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George E. Carvell, PhD, PT   University of Pittsburgh
 
PERIPHERAL NERVE DYSFUNCTION V: DEMYELINATING NEUROPATHY
Ben.  fig 13-31  p 421
Peripheral Neuropathies are diseases of the peripheral nervous system axons anywhere from the roots to distal axonal branches in the periphery. Segmental Demyelinating Diseases result in loss of myelin and possibly destruction of the Schwann Cells responsible for myelinating these axons. Both sensory and motor axons may be affected but some neuropathies have a predilection for one type vs. another. Loss of myelin results in focal slowing of nerve conduction, or, if severe, a focal conduction block may be present. Nerve Conduction Studies may reveal such deficits if the test includes the involved segment of nerve. This process may be multisegmental and severe such as Acute Guillian Barre
Syndrome, or the lesion may be localized to a single site of nerve compression or ischemia, e.g., Mild, Acute Carpal Tunnel Syndrome. Some demyelinating diseases progress to axonal degeneration with resultant denervation of involved motor units. Sensory changes associated with large fiber conduction (e.g., discriminative touch, proprioception) may be found, as well as, reduced or absent deep tendon reflexes for involved musculature. Frank electrical signs of muscle denervation may be absent in the clinical EMG needle exam unless a secondary axonal degeneration is present. Weakness may be a labile finding depending on the stage and severity of nerve involvement. Early muscle fatigue may be the most significant functional problem that may or may not be revealed by a routine manual muscle exam. Polyneuropathies are often distal and symmetric. Examples include diabetic, alcoholic, or toxic polyneuropathies that show distal muscle weakness and atrophy, and a distal "stocking-glove" pattern of sensory loss. On the other hand, a spinal nerve root entrapment due to a herniated disc will show a radiating/radicular pattern associated with the appropriate dermatomal and myotomal reference. There are many variations to these patterns of involvement, e.g., small fiber vs. large fiber disease. Some investigators have suggested that the nerves are sick and therefore more susceptible to a second insult such as pressure or ischemia.
GMOMM  2001
Recruit motor units more often/
Unit of force