The Mechanics of the PNS Neuropathies


INTRODUCTION

It is intended that the subject of this discussion apply to the entire group of the Neuropathies of the Peripheral Nervous System. In the interest of brevity, Reflex Sympathetic Dystrophy (RSD) will be used as the model of a "typical neuropathy". A typical neuropathy[1] presents the following initial symptoms:

  • Severe burning pain.
  • Hyperesthesia - abnormal skin sensitivity to touch
  • Paresthesia - burning, pricking, tingling, or itching
  • Edema - fluid accumulation
  • Muscular spasms
  • Joint stiffness and limited mobility
  • Vasospasms - sudden constriction of blood vessels, reducing blood flow
  • Roseola - a red discoloration of the skin resulting from sudden oxygenation - the skin is warm and dry
  • Cyanosis - blue-gray discoloration of the skin resulting from hypoxia (oxygen starvation) - skin is cold and damp
  • Hyperhidrosis - profuse sweating
As the disease progresses, the following changes occur:
  • Pain worsens and becomes more generalized
  • Edema spreads and worsens
  • Hair (in the affected areas) falls out
  • Nails become brittle, burst and have and become ridged
  • Osteoporosis occurs and becomes more pronounced
  • Joints swell
  • Muscles atrophy
  • Flexor tendons retract and subluxation (incomplete or partial dislocation of a bone in a joint) occurs
  • Disease may spread throughout the entire body

THE POSSIBLE ETIOLOGIES (CAUSES)

The Sympathetic Nervous System (SN) and the Parasympathetic Nervous System (PN) function as a closed loop servo-control system. The SN uses vasoconstriction to increase the blood flow by constricting the blood vessels, raise the pulse rate and blood pressure. The SN uses vasodilation to decrease the blood flow by dilating the blood vessels, lower the pulse rate and blood pressure. Thus, we have a closed loop-servo control system such that the SN and the PN are constantly (in real-time) trying to adjust the tissues and organs and maintain the blood supply to meet the needs of the body as perceived by the Sensory-Motor Nervous System. Together the SN and the PN regulate the blood flow, pulse rate, blood pressure, and body temperature as set points on an automatic control system - much like thermostat.

When these control functions fail, problems arise. Almost all of the PNS Neuropathies result from too much vasoconstriction or too much vasodilation. There is recent evidence that an overabundance of either vasoconstriction or vasodilation may be due to causes other than / or in addition to the SN or the PN. The hormone vasopressin when produced will cause vasoconstriction.

Other possible causes of the Neuropathies are:

  • The erroneous up-regulation or down-regulation of nociceptors (the pain receptors) thus telling the brain falsely, that more pain exists than is present.
  • Defects in the various neurotransmitters that are used to signal pain and other information for the brain.
    The copyright of the article The Mechanics of the PNS Neuropathies in Neurological Diseases is owned by Les Abrams. Permission to republish The Mechanics of the PNS Neuropathies in print or online must be granted by the author in writing.

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