsen with time, causing chronic pain. For example, neuropathic foot ulcers can lead to gangrene, and if left untreated, the foot could be amputated, causing a permanent disability. In rare cases, if heart nerves are affected, then a pacemaker is needed for normal heart function.¹¹

Research and advancements in nerve injury

Stem Cell Therapy can potentially be very effective in repairing spinal cord nerve injuries. The use of stem cell transplantation offers a newer promise for the future of molecular medicine.^12,13

With the current technological advances, newer research suggests the use of next-generation nerve regeneration by combining 3D printing, stem cells, and nanoscience. One area of research is looking at growing nerve cells from other types of cells within a scaffold to fix the exact dimensions of existing damaged nerve cells. The scaffold with the grown nerve cells inside could be transplanted to repair the nerve injury. Although promising, this research is still in its early stages and will take time before reaching clinical trials.¹⁴

Summary

Nerves are the messaging system of the body, which allows us to move, breathe and function normally. However, if a nerve is injured, then early detection is advisable so that proper treatment can be given. If left untreated, serious complications can affect the quality of life.

Current treatments for nerve injuries are limited to trying to prevent further damage, managing the symptoms of the damage and some surgery techniques that can help repair damaged nerves. However, these methods are limited in what they can achieve for those with severe nerve damage. Although in the early stages of research, research into stem cell treatment for nerve damage may help overcome the limitations of current therapies.