Overview of Acute Canine Polyradiculoneuritis (Coonhound Paralysis)
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
Symptoms of acute polyradiculoneuritis may include:
- 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 of Polyradiculoneuritis in Dogs
- 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 of Polyradiculoneuritis in Dogs
- 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-depth Information on Acute Polyradiculoneuritis (Coonhound Paralysis)
In normal dogs, 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.