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Nerve Disorder Affecting Multiple Nerves in Dogs

Peripheral Neuropathy (Polyneuropathies) in Dogs

Polyneuropathy in dogs is a condition that impacts multiple peripheral nerves, distinguishing itself from the central nervous system, which benefits from the protection of the spinal vertebrae and skull bones. Peripheral nerves, however, are more vulnerable to physical injury and toxic substances due to their exposure to the external environment. These nerves extend throughout the body and play crucial roles in conscious movement (somatic), automatic physical responses (autonomic), and the functioning of the digestive system (enteric).

Myelin, a fatty lipid material serving as insulation for certain nerve fibers, can undergo demyelination, a process where it deteriorates, leading to the loss of electrical signals within the nerves and consequent impairment of function. Alternatively, axonal degeneration can occur alongside secondary demyelination. Axonal degeneration refers to the deterioration of the nerve fibers within the myelin sheath.

Symptoms and Types

Disorders affecting motor and sensorimotor nerves (responsible for automatic movement):

  • Weakness or paralysis observed in all four legs
  • Decreased reflexes or absence of reflexes (automatic physical responses)
  • Reduced muscle tone or lack thereof
  • Muscle atrophy (muscle deterioration)
  • Muscle tremors or trembling

Disorders affecting sensory nerves (related to pain/pleasure nerve receptors):

  • Spatial disorientation (inability to perceive one’s surroundings accurately)
  • Weakness progressing to loss of consciousness
  • Absence of muscle deterioration
  • Absence of muscle tremors
  • Hypothyroidism (underactive thyroid gland)
  • Paralysis of the voice box
  • Paralysis of the throat/esophagus, leading to difficulty in eating and drinking
  • Facial paralysis
  • Dizziness and instability

Dysfunction of the autonomic nervous system (not under conscious control):

  • Dry nose
  • Dry mouth
  • Reduced tear production leading to dry eyes
  • Slow heart rate
  • Absence of anal reflex

Causes

Congenital or inherited factors

  • Dysautonomia: characterized by abnormal functioning of the autonomic nervous system, resulting in excessive body fluid output, lack of reflexes, and coordination issues.

Immune-related diseases

Metabolic disorders

  • Hypothyroidism (underactive thyroid gland)
  • Pancreatic tumor, affecting insulin production

Infectious causes

  • Neospora caninum parasite: impacts the hind legs, potentially causing paralysis, muscle atrophy, and immune system impairment. Transmission occurs through ingestion of infected animal meat, contact with infected animal feces (often from another dog), or soil containing residual infected feces. Transmission from pregnant animals to their fetuses via the placenta is also possible.
  • Coonhound paralysis (polyradiculoneuritis): primarily affects hunting dogs exposed to raccoons carrying the infection. It affects all four legs and the muscles controlling barking and breathing.

Side effects of cancer medications

  • Toxic substances
  • Thallium: found in rodent poison
  • Organophosphates: present in fertilizers and pesticides
  • Carbon Tetrachloride: used in insecticides
  • Lindane: employed for weed, insect, and lice eradication

Diagnosis

Your veterinarian will conduct a comprehensive physical examination of your dog, considering the history of symptoms and any potential triggering incidents. To confirm or rule out underlying diseases, a chemical blood profile, complete blood count, electrolyte panel, and urinalysis will be performed. Additional blood tests and a spinal tap may also be recommended by your veterinarian to investigate specific disorders.

Chest and abdominal x-rays are essential for identifying visible peripheral polyneuropathies. X-ray and ultrasound imaging can help rule out or confirm the presence of cancer. However, the primary diagnostic tool for detecting peripheral neuropathies is electrophysiology, which measures the electrical flow within the body’s tissues and cells. Additionally, analyzing tissue samples (biopsy) from muscles or peripheral nerves can provide further insights into the disease process affecting your dog.

Treatment

Most animals can undergo treatment on an outpatient basis. However, dogs with acute polyradiculoneuropathies, characterized by inflammation at the roots of spinal cord nerves, are susceptible to respiratory failure and should be hospitalized for observation during the early stages of the disease to mitigate this risk. Dogs diagnosed with dysautonomia require hospitalization to receive fluid therapy and/or parenteral feeding.

On the other hand, dogs with hyperchylomicronemia may experience spontaneous recovery after two to three months of being fed a low-fat diet. For dogs diagnosed with diabetes mellitus, close monitoring of blood glucose levels and diet is essential.

Physiotherapy is an excellent adjunct treatment for patients with peripheral polyneuropathies as it promotes the restoration of affected musculature and nerve memory.

Living and Management

It’s crucial to recognize that the cause of many polyneuropathies may remain unknown, and addressing the primary cause might not result in a cure for your dog. In some instances, peripheral nerves may continue to deteriorate, leading to the progression of your dog’s condition.

For dogs diagnosed with congenital or inherited forms of polyneuropathies, breeding should be avoided. It’s generally recommended to neuter dogs suffering from this condition to prevent unintended breeding. For instance, female dogs infected with the Neospora parasite should not be bred, as the parasite can transmit to the fetus through the placenta.

Dogs affected by coonhound paralysis (polyradiculoneuritis) should be safeguarded from further exposure to raccoons since prior infection does not confer immunity against future occurrences.

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