Classification Of Peripheral Nerve Injury

Guillain-Barré Syndrome

Guillain-Barré syndrome is one of the most common life-threatening diseases of the peripheral nervous system.
Guillain-Barré Syndrome is a rapidly progressive acute demyelinating disorder affecting motor axons that results in ascending weakness that may lead to death from failure of respiratory muscles over only several days.
Guillain-Barré Syndrome appears to be triggered by an infection or a vaccine that breaks down self-tolerance, thereby leading to an autoimmune response.
Associated infectious agents include Campylobacter jejuni, Epstein-Barr virus, cytomegalovirus, and human immunodeficiency virus.
The injury is most extensive in the nerve roots and proximal nerve segments and is associated with mononuclear cell infiltrates rich in macrophages.
Both humoral and cellular immune responses are believed to play a role in the disease process.

Chronic inflammatory demyelinating polyneuropathy
(CIDP) typically manifests as a symmetric demyelinating disease.
Both motor and sensory abnormalities are common, such as difficulty in walking, weakness, numbness, and pain or tingling sensations.
CIDP is immune-mediated and occurs at increased frequency in patients with other immune disorders, such as systemic lupus erythematosus and HIV infection.
CIDP follows a chronic, relapsing-remitting, or progressive course.
The peripheral nerves show segments of demyelination and remyelination.
In long-standing cases, chronically regenerating Schwann cells may concentrically wrap around axons in multiple layers in an onion-skin pattern.

Drugs and environmental toxins that interfere with axonal transport or cytoskeletal function often produce peripheral neuropathies.
The longest axons are most susceptible, so the resulting clinical presentation is often most pronounced in the distal extremities.
Peripheral nerves are often damaged in many different forms of systemic vasculitis including polyarteritis nodosa, Churg-Strauss syndrome, and Wegener granulomatosis.
Overall, peripheral nerve damage is seen in about a third of all patients with vasculitis at the time of presentation.
The most common clinical picture is that of mononeuritis multiplex with a painful asymmetric mixed sensory and motor peripheral neuropathy. Patchy involvement also is apparent at the microscopic level, as single nerves may show considerable interfascicular variation in the degree of axonal damage.

There is peripheral nerve involvement in both lepromatous and tuberculoid leprosy.
In lepromatous leprosy, Schwann cells are often invaded by Mycobacterium leprae, which proliferate and eventually infect other cells.
There is evidence of segmental demyelination and remyelination and loss of both myelinated and unmyelinated axons.
As the infection advances, endoneurial fibrosis and multilayered thickening of the perineurial sheaths occur.
Clinically, these patients develop a symmetric polyneuropathy that prominently involves pain fiers; the loss of sensation that results contributes to the tissue injury of the disease.
Tuberculoid leprosy shows evidence of active cell-mediated immune response to M. leprae, with nodular granulomatous inflammation situated in the dermis.
The inflammation injures cutaneous nerves in the vicinity; axons, Schwann cells, and myelin are lost, and there is fibrosis of the perineurium and endoneurium.
With this form of leprosy, patients have much more localized nerve involvement but do develop areas of abnormal sensation from the injury.

Peripheral nerve involvement results from the effects of the diphtheria exotoxin and begins with paresthesias and weakness; early loss of proprioception and vibratory sensation is common.
The earliest changes are seen in the sensory ganglia, where the incomplete blood-nerve barrier allows entry of the toxin.
There is selective demyelination of axons that extends into adjacent anterior and posterior roots as well as into the mixed sensorimotor nerve.

This virus is one of the few that produce lesions in the peripheral nervous system.
Latent infection of neurons in the sensory ganglia of the spinal cord and brain stem follows chickenpox, and reactivation leads to a painful, vesicular skin eruption in the distribution of sensory dermatomes (shingles), most frequently thoracic or trigeminal.
The virus may be transported along the sensory nerves to the skin, where it establishes an active infection of epidermal cells.
In a small proportion of patients, weakness is also apparent in the same distribution.
Although the factors giving rise to reactivation are not fully understood, decreased cell-mediated immunity is of major importance in many cases.
Affected ganglia show neuronal destruction and loss, usually accompanied by abundant mononuclear inflammatory infiltrates. Regional necrosis with hemorrhage may also be found.
The peripheral nerve shows axonal degeneration after the death of the sensory neurons.
Focal destruction of the large motor neurons of the anterior horns or cranial nerve motor nuclei may be seen at the corresponding levels. Intranuclear inclusions generally are not found in the peripheral nervous system.