Nerve injury
Encyclopedia
Nerve injury is injury
to nervous tissue
. There is no single classification system that can describe all the many variations of nerve injury. Most systems attempt to correlate the degree of injury with symptoms, pathology and prognosis. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve fiber injury and whether there is continuity of the nerve.
). There is a temporary loss of function which is reversible within hours to months of the injury (the average is 6–9 weeks). Wallerian degeneration
does not occur, so recovery does not involve actual regeneration. There is frequently greater involvement of motor than sensory function with autonomic function being retained. In electrodiagnostic testing with nerve conduction studies, there is a normal compound motor action potential amplitude distal to the lesion at day 10, and this indicates a diagnosis of mild neuropraxia instead of axonotmesis or neurotmesis.
al axon
, but with maintenance of the myelin sheath. This type of nerve damage may cause paralysis
of the motor, sensory, and autonomic
. Mainly seen in crush injury.
If the force creating the nerve damage is removed in a timely fashion, the axon may regenerate, leading to recovery. Electrically, the nerve shows rapid and complete degeneration, with loss of voluntary motor units. Regeneration of the motor end plates will occur, as long as the endoneural tubules are intact.
Axonotmesis involves loss of the relative continuity of the axon and its covering of myelin
, but preservation of the connective tissue
framework of the nerve ( the encapsulating tissue, the epineurium and perineurium, are preserved ). Because axonal continuity is lost, Wallerian degeneration
occurs. Electromyography
( EMG ) performed 2 to 4 weeks later shows fibrillations and denervation potentials in musculature distal to the injury site. Loss in both motor and sensory spines is more complete with axonotmesis than with neurapraxia, and recovery occurs only through regenerations of the axons, a process requiring time.
Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia, but can also occur when the nerve is stretched (without damage to the epineurium). There is usually an element of retrograde proximal degeneration of the axon, and for regeneration to occur, this loss must first be overcome. The regeneration fibers must cross the injury site and regeneration through the proximal or retrograde area of degeneration may require several weeks. Then the neuritis tip progresses down the distal site, such as the wrist or hand. Proximal lesion may grow distally as fast as 2 to 3 mm per day and distal lesion as slowly as 1.5 mm per day. Regeneration occurs over weeks to years.
. Not only the axon, but the encapsulating connective tissue lose their continuity. The last (extreme) degree of neurotmesis is transsection, but most neurotmetic injuries do not produce gross loss of continuity of the nerve but rather internal disruption of the architecture of the nerve sufficient to involve perineurium and endoneuruim as well as axons and their covering. Denervation changes recorded by EMG are the same as those seen with axonotmetic injury. There is a complete loss of motor, sensory and autonomic
function. If the nerve has been completely divided, axonal regeneration causes a neuroma
to form in the proximal stump. For neurotmesis, it is better to use a new more complete classification called the Sunderland System.
, generation of new neuron
s, glia, axon
s, myelin
or synapse
s. Neuroregeneration differs between the Peripheral Nervous System
(PNS) and the Central Nervous System
(CNS) by the functional mechanisms and especially, the extent and speed.
Surgery can be done in case a peripheral nerve has become cut or otherwise divided. Recovery of a nerve after surgical repair depends mainly on the age of the patient. Young children can recover close-to-normal nerve function. In contrast, a patient over 60 years old with a cut nerve in the hand would expect to recover only protective sensation, that is, the ability to distinguish hot/cold or sharp/dull. Many other factors also affect nerve recovery.
In contrast, repair after damage to the central nervous system is limited.
Injury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...
to nervous tissue
Nervous tissue
Nervous tissue is one of four major classes of vertebrate tissue.Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions...
. There is no single classification system that can describe all the many variations of nerve injury. Most systems attempt to correlate the degree of injury with symptoms, pathology and prognosis. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve fiber injury and whether there is continuity of the nerve.
Neurapraxia
This is the least severe form of nerve injury, with complete recovery. In this case, the actual structure of the nerve remains intact, but there is an interruption in conduction of the impulse down the nerve fiber. Most commonly, this involves compression of the nerve or disruption to the blood supply (ischemiaIschemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
). There is a temporary loss of function which is reversible within hours to months of the injury (the average is 6–9 weeks). Wallerian degeneration
Wallerian degeneration
Wallerian degeneration is a process that results when a nerve fiber is cut or crushed, in which the part of the axon separated from the neuron's cell body degenerates distal to the injury. This is also known as anterograde degeneration, or orthograde degeneration...
does not occur, so recovery does not involve actual regeneration. There is frequently greater involvement of motor than sensory function with autonomic function being retained. In electrodiagnostic testing with nerve conduction studies, there is a normal compound motor action potential amplitude distal to the lesion at day 10, and this indicates a diagnosis of mild neuropraxia instead of axonotmesis or neurotmesis.
