Disease of the Peripheral Nervous System 

     The PNS is affected by compressive lesions (tumors), vascular disruption,
     axonal degeneration, and segmental demyelination.

Peripheral Neuropathies

Tumors

Peripheral Neuropathies 

     Interference with action potential conductance along peripheral nerve(s).

     Wallerian degeneration

          Traumatic or ischemic induced transection of peripheral nerve leads to
          distal axonal degeneration and proximal sparing.  Nerve regeneration may
          lead to limited restoration of function.

     Primary axonal degeneration
          Group of disorders resulting from damage to neural cell body and
          subsequent axonal degeneration.  Nutritional and toxic causes are
          common.  Most common neuropathy in U.S. is induced by diabetes
          mellitus.
          Clinical: Patients often manifest a glove and stocking or dying back
                    neuropathy.  This can be either sensory or motor, often with
                    autonomic components.
 

    Segmental demyelination
          This group of disorders is characterized by loss of myelin with initial
          preservation of axons.  
          Guillain-Barre syndrome
               An acute peripheral demyelinative disorder often associated with a
               recent viral infection.  Rapid demyelination leads to ascending
               paralysis with severe respiratiory involvement.  May be autoimmune
               (cross-reactivity?)

PNS Neoplasms 

     The two most prevalent tumors of the PNS are schwannomas and
     neurofibromas.  They are both typically seen in adults except for patients with
     neurofibromatosis type I.  Usually solitary, the most common is the acoustic
     schwannoma that can lead to deafness in adults (>50).  Malignant
     transformation is primarily seen in neurofibromas in patients with von
     Recklinghausen's disease.