Neurotmesis

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Neurotmesis (in Greek tmesis signifies "to cut") is part of Seddon's classification scheme used to classify nerve damage. It is the most serious nerve injury in the scheme. In this type of injury, both the nerve and the nerve sheath are disrupted. While partial recovery may occur, complete recovery is impossible.

Contents

Symptoms

Symptoms of neurotmesis include but are not limited to pain, dysesthesias (uncomfortable sensations), and complete loss of sensory and motor function of the affected nerve. [1]

Anatomy

Neurotmesis occurs in the peripheral nervous system and most often in the upper-limb (arms), accounting for 73.5% of all peripheral nerve injury cases. [2] Of these cases, the ulnar nerve was most often injured. Peripheral nerves are structured so that the axons are surrounded by most often a myelinated sheath and then an endoneurium. A perineurium surrounds that and the outermost layer is considered the epineurium. [2] When injury occurs, "local vascular trauma leads to hemorrhage and edema (swelling), which results in vigorous inflammatory response resulting in scarring of the injured segment. [3] In most cases, due to the extreme nature of the injury, there is typically complete loss of function.

Mechanisms

Trauma is the most frequent cause of peripheral nerve lesions. [1] There are two classifications of trauma which include civilian trauma and military trauma. [2] Civilian trauma is most commonly caused by motor vehicle accidents but also by lacerations caused by glass, knives, fans, saw blades or fractures and occasionally sports injuries. [2] Of the civilian injuries, stretch injuries are the most common types and are considered to be a closed injury, where the tissue is unexposed. [3] Stretch injures are commonly the result of dislocation, such as a shoulder dislocation that stretches nerves. Opposite of civilian trauma, there is military trauma which most commonly results in open injuries from blasts often by bombs or improvised explosive devices. [2] Other mechanisms of injury are less common but include ischemia, thermal, electric shock, radiation, adverse reactions to certain chemotherapy medications, percussion and vibration. [2]

Diagnosis

With Seddon's classification of nerve injuries, it is often tough to identify whether a particular nerve injury is neurotmesis, or axonotmesis, which has damage to the nerve fibres but preservation of the nerve trunk. Due to the damage involved in both of these conditions they will both show paralysis of muscles that are supplied by nerves below the site of the lesion, and will have sensory deficits in accordance with the individual nerves that are damaged. [4] The only way to know for sure if a nerve injury is in fact neurotmesis is to allow for the normal progression of nerve regeneration to take place (nerves regenerate at a rate of approximately 2–4 mm/day proximal to the lesion), and if, after that time, there is still profound muscle paralysis and degeneration in these areas, then it is likely to have been a neurotmesis injury. [4]

Neurotmesis is diagnosed through clinical evaluation of symptoms, physical evaluation, and other diagnostic studies. Patients often undergo a series of muscle strength tests, sensory exam which includes feeling the sensation of light touch, pinprick, vibration, and others. [1] Other tests involved with diagnosis of nerve injury are electromyography (EMG) and nerve conduction studies (NCS). These help to distinguish upper from lower motor neuron disorder as well as diagnose primary muscle disease. [1]

Classification

Peripheral nerve injuries can be classified in two different ways. Neurotmesis is classified under the Seddon system which is defined by three grades of nerve injury. The mildest grade is referred to as neurapraxia and is characterized by a reduction or complete blockage of conduction across a segment of nerve while axonal continuity is maintained and nerve conduction is preserved. [1] These injuries are almost always reversed and a recovery takes place within days or weeks. The second classification of the Seddon system is referred to as axonotmesis which is a more severe case of peripheral nerve injury. Axonotmesis is classified by an interruption of the axons, but a preservation of the surrounding connective tissues around the axon. [1] These injuries can heal themselves at about 1mm/day, therefore resulting in recovery to be possible but at a slower rate than neurapraxia. [5] The last and most severe case of peripheral nerve injury is known as neurotmesis, which in most cases cannot be completely recovered from even with surgical repair.

The second classification of nerve injury is known as the Sunderland classification which is more complex and specific. This classification uses five different degrees of nerve injury, the first one being the least severe and the equivalent to neurapraxia and the most severe being the fifth degree and having the same classification as neurotmesis. The second through fourth degrees are dependent on the variance of axon discontinuity and are classified under Seddon's classification of axonotmesis. [2]

Treatment

The first line of treatment is often to treat the patient's pain with neuropathic drugs such as tricyclic antidepressants, serotonin reuptake inhibitors, and anticonvulsants. The second lines of drugs to treat pain are non-steroidal anti-inflammatories, tramadol, and opioids. Other techniques used to facilitate healing of the nerve and pain are either static or dynamic splinting that can both help protect the injured part as well as improve function. [2] Sometimes surgery is an option, although the prognosis is still very poor of regaining function of the affected nerve. [2] The goal of surgery is to join healthy nerve to unhealthy nerve. The most common surgical techniques include external neurolysis, end-to-end repair, nerve grafting, and nerve transfer from somewhere else in the body. [2]

Prognosis

People with neurotmesis often face a poor prognosis. They will more than likely never regain full functionality of the affected nerve, but surgical techniques do give people a better chance at regaining some function. Current research is focused on new ways to regenerate nerves and advance surgical techniques. [3] [ needs update ]

See also

Related Research Articles

Nerve Enclosed, cable-like bundle of axons in the peripheral nervous system

A nerve is an enclosed, cable-like bundle of nerve fibers in the peripheral nervous system.