Axonotmesis
This is a more severe nerve injury with disruption of the neuronNeuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
al axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
, but with maintenance of the myelin sheath. This type of nerve damage may cause paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
of the motor, sensory, and autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. Mainly seen in crush injury.
If the force creating the nerve damage is removed in a timely fashion, the axon may regenerate, leading to recovery. Electrically, the nerve shows rapid and complete degeneration, with loss of voluntary motor units. Regeneration of the motor end plates will occur, as long as the endoneural tubules are intact.
Axonotmesis involves loss of the relative continuity of the axon and its covering of myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
, but preservation of the connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
framework of the nerve ( the encapsulating tissue, the epineurium and perineurium, are preserved ). Because axonal continuity is lost, Wallerian degeneration
Wallerian degeneration
Wallerian degeneration is a process that results when a nerve fiber is cut or crushed, in which the part of the axon separated from the neuron's cell body degenerates distal to the injury. This is also known as anterograde degeneration, or orthograde degeneration...
occurs. Electromyography
Electromyography
Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...
( EMG ) performed 2 to 4 weeks later shows fibrillations and denervation potentials in musculature distal to the injury site. Loss in both motor and sensory spines is more complete with axonotmesis than with neurapraxia, and recovery occurs only through regenerations of the axons, a process requiring time.
Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia, but can also occur when the nerve is stretched (without damage to the epineurium). There is usually an element of retrograde proximal degeneration of the axon, and for regeneration to occur, this loss must first be overcome. The regeneration fibers must cross the injury site and regeneration through the proximal or retrograde area of degeneration may require several weeks. Then the neuritis tip progresses down the distal site, such as the wrist or hand. Proximal lesion may grow distally as fast as 2 to 3 mm per day and distal lesion as slowly as 1.5 mm per day. Regeneration occurs over weeks to years.
Neurotmesis
Neurotmesis is the most severe lesion with potential of recovering. It occurs on severe contusion, stretch, laceration, or Local Anesthetic ToxicityLocal anesthetic toxicity
While generally safe, local anesthetic agents can be toxic if used in excessive doses or administered improperly. Even when administered properly, patients may still experience unintended reactions to local anesthetics....
. Not only the axon, but the encapsulating connective tissue lose their continuity. The last (extreme) degree of neurotmesis is transsection, but most neurotmetic injuries do not produce gross loss of continuity of the nerve but rather internal disruption of the architecture of the nerve sufficient to involve perineurium and endoneuruim as well as axons and their covering. Denervation changes recorded by EMG are the same as those seen with axonotmetic injury. There is a complete loss of motor, sensory and autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
function. If the nerve has been completely divided, axonal regeneration causes a neuroma
Traumatic neuroma
A traumatic neuroma is a type of neuroma which results from trauma to a nerve, usually during a surgical procedure. The most common oral locations are on the tongue and near the mental foramen of the mouth. They are relatively rare on the head and neck.It is also known as "pseudoneuroma"....
to form in the proximal stump. For neurotmesis, it is better to use a new more complete classification called the Sunderland System.
Regeneration
Physiological mechanisms or neuroregeneration may include remyelinationRemyelination
Remyelination is a term for the re-generation of the nerve's myelin sheath, damaged in many diseases such as multiple sclerosis and the leukodystrophies. Remyelination is a subject of active medical research.-External links:**...
, generation of new neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s, glia, axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s, myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
or synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
s. Neuroregeneration differs between the Peripheral Nervous System
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
(PNS) and the Central Nervous System
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
(CNS) by the functional mechanisms and especially, the extent and speed.
Surgery can be done in case a peripheral nerve has become cut or otherwise divided. Recovery of a nerve after surgical repair depends mainly on the age of the patient. Young children can recover close-to-normal nerve function. In contrast, a patient over 60 years old with a cut nerve in the hand would expect to recover only protective sensation, that is, the ability to distinguish hot/cold or sharp/dull. Many other factors also affect nerve recovery.
In contrast, repair after damage to the central nervous system is limited.
See also
- Brain injury (disambiguation)
- Neuroregeneration
- Peripheral nerve
- Peripheral nerve injuryPeripheral nerve injuryPeripheral nerve damage is categorized in the Seddon classification based on the extent of damage to both the nerve and the surrounding connective tissue since the nervous system is characterized by dependence of neurons on their supporting glia. Unlike in the central nervous system, regeneration...
- Seddon's classification
- Wallerian degenerationWallerian degenerationWallerian degeneration is a process that results when a nerve fiber is cut or crushed, in which the part of the axon separated from the neuron's cell body degenerates distal to the injury. This is also known as anterograde degeneration, or orthograde degeneration...