Neuropraxia

What is Neuropraxia (Nerve Injury)?

In the majority of the cases, the injury to the nerve appears as a direct result of acute trauma. The peripheral nerves present the highest risk for injuries, especially in situations of blunt force or bone fractures. These are the nerves that are found in the extremities, more specifically outside the spinal cord and brain. They can also be easily injured when it comes to penetrating wounds, lacerations or stretch excessively (as a result of trauma as well). It is important to understand that the nerve regeneration is a gradual process, lasting sometimes for several months. In general, the rapidity with which the nerve regenerates depends on how extensive the nerve damage actually was. The type of injury also influences the recovery process.

Nerve Structure and Types

Each nerve that is part of the peripheral system is constituted out of Schwann cells and axons. According to the presence of an outer insulating layer, there are two types of nerves: myelinated and unmyelinated. In the myelinated nerves, the Schwann cells cover each axon (sheath formation). When it comes to the unmyelinated nerves, the Schwann cells cover the grouped axons. A second layer comes to cover the sheath-protected axons, this being known as the endoneurium.

The nerve fascicles are constituted out of endoneurial tubes, with each fascicle being further covered by tissue (perineurium). The group of nerve fascicles is covered by an additional layer of tissue, which is known as the epineurium. Each nerve receives its own blood supply through a complex system of blood vessels (vasa nervorum).

The human body has three main types of nerves:

Autonomic nerves

• Control both involuntary and partially voluntary activities
• Are involved in the regulation of physiological processes (heart rate, blood pressure, temperature, digestion etc.)

Motor nerves

• Movement control
• Are responsible for the transmitting of information from the brain and the spinal cord to the corresponding muscles

Sensory nerves

• Responsible for transmitting the information from the skin and muscles to the brain and spinal cord
• Information is related to sensory input (such as the pain sensation).

Types of Nerve Injury

According to the specialists in the field, the nerve injuries can be classified into three main categories:

Neuropraxia

• Least severe
• Complete block of nerve transmission (nerve fibers intact)
• Axon + protective sheath intact as well
• Main cause – fracture or dislocation (sudden stretching of the nerve)
• Rare situations – blunt injury, prolonged pressure on the nerve
• Recovers spontaneously (depending on the extent of the damage, from a couple of weeks to several months)

Axonotmesis

• Most common causes – traction injury, crush injury
• Nerve sheath intact, axons divided
• Complete loss of motor function (signal nerve-muscle impaired)
• The nerve can also lose its sensory and autonomic function
• Prolonged recovery (from a couple of months to years)

Neurotmesis

• Both axons and sheath are severed (partial or complete)
• Most severe form
• Clean cut – best chance for immediate repair (thus, a faster recovery is guaranteed).

How do Nerve injuries occur? (Mechanisms)

There are several injury mechanisms through which the nerve damage can occur:

Mechanical injury

• Main cause – external pressure – nerve compression – damage
• Compression can be caused by adjacent structures
• Trauma is often the main cause behind the mechanical injury (car accident, falling from a certain height etc.)
• Crush injuries and bone fractures can compress the nerves as well, with associated damage
• Other cause of mechanical injuries are:
  • Hematoma
  • Blunt force
  • Compartment syndrome (the swelling of the tissues causes nerve compression, with the nerve being damaged and the blood supply to the nerve cut as well)

Laceration injury

• Blunt/penetrating wound
• Irregular pattern of nerve damage
• The nerve can be cut (partial or complete; not clean, as in cut injuries)

Penetrating injury

• Partial/complete severance of the nerve
• Stab wound/cut wound (sharp object)

Stretch injury

• Main cause – fracture or dislocation
• Sudden stretch of the nerve occurs at the same time with the fracture or dislocation
• Half of shoulder dislocations are accompanied by nerve injuries of this kind
• The peripheral nerves can be accidentally stretched during certain surgical intervention

Direct injury

• High-velocity trauma
• Most common – motor accident, gunshot wound (ballistic injury)
• May also be caused by a displaced bone fracture
• Violent traction (if this is the case, the nerve can be severely damaged, with partial or complete severance).

Other causes of nerve injuries (non-traumatic)

It is possible that peripheral nerve damage occurs as a direct result of non-traumatic health problems, such as:

• Diabetes
  • 1 in 4 people diagnosed with diabetes present some form of nerve damage
  • This condition is known as diabetic neuropathy – serious complication of diabetes, can lead to nerve injury in all the different types of nerves
  • Most common – impairment of sensory nerves (burning sensation or numbness present among the other symptoms)
• Autoimmune diseases
  • Multiple sclerosis
  • Guillain-Barre syndrome
  • Myasthenia gravis
  • Lupus
  • Inflammatory bowel disease
• Cancer
  • Primary/secondary neoplastic growth (metastases)
  • The treatment for cancer can also lead to nerve injury (chemotherapy, radiation)
• Medication (nerve damage – side effect)
  • Chemotherapy drugs (for cancer patients)
  • Retroviral medication (for HIV/AIDS patient)
• Ingestion of toxic substances (accidental)
  • Lead
  • Arsenic
  • Mercury
• Motor neuron diseases
  • Amyotrophic lateral sclerosis (Lou Gehrig’s disease) – progressive nerve damage
• Nutritional deficiency
  • Vitamin B16, B12 deficiency (muscular weakness or burning sensation, due to the associated nerve damage)
  • Other causes of nutritional deficiencies – alcohol abuse, gastric surgery (post-operative complication)
• Infectious disease
  • Lyme disease
  • Viral infection (herpes virus)
  • HIV
  • Hepatitis (hepatitis C virus).