Motor nerve

A motor nerve is a nerve located in the central nervous system (CNS), usually the spinal cord, that sends motor signals from the CNS to the muscles of the body. This is different from the motor neuron, which includes a cell body and branching of dendrites, while the nerve is made up of a bundle of axons. Motor nerves act as efferent nerves which carry information out from the CNS to muscles, as opposed to afferent nerves, which send signals from sensory receptors in the periphery to the CNS. Efferent nerves can also connect to glands or other organs/issues instead of muscles. In addition, there are nerves that serve as both sensory and motor nerves called mixed nerves.

Electroneuronography or electroneurography (ENoG) is a neurological non-invasive test used to study the facial nerve in cases of muscle weakness in one side of the face. The technique of electroneuronography was first used by Esslen and Fisch in 1979 to describe a technique that examines the integrity and conductivity of peripheral nerves. In modern use, ENoG is used to describe study of the facial nerve, while the term nerve conduction study is employed for other nerves.

Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact. Motor and sensory functions distal to the point of injury are completely lost over time leading to Wallerian degeneration due to ischemia, or loss of blood supply. Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia.

Neurapraxia is a disorder of the peripheral nervous system in which there is a temporary loss of motor and sensory function due to blockage of nerve conduction, usually lasting an average of six to eight weeks before full recovery. Neurapraxia is derived from the word apraxia, meaning “loss or impairment of the ability to execute complex coordinated movements without muscular or sensory impairment”.

Neuralgia is pain in the distribution of a nerve or nerves, as in intercostal neuralgia, trigeminal neuralgia, and glossopharyngeal neuralgia.

In medicine, a stinger, also called a burner or nerve pinch injury, is a neurological injury suffered by athletes, mostly in high-contact sports such as ice hockey, rugby, American football, and wrestling. The spine injury is characterized by a shooting or stinging pain that travels down one arm, followed by numbness and weakness in the parts of the arms, including the biceps, deltoid, and spinati muscles. Many athletes in contact sports have suffered stingers, but they are often unreported to medical professionals.

Nerve conduction study Diagnostic test for nerve function

A nerve conduction study (NCS) is a medical diagnostic test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. These tests may be performed by medical specialists such as clinical neurophysiologists, physical therapists, chiropractors, physiatrists, and neurologists who subspecialize in electrodiagnostic medicine. In the United States, neurologists and physiatrists receive training in electrodiagnostic medicine as part of residency training and in some cases acquire additional expertise during a fellowship in clinical neurophysiology, electrodiagnostic medicine, or neuromuscular medicine. Outside the US, clinical neurophysiologists learn needle EMG and NCS testing.

Brachial plexus injury Medical condition

A brachial plexus injury (BPI), also known as brachial plexus lesion, is an injury to the brachial plexus, the network of nerves that conducts signals from the spinal cord to the shoulder, arm and hand. These nerves originate in the fifth, sixth, seventh and eighth cervical (C5–C8), and first thoracic (T1) spinal nerves, and innervate the muscles and skin of the chest, shoulder, arm and hand.

Nerve injury Medical condition

Nerve injury is an injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injuries. 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. Usually, however, peripheral nerve injuries are classified in five stages, based on the extent of damage to both the nerve and the surrounding connective tissue, since supporting glial cells may be involved.

Group C nerve fiber One of three classes of nerve fiber in the central nervous system and peripheral nervous system

Group C nerve fibers are one of three classes of nerve fiber in the central nervous system (CNS) and peripheral nervous system (PNS). The C group fibers are unmyelinated and have a small diameter and low conduction velocity, whereas Groups A and B are myelinated. Group C fibers include postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots. These fibers carry sensory information.

Synkinesis is a neurological symptom in which a voluntary muscle movement causes the simultaneous involuntary contraction of other muscles. An example might be smiling inducing an involuntary contraction of the eye muscles, causing a person to squint when smiling. Facial and extraocular muscles are affected most often; in rare cases, a person's hands might perform mirror movements.

