The central nervous system (CNS) comprises the brain and spinal cord; the peripheral nervous system (PNS) consists of the neural pathways running between the CNS and the organs and limbs of the body. The PNS contains both motor (movement) and sensory neurons or nerve fibers; neuropathy is the disruption of nerve impulses within the PNS.
Polyneuropathy is a serious, unpredictable, occasionally progressive, and life threatening neurological disorder that occurs when many nerves throughout the body of a dog malfunction simultaneously. It may be acute and appear without warning, or chronic and develop gradually over a longer period of time. Many polyneuropathies have both motor and sensory involvement; some also involve dysfunction of the autonomic nervous system.
Unlike the central nervous system, which has the vertebrae of the spine, and the bone of the skull to protect it, the peripheral nerves are more exposed to the elements that enter into the body and come into contact with the body, so they are more susceptible to physical injury and toxic damage. They are spread over the entire body, and are responsible for conscious, coordinated movement (somatic), for automatic physical responses (autonomic), and for the movement of the digestive system (enteric).
Myelin, the white, fatty, lipid material that acts as an insulator coat (also called a sheath) for some nerve fibers, can be lost through a process called demyelination, a condition that causes the myelin to deteriorate, resulting in electrical signals in the nerves being lost, and impairing function. Or, there may be axonal degeneration with secondary demyelination. Axonal degeneration occurs when the actual nerve fibers deteriorate within the myelin sheath.
Common signs and symptoms of this condition are
Motor and sensorimotor nerve disorders (automatic movement):
Weakness or paralysis in all four legs
Weak reflexes, or lack of reflexes (automatic physical responses)
Weak to no muscle tone
Muscle deterioration (atrophy)
Muscle tremors, trembling
Sensory nerve disorders (pain/pleasure nerve receptors):
Spatial disorientation (inability to judge the space around oneself)
Weakness to loss of consciousness
No muscle deterioration
No muscle tremors
Under-active thyroid gland
Paralysis of the voice box
Paralysis of the throat/esophagus, affects ability to eat and drink
Dysfunctioning autonomic nervous system (not under conscious control) :
Dry eyes – low tear production
Slow heart beat rate
Lack of an anal reflex