Neurapraxia

Neurapraxia

Description, Causes and Risk Factors:

The mildest type of focal nerve lesion that produces clinical deficits; localized loss of conduction along a nerve without axon degeneration; caused by a focal lesion, usually demyelinating, and followed by a complete recovery. Term is often misspelled (neuropraxia), and often used, incorrectly, as a synonym for nerve lesion

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 (ischemia). 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.

Neurapraxia is a temporary interruption of conduction without loss of axonal continuity. In neurapraxia, there is a physiologic block of nerve conduction in the affected axons.

Causes:

  • Mechanical injury: Mechanical injury resulting from a tourniquet or other causes of external pressure can lead to nerve compression and therefore injury. The nerve may also be compressed by adjacent structures or from trauma in the body. A Compression nerve injury can result from crush injuries, pressure from fractures, hematoma, blunt injury and in compartment syndrome where swelling of tissues in a closed muscular compartment resulting in compression of the nerve or its blood supply.
  • Laceration injury: Laceration injury can result from blunt or penetrating injury. The nerve injuries cause irregular patterns of nerve damage. Nerve severance (cut) can occur but the severance is often not clean division as seen in cut injuries.
  • Penetrating injuries: Penetrating injuries can result in partial or complete severance of the nerves. It can result from wounds from stabbing or cut wounds from sharp objects.
  • Stretch injuries: Stretch injuries are common in fractures and dislocations. The injury results from the sudden stretch of the nerves during dislocation. Almost half of all shoulder dislocations lead to nerve injury but it is significantly less with other joint dislocations. A stretch injury to the peripheral nerves can also occur during certain surgical procedures.
  • Direct nerve injury: Direct nerve injury can result from high-velocity trauma sustained in motor accidents and in ballistic injuries. A displaced bone fracture can also cause direct nerve injury. Violent traction can result in injury to the nerve and even lead to severance.

Characteristics:

Neurapraxia is the mildest type of peripheral nerve injury.

  • There are sensory-motor problems distal to the site of injury.
  • The endoneurium, perineurium, and the epineurium are intact.
  • There is no Wallerian degeneration.
  • In neurapraxia, conduction is intact in the distal segment and proximal segment, but no conduction occurs across the area of injury.
  • Recovery of nerve conduction deficit is full, and requires days to weeks.
  • EMG shows lack of fibrillation potentials (FP) and positive sharp waves.

Symptoms:

Symptoms of neurapraxia include numbness and tingling, burning pain, muscle weakness, and cool skin. Depending on the location, symptoms of neurapraxia may include arm weakness, arm numbness, leg weakness or leg numbness

Diagnosis:

In order to fully determine the extent of the damage to the nerve, your doctor may order an EMG / NCV, an electrical conduction test to determine the passage of electrical currents through the nerves. These tests are sometimes done during actual surgery while the patient is sedated.

Your doctor may also order any of the following imaging techniques:

  • CT scan.
  • MRI.
  • MRI neurography.

Treatment:

There may be a recovery of nerve injury over weeks and months if there is no severance (cut). However, recovery of a severed nerve may never occur. The nerve repair process involves degeneration of the nerve followed by regeneration. The degeneration of nerve is called Wallerian degeneration. The process involves phagocytosis (Process in which phagocytes engulf and digest microorganisms and cellular debris; an important defense against infection) of the damaged segment of the nerve beyond the site of nerve injury. The regeneration of the nerve is guided by the presence of some important growth factors or neurotropic substances like the nerve growth factor (NGF). Many other growth factors and cytokines are also believed to affect the process of degeneration-regeneration.

Following degeneration of the nerve, the nerve begins regeneration. The regeneration starts at the proximal end of nerve at the site of injury. It progresses slowly to the distal part of the degenerated nerve. Regeneration occurs at a very slow rate. It occurs at a rate of 1 mm/day. The recovery takes longer time if the distance to be covered by regeneration is long. A nerve damaged closer to the muscle that it innervates recovers much earlier than a nerve which is damaged further away from the muscle.

The regenerated nerves may end up with abnormal connections. It can result in abnormal movements or sensations. An injured nerve that supplies muscles can resume its function only if the re-innervation happens within 18 months after the injury.

Nonsurgical treatment options include:

  • Acupuncture.
  • Massage therapy.
  • Medication.
  • Orthotics.
  • Physical therapy and rehabilitation.
  • Weight loss management.

Surgery can be done in case a 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.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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