Acute Polyradiculoneuritis (Coonhound Paralysis)

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Acute polyradiculoneuritis is a widespread disorder of the peripheral nervous system with a sudden onset. The brain and spinal cord comprise the central nervous system, whereas the nerves leaving the spinal cord comprise the peripheral nervous system. It is a disease that causes damage to the nerves themselves, as well as to the myelin, which is a specialized substance that surrounds many nerves and allows for rapid transmission of nervous impulses.
The cause of polyradiculoneuritis is unknown, but it is believed to be an immune mediated or autoimmune process, which is associated with inflammatory cells (white blood cells) attacking the nerves. The immune system normally protects against infection by attacking organisms that are foreign to the body. In immune mediated diseases, the immune system targets and destroys its own cells, in this case the nerves.

This is the most common inflammatory peripheral nervous disorder in dogs. It is most commonly seen in hunting dogs following exposure to raccoons, hence the alternative name of coonhound paralysis. There are no specific breed or sex predispositions. It can also be seen in dogs without previous exposure to raccoons. Adult animals are generally affected. A similar disease process has been described in the cat, but this is very rare.

What to Watch For

  • Weakness starting in the hind legs and progressing to all legs
  • Weak bark
  • Development of severe weakness
  • Total inability to stand
  • Shallow breaths or difficulty breathing

    Diagnosis

  • Complete history and physical exam

  • Neurologic exam

  • Complete blood count (CBC)

  • Biochemical profile

  • Urine analysis

  • Electrodiagnostic testing. This evaluates the electrical activity in the nerves and muscles and assesses their function.

  • Cerebrospinal fluid (CSF) tap. The CSF is the fluid that bathes the brain and spinal cord. This can be collected for analysis.

  • Arterial blood gas (ABG). This evaluates respiratory function.

    Treatment

  • Supportive care, including appropriate bedding
  • Physical therapy of the limbs
  • Respirator if respiratory paralysis occurs

    Home Care and Prevention

    Continued supportive care. Recovery may take weeks to months. The affected dog may require assistance with eating and drinking. Physical therapy is necessary several times a day and the dog should be kept clean.

    Avoid exposure to raccoons. Dogs that have had one bout of polyradiculoneuritis may develop it again, so it is imperative to avoid re-exposure in these cases.

  • In normal animals, electrical signals travel from the brain down the spinal cord and then follow the path of individual peripheral nerves. The nerves branch and supply the muscles of the body. When the electrical signal reaches the muscle, it results in muscle contraction and movement. Therefore, widespread diseases of the peripheral nervous system cause muscular weakness and in severe cases, paralysis.

    Dogs with polyradiculoneuritis often begin showing signs of weakness one to two weeks following raccoon exposure, although the disease has been reported in animals with no history of exposure. Something in the raccoon's saliva is thought to initiate the damaging immune response. Weakness most often starts in the hind legs and the dog's bark may also be noticeably weaker than normal. Signs generally worsen over a period of about 10 days, although however complete paralysis can occur within 24 hours in rapid cases. In these cases, there is also a larger risk that respiratory muscles will become paralyzed and the dog will not be able to breathe.

    Other diseases that cause similar clinical signs include:

  • Botulism. Botulism is caused by the toxin produced by a type of bacteria called Clostridia. Dogs are most likely to be exposed to the toxin following ingestion of dead animals. The bacteria also proliferate in spoiled foods. The overall symptoms of botulism are quite similar to polyradiculoneuritis but there are subtle neurologic differences that can be picked up by the veterinarian. Special tests can be run to identify the toxin in animals with suspected toxicity.

  • Tick paralysis. This is another disorder caused by a toxin. The toxin comes from certain species of ticks and produces paralysis. Typically, physical exam reveals an engorged tick and removal of the tick causes resolution of the paralysis.

  • Protozoal polyradiculoneuritis. Infections with protozoal organisms (Toxoplasma and Neospora) can cause neurologic dysfunction as well. This type of polyradiculoneuritis is most often seen in young dogs, and may involve other clinical signs in addition to the neurologic disease.

  • Myasthenia gravis. Myasthenia is another immune mediated disease that prevents normal transmission between nerves and their respective muscles. It most often causes episodes of weakness with periods of recovery in between. It rarely causes weakness as profound as what is seen with polyradiculoneuritis.

  • Diagnosis

  • Complete history and physical exam. A thorough history is important to ascertain the possibility of exposure to raccoons, ticks and toxins. A thorough physical exam will assist in choosing the appropriate diagnostics.