Neuropraxia Signs and Symptoms

These are the most common signs and symptoms of nerve injuries:

• Loss of normal function (acute injury)
• Impairment of motor function (or complete loss)
• Impairment of sensory function (or complete loss)
• Weakness or paralysis of the muscles innervated by the damaged nerve (depending on the extent of the damage); because of the loss of function, gradual atrophy can occur at the level of the muscles
• Loss of sensation or abnormal sensation (such as paresthesia, numbness, tingling or burning sensation) in the territory covered by the damaged nerve; in many cases, fasciculation is encountered at the level of the muscles (also known as twitching – sign of impaired innervation)
• Pain on the trajectory of the nerve (sensory function impaired, sometimes described as the “needles and pins” sensation)
• Excessive sweating (sign of sensory impairment)
• Bladder and bowel dysfunction (sign that the nerves of the spinal cord have been affected; the sexual function might be impaired or lost as well).

Healing Process of Injured Nerve

When it comes to nerve injuries, the healing process is gradual and it can extend over the course of several months (provided that the nerve has not been severed). In the situation that the nerve has been damaged beyond repair, a complete recovery cannot be expected. There are some nerves that never recover from the suffered injury, losing their function completely.

The human body is a machine made to function to perfection and, looking at the healing process of the nerve injuries, it is easy to agree with this statement. After a nerve has been injured, it first goes through what is known as a process of degeneration. This means that the damaged segment of the nerve is going to be consumed by specialized cells, so as the regeneration process can begin. The nerve growth factor is responsible for the start of this process but this is not the only key element of the process. According to the research made in the field, it seems that there are other growth factors, not to mention cytokines, which play an essential part in the recovery process.

After the degeneration process has been completed, the regeneration stage will begin (from the proximal end of the nerve, at the injury site). The regeneration progresses on a gradual but slow basis, at a rate of approximately 1 mm/day. The longer the segment of the nerve that has been affected, the longer the recovery is going to be. Moreover, the closer the damaged nerve is to the muscle it innervates, the faster and better the recovery is going to be. It is possible that the regeneration process does not follow a healthy course, a modification which can lead to abnormal connections. This means that the patient will suffer from irregular movement patterns, not to mention a wide array of abnormal sensations. It is said that the muscle innervated by the damaged nerve will retain its normal functioning, provided that the regeneration process is completed within 18 months after the injury has occurred.

Treatment of Nerve Injuries

From the start, it should be mentioned that not all nerve injuries can be cured. Depending on the regeneration process, it is possible to reduce the symptoms experienced by patients who have suffered from severe nerve injuries. In the situation that the nerve damage is progressive, it is just as important to keep the underlying condition under control. In this way, the permanent damage to the respective nerves can be easily prevented.

These are the most common measures that can be taken for patients who have suffered from different types of nerve injuries:

• Diabetes
  • Medication to keep the blood sugar levels under control
  • Change of diet
• Nutritional deficiency
  • More fresh fruits and vegetables included in the diet
  • Vitamin supplements
• Replacing the medication with alternative drugs that do not have such side-effects
• Surgical intervention
  • Remove the structure that compresses the nerve and repair the damaged fibers (if possible)
• Medication to keep the immune system under control (in case of autoimmune conditions)
• Symptomatic medication
  • Analgesics (pain relief)
  • Tricyclic antidepressant (may help the patient to cope with his/her condition)
  • Anti-seizure medication (can improve the coping mechanisms)
• Alternative medicine
  • Hypnosis
  • Acupuncture
  • Biofeedback
  • Meditation

Physical therapy for Neuropraxia

Physical therapy is essential for the healthy recovery of different nerve injuries. The earlier physical therapy is started, the better the prognosis will be for the respective patient. At the beginning of the therapy, the patient will be prevented from active movements. Instead, the physical therapist will concentrated on passive movements, so as to maintain a normal range of motion and prevent the atrophy of the muscles innervated by the damaged nerve. As the nerve regeneration occurs, the physical therapist will make the transition towards more activity, performing the movements that are passive-active. Once the patient is more confident in his/her abilities, he/she can move on to the active movements. The physical therapist can work side by side with the occupational therapist, the latter being involved in the rehabilitation of the fine motor skills.