Polyneuropathy in Dogs

Overview of Canine Polyneuropathy

Polyneuropathies are a group of diseases that affect multiple nerves in any combination. In dogs, they may be inherited or acquired later in life.

Causes of Canine 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.

Predisposing Factors

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.

Inherited polyneuropathies generally begin by the age of 6 months, while acquired neuropathies, depending on the specific disorder, may be seen in all ages.

What to Watch For

Signs associated with inherited polyneuropathies are generally slow and progressive. Signs in dogs may include:

• Generalized weakness
• Muscle tremors (shaking)
• Muscle atrophy (shrinkage)
• Ataxia (unsteady gait)
• Head tremors
• Seizures
• Blindness
• Depression

Signs associated with acquired polyneuropathies may progress rapidly or slowly, depending on the particular illness.

• A stiff-stilted gait often progressive to paralysis or paresis (incomplete paralysis)
• Weakness
• Muscle atrophy
• Anorexia
• Depression

Diagnosis of Polyneuropathy in Dogs

• Baseline tests to include a complete blood count (CBC), biochemical profile, and urinalysis are recommended in all patients and may be within normal limits. They may indicate underlying metabolic or neoplastic (cancer) disorder.
• Serum antinuclear antibody titer (ANA) may be positive, suggesting immune disease
• Titers or other blood tests screening for infectious organisms (N. caninum)
• Thyroid panel to assess thyroid function
• Radiographs (X-rays) of the chest may be normal, although they may support the findings of a dilated esophagus or underlying cancer.
• Electrophysiology, advanced, specialized testing, is the cornerstone for diagnosis. This includes electromyographic evaluation (EMG), motor and sensory nerve conduction and action potential amplitudes. These tests help differentiate myositis from polyneuropathy as the cause of weakness
• Muscle biopsy confirms evidence of denervation or loss of nerve function
• Nerve biopsy further delineates disease process

Treatment of Polyneuropathy in Dogs

• 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.
• Inherited polyneuropathies are generally untreatable.
• Immunosuppressive drugs are medications that suppresses the immune system, such as corticosteroids and azathioprine (Imuran). These are recommended in cases of immune mediated polyneuropathies.

Home Care

Administer all medication and diet as directed by your veterinarian. If any change is noted in your dog’s condition, notify your veterinarian. In particular, if coughing or difficulty breathing is observed, contact your veterinarian at once, as this may signal aspiration pneumonia secondary to a malfunctioning esophagus.

Depending on the underlying cause, life long therapy may be necessary in these patients. It is important to realize that, although in some cases where an underlying disorder has been identified and treated, the associated polyneuropathy will resolve; in others, despite treatment, it may not.

Avoid breeding dogs with inherited or Neospora-associated disease. Avoid contact with raccoons for dogs with a previous history of coonhound paralysis.