Denervation Loss of nerve supply

Denervation is any loss of nerve supply regardless of the cause. If the nerves lost to denervation are part of the neuronal communication to a specific function in the body then altered or a loss of physiological functioning can occur. Denervation can be caused by injury or be a symptom of a disorder like ALS and post-polio syndrome. Additionally, it can be a useful surgical technique to alleviate major negative symptoms, such as in renal denervation. Denervation can have many harmful side effects such as increased risk of infection and tissue dysfunction.

Nerve compression syndrome Human disease

Nerve compression syndrome, or compression neuropathy, is a medical condition caused by direct pressure on a nerve. It is known colloquially as a trapped nerve, though this may also refer to nerve root compression. Its symptoms include pain, tingling, numbness and muscle weakness. The symptoms affect just one particular part of the body, depending on which nerve is affected. Nerve conduction studies help to confirm the diagnosis. In some cases, surgery may help to relieve the pressure on the nerve but this does not always relieve all the symptoms. Nerve injury by a single episode of physical trauma is in one sense a compression neuropathy but is not usually included under this heading.

Peripheral nerve injury classification

Classification of peripheral nerve injury assists in prognosis and determination of treatment strategy. Classification of nerve injury was described by Seddon in 1943 and by Sunderland in 1951. The lowest degree of nerve injury in which the nerve remains intact but signaling ability is damaged is called neurapraxia. The second degree in which the axon is damaged but the surrounding connecting tissue remains intact is called axonotmesis. The last degree in which both the axon and connective tissue are damaged is called neurotmesis.

Axillary nerve palsy is a neurological condition in which the axillary nerve has been damaged by shoulder dislocation. It can cause weak deltoid and sensory loss below the shoulder. Since this is a problem with just one nerve, it is a type of Peripheral neuropathy called mononeuropathy. Of all brachial plexus injuries, axillary nerve palsy represents only .3% to 6% of them.

Epineurial repair

Epineurial repair is a common surgical procedure to repair a nerve laceration via the epineurium, the connective tissue surrounding nerve fibers originating from the spinal cord. It is intended to allow the restoration of sensory function. When a nerve is lacerated or cut, repair is done by sewing the cut ends together through the epineurium to increase the potential of the proximal part growing correctly along the route the degrading distal part leaves behind. Usual sensation and mobility will not be an immediate result because nerves grow at a rate of approximately 1 millimeter per day, so it will take a few months to notice the final outcome. Research in use of nerve grafts and nerve growth factors is being done to speed recovery time.

Nerve allotransplantation is the transplantation of a nerve to a receiver from a donor of the same species. For example, nerve tissue is transplanted from one person to another. Allotransplantation is a commonly used type of transplantation of which nerve repair is one specific aspect.

Cryoneurolysis, also referred to as cryoanalgesia, is a medical procedure that temporarily blocks nerve conduction along peripheral nerve pathways. The procedure, which inserts a small probe to freeze the target nerve, can facilitate complete regeneration of the structure and function of the affected nerve. Cryoneurolysis has been used to treat a variety of painful conditions.

Preferential motor reinnervation (PMR) refers to the tendency of a regenerating axon in the peripheral nervous system (PNS) to reinnervate a motor pathway as opposed to a somatosensory pathway. PMR affects how nerves regenerate and reinnervate within the PNS after surgical procedures or traumatic injuries. It is important to understand in order to further develop axonal regrowth surgical techniques. Further research of preferential motor reinnervation will lead to a better understanding of peripheral nervous system function in the human body regarding cell roles and abilities.

References

  1. 1 2 3 4 5 6 Sasser, Karen L. "Medical Student Curriculum in Neurosurgery." Medical Student Curriculum in Neurosurgery. Congress of Neurological Surgeons, n.d. Web. 11 Nov. 2013.
  2. 1 2 3 4 5 6 7 8 9 10 Campbell, W. W. (2008). "Evaluation and management of peripheral nerve injury". Clinical Neurophysiology. 119 (9): 1951–1965. doi:10.1016/j.clinph.2008.03.018. PMID   18482862. S2CID   41886248.
  3. 1 2 3 Burnett, M. G.; Zager, E. L. (2004). "Pathophysiology of peripheral nerve injury: A brief review". Neurosurgical Focus. 16 (5): E1. doi: 10.3171/foc.2004.16.5.2 . PMID   15174821.
  4. 1 2 Moran, S. L.; Steinmann, S. P.; Shin, A. Y. (2005). "Adult brachial plexus injuries: Mechanism, patterns of injury, and physical diagnosis". Hand Clinics. 21 (1): 13–24. doi:10.1016/j.hcl.2004.09.004. PMID   15668062.
  5. ↑ Greg. "Nerve Injury (Neuropraxia, Axonotmesis, Neurotmesis) and Healing." Current Health Articles. Health Hype, 4 Dec. 2004. Web. 11 Nov. 2013.
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