Peripheral Nerve Conditions

Peripheral nerve disorders are rare in dogs. Most nerve problems are due to physical injury from traffic accidents, falls, and gunshot wounds.

Damage to a peripheral nerve causes both loss of sensation and loss of function in the muscles that are served by that nerve. If the nerve to the tail is damaged, for example, there will be temporary or permanent loss of the ability to sense pain in the rail area, to wag the tail, or to lift it when defecating. In the legs, one peripheral nerve supplies the muscles that flex, while the other supplies the muscles that extend. Car accidents can damage one or both of these nerves, producing either full paralysis of all the leg muscles or a partial parlysis affecting only a specific group of muscles.

Amputation of an affected limb may be necessary; however, a surgucal procedure to tramspose muscle attachments and produce a stiff but straight leg is sometimes an alternative.

Paralysis

Paralysis is the loss of contolled movement, which may be caused by the inability of the motor nerves to communicate with one or more muscles.. Complete paralysis, affecting all of the muscles