Peripheral Nerve Disorder

Etiology of peripheral nerve injury:

Acute traumatic injury or chronic repetitive trauma; compression and/or shear forces

Peripheral nerve injury classification:

• Neuropraxia

• Axonotmesis

• Neurotmesis

Nerve injury that causes a transient and focal loss of function (LOF) (sensory or motor):

Neuropraxia

• Often related to compressive forces causing ischemia (eg, carpal tunnel syndrome [CTS])

• Nerve dysfunction can be rapidly reversed or persist for weeks to months

• Positive prognosis if compression removed

  • Mildest form of nerve injury; no nerve degeneration

Neuropraxia

Focal damage to axon and myelin and varying degree of peripheral nerve connective tissue (endoneurium, perineurium, epineurium)

Axonotmesis

• Seen with increased-duration and larger-amplitude compressive (crush injury) or traction forces
  Prognosis is related to degree of connective tissue damage

• Axonal regrowth occurs at about 1 to 3 mm/day or 1 in/month

Axonotmesis

Severing of axon and myelin and all connective tissue structures

Neurotmesis

Complete loss of function; requires surgery

Neurotmesis

What is involved with neuroplasticity and peripheral nerve injuries?

Axonal regeneration and collateral sprouting

Axons that undergo regeneration do not remyelinate to preinjury level

• Can impact nerve conduction velocity, as well as speed and coordination of movement

Axonal regeneration

Intact axons can pick up denervated terminal targets (muscles)

• Often results in switching of muscle fiber type (from type 1 to type 2)

Collateral sprouting

Types of peripheral nerve injuries:

• Moneuropathy

• Moneuropathy multiplex

• Radiculopathy

• Plexopathy

Involvement of single nerve:

Mononeuropathy

Involvement of 2 or more nerves without clear pattern of polyneuropathy:

Mononeuropathy multiplex

Presentation of mononeuropathy multiplex is often related to other health conditions such as:

Diabetes mellitus, renal disease, chronic alcoholism

Involvement of nerve root(s):

Radiculopathy

Involvement of brachial or lumbosacral plexus:

Plexopathy

Risk factors of polyneuropathy:

• DM, renal failure, alcohol abuse

• Systemic autoimmune disease

• Autoimmune diseases

• Nutritional imbalances

• Hereditary

• Infections

• Cancers

• Medications

• Toxins

• Idiopathic onset

Disease process that primarily impacts myelin:

Segmental demyelination

If segmental demyelination is treated:

Remyelination can occur

Disease that impacts axons to a greater degree than myelin:

Axonal degeneration

How does axonal degeneration progress?

From distal to proximal

Examination of polyneuropathy:

• Sensory, motor, and autonomic symptoms (hair loss and vascular changes) occur in distal to proximal fashion (gloves and stocking)

  • Make sure to test both small (pain, temperature) and large (proprioception, kinesthesia) neural fiber involvement because impairment may vary

• Screen for autonomic dysfunction: vasodilation and loss of vasomotor tone (dryness,
  warmth, edema, orthostatic hypotension)

• Balance and fall risks

  • Balance difficulty with static posture; sensitive to eyes being closed and looking upward