  • Neurologic exam. Careful assessment of the nervous system is imperative to determine the nature of the nervous system disorder. Animals with a peripheral nerve disease have weak muscles with diminished tone and decreased to absent reflexes. Those that are still able to walk may appear lame and have a stilted gait, although they are aware of where they are placing their feet. Animals with central nervous system disease may have behavior changes, walk with a drunken appearance and have stiff limbs. A neurologic evaluation not only pinpoints the part of the nervous system involved, but also assesses how widespread the problem is.

  • Complete blood count. A CBC evaluates the red and white blood cells as well as the platelets. These would all likely be normal with polyradiculoneuritis, but the test may help rule out other disease processes.

  • A biochemical profile. This test evaluates blood sugar, blood proteins and electrolytes, and provides information about liver and kidney function. This is useful to get an overall idea about metabolic function. Animals with profound electrolyte disturbances (potassium and calcium in particular) or low blood sugar may also show signs of severe weakness.

  • Urinalysis. Evaluation of the urine is part of a complete laboratory assessment and gives a better indication of kidney function than the biochemical profile alone.

  • Electrodiagnostic testing. Tests in this category include electromyography (EMG) and nerve conduction studies. These are specialized tests that examine the electrical activity in nerves and muscles and allow an accurate assessment of nerve and muscle function. They may be helpful in supporting the diagnosis of polyradiculoneuritis. However, abnormalities in these tests don't occur until about 6 to 7 days after the animal begins showing signs of weakness. These tests must be performed by a neurologist with specialty training.

  • Cerebrospinal fluid tap. A CSF tap involves collecting the CSF fluid by inserting a small needle into the space around the spinal cord. This requires that the patient be under anesthesia. Analysis of this fluid in dogs with polyradiculoneuritis often reveals elevated levels of protein. Evaluation of the fluid may help rule out other causes of the clinical signs.

  • Arterial blood gas. An ABG provides information about how well the animal is breathing and if there are appropriate oxygen levels in the blood. In patients that appear to be demonstrating weakness of the respiratory muscles, this test is a useful way to assess the need for a respirator to assist breathing.

    Therapy In-depth

    There is no specific treatment for polyradiculoneuritis. Most animals recover over a period of 3 to 6 weeks, but some animals may take many months to recover, or may never recover completely. The most important aspect of treating these patients is to provide ample supportive care. Treatment consists of:

  • Soft bedding or a waterbed is necessary to prevent bed sores since animals are generally paralyzed when the disease is at its worst point. Additionally, it is important to turn the animals onto their opposite side several times a day. This insures that the lungs are not being constantly compressed on one side, which may make them more prone to infection.

  • Physical therapy is an important component of care. Paralyzed muscles atrophy or shrink and then develop contracture (muscle shortening) secondary to lack of use. Massaging the muscles and moving the limbs manually, including flexing and extending the joints several times a day help limit the secondary muscle damage. Hydrotherapy with whirlpool baths is also appropriate, if available.

  • Ventilation. Mechanical ventilation, or assisted breathing on a respirator, may be required in cases that develop respiratory muscle paralysis. In these cases, the animals die without a respirator. This can only be performed at specialty practices or university veterinary hospitals and is an extremely labor intensive and expensive procedure.

  • Animals generally maintain their ability to urinate and defecate, but they can develop urine scalding and secondary skin infections if they are not kept very clean, as they cannot get up to eliminate. Very careful hygiene is important.

  • Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not improve over the expected time frame.

    This disease generally follows a long course. Once the pet is stable, much of the supportive care will be done at home. This can be a real challenge, especially in large dogs. If supported in an upright position, most dogs can drink and eat on their own. To avoid the risk of inhaling their meals, it's imperative to keep your pet upright while eating and drinking. Additionally, offering water frequently is important to prevent dehydration.

    Infections associated with the respiratory tract, skin and urinary tract are possible concerns in bedridden patients. Signs to watch for that may be an indicator of infection include cough, nasal discharge, labored breathing, rashes or irritated skin, blood in the urine or apparent straining to urinate. Any of these symptoms should prompt a call to your veterinarian.

    Follow-up care with your veterinarian allows assessment of improving neurologic function. Additionally, infection may be discovered earlier if your pet is evaluated by your veterinarian at regular intervals during the illness.

    Relapses or recurrence of disease are not uncommon, so dogs that develop disease following raccoon exposure should be retired from hunting.

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