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                    Canine Polyneuropathy                   

talalogoa

Polyneuropathies are a group of inherited or acquired diseases that affect multiple nerves in any combination.  Polyneuropathy means "many abnormalities of the nervous system".  The condition is generally characterized by a lack of coordination and instability that leads to a laboured gait which has been described as a bunny hopping gait where the rear legs work together to prop up the dog rather than to propel him. The degree of severity varies from dog to dog, some only exhibiting mild forms whilst others severe forms. The dog may fall down, walk on the tops of his feet (with the foot folded under itself) or his gait may just look a little off. Exercise intolerance, loss of muscle mass, changes in voice due to an affected larynx and problems swallowing and regurgitating have also been described. First indications of the problem may be subtle — a dog that no longer jumps up on his dog house, a dog that lies down to eat, a dog that no longer jumps up and down at feeding time or shows a slight tremor in his legs. It cannot be emphasized enough that symptoms may vary considerably from dog to dog.

Causes of Polyneuropathy
Inherited Causes Spinal muscular atrophy, which is shrinkage of the muscles of the spine      

Demyelination, which is destruction of the covering of the nerves

Lysosomal storage diseases are inherited deficiencies of particular enzymes creating an inability to perform normal metabolic functions
Acquired Causes Immune-mediated or associated with a hyperactive immune system

Systemic lupus erythematosus, which is a multi-organ immune disease

Polymyositis, or inflammation of the muscles

Polyarthritis, or inflammation of the joints

Glomerulonephritis, or inflammation of a part of the kidneys
Infectious Causes Neospora canis, a protozoa
Metabolic Causes
 Diabetes mellitus

Hypothyroidism

Paraneoplastic Syndrome

Paraneoplastic syndrome is a collective term for disorders arising from metabolic effects of cancer on tissues remote from the tumor. Some of these include: Insulinoma, Carcinoma, Mast cell tumors, Lymphosarcoma, Osteosarcoma, Multiple myeloma
Toxic or Drug Causes
 Heavy metals (thallium, mercury lead, copper, zinc)

Chemicals (organophosphates, carbon tetrachloride, lindane)

Chemotherapy (vincristine, vinblastine, cisplatin)
Other
 Coonhound paralysis which is acute/sudden inflammation of multiple nerve roots caused by contact with an infected raccoon.


Various breeds of dogs may be affected. Specific breeds are associated with specific inherited neuropathies. Coonhounds have a higher incidence than other breeds for acquired neuropathies, specifically, coonhound paralysis.

Different Types of Neuropathies
Botulism  Botulism is very rare in dogs and usually follows feeding on carrion. Symptoms include weakness, difficulty eating, acute facial nerve paralysis, and megaesophagus. Compared to other species, dogs and cats are relatively resistant to botulism.
Dancing Dobermann disease
This primarily affects the gastrocnemius muscle in Dobermanns. It usually starts between the ages of 6 to 7 months. One rear leg will flex while standing. Over the next few months it will begin to affect the other rear leg. Eventually, the dog is alternatively flexing and extending each rear leg in a dancing motion. Dancing Dobermann disease progresses over a few years to rear leg weakness and muscle atrophy. There is no treatment, but most dogs retain the ability to walk and it is painless.
Distal symmetric polyneuropathy
Symptoms include atrophy of the distal leg muscles and the muscles of the head, and rear limb weakness. There is no treatment and the prognosis is poor. This is most commonly seen in Chesapeake Bay Retrievers, St. Bernards, Great Danes, Newfoundlands, Collies and Labrador Retrievers.
Giant axonal neuropathy
This is a rare disease in the German Shepherd Dog. It usually becomes evident between the ages of 14 and 16 months. Symptoms include rear limb weakness, decreased reflexes, muscle atrophy, megaesophagus, and loss of bark. There is no treatment and a poor prognosis.
Hypertrophic neuropathy
This is also known as canine inherited demyelinative neuropathy (CIDN) and is inherited in the Tibetan Mastiff. Symptoms usually start between the ages of 7 to 10 weeks, and include weakness, decreased reflexes, and loss of bark. Sensory fumction remains, but there may be a poor gait or an inability to walk. There is no treatment and a guarded prognosis. It is inherited as an autosomal recessive trait.
Hypoglycemia

Polyneuropathy is especially seen in conjunction with insulinoma.
Myasthenia gravis
Rottweiler distal sensorimotor polyneuropathy
This is characterized by distal muscle denervation, but the cause is unknown. It affects young adult Rottweilers. The symptoms include weakness of all four legs and decreased reflexes. The disease is gradually progressive. Treatment is possible with corticosteroids, but the prognosis is poor.
Sensory Neuropathies
These are inherited conditions in dogs and cause an inability to feel pain and a loss of proprioception. Self mutilation is often seen. There is no treatment, and the prognosis is poor in severe cases. There are several affected breeds.
Boxer

usually occurs at around two months of age as a slowly progressive disease.
Dachshund (longhaired)
usually occurs between 8 and 12 weeks of age, and causes urinary incontinence, loss of pain sensation all over the body, and penis mutilation. It is probably inherited as an autosomal recessive trait.
English Pointer
usually occurs between the ages of 3 and 8 months and most commonly involves licking and biting at the paws. There is no treatment and a poor prognosis. It is inherited as an autosomal recessive trait.
Spinal muscular atrophy
This occurs in dogs and is caused by the death of nerve cells in the spinal cord. This progressive disease has no treatment and a poor prognosis. Affected breeds include the Swedish Lapland Dog, Brittany Spaniel, English Pointer, German Shepherd Dog, Rottweiler, and Cairn Terrier.
Tick paralysis
This is an acute, ascending motor paralysis that occurs in dogs; cats seem to be resistant. The cause is a neurotoxin in the saliva of certain species of adult ticks. Dermacentor species predominate as a cause in North America, while Ixodes mainly causes the disease in Australia. The onset of symptoms is 5 to 9 days after tick attachment, and include incoordination progressing to paralysis, changed voice, and difficulty eating. Death can occur secondary to paralysis of the respiratory muscles, but in North America there is a good prognosis once the ticks are removed. Recovery is usually in 1 to 3 days. In Australia, however, it is a more severe disease with cranial nerve effects, and death can occur in 1 to 2 days.


Inherited polyneuropathies generally begin by the age of 6 monthsand are generally slow and progressive, while acquired neuropathies, depending on the specific disorder, may be seen in all ages.  Symptons can range from Generalized weakness, Muscle tremors (shaking), Muscle atrophy (shrinkage), Ataxia (unsteady gait), Head tremors, Seizures, Blindness, Depression.  Unfortunately there is no treatment for Inherited polyneuropathies.

Signs associated with acquired polyneuropathies may progress rapidly or slowly, depending on the particular illness.  Symptons can range from a stiff-stilted gait often progressive to paralysis or paresis (incomplete paralysis), Weakness, Muscle atrophy, Anorexia, Depression,

Because the disease is seemingly rare it may often be misdiagnosed or undiagnosed. There are also cases of some spinal problems (lesions or bone spurs) producing superficially similar symptoms but it would be extremely unlikely for bone spurs to cause absolutely symmetrical symptoms like this does. Because of this it is important to get a positive diagnosis from a school of veterinary medicine or a veterinary neurologist where they can run tests that your local vet cannot do. The diagnostic tests include nerve and muscle biopsies, electromyography and nerve conduction velocities. If the results are positive, these tests will show a deterioration of the myelin sheath of the nerve and conductivity may be slower than is normal. They may also do x-rays to see if there is an enlarged esophagus.

Most patients are treated on an outpatient basis. Supportive care may be required to prevent wounds and decubital ulcers (bed sores) in severely affected patients who cannot walk.  Fluid and electrolyte therapy, as well as nutritional support, may be necessary in some patients, as some have a malfunctioning esophagus and cannot support themselves.  In cases where an underlying disorder has been identified, specific therapy for that disorder should be instituted. Remove/discontinue any drugs/toxins that may be causative.  Immunosuppressive drugs are medications that suppresses the immune system, such as corticosteroids and azathioprine (Imuran). These are recommended in cases of immune mediated polyneuropathies.

Affected dogs should not be bred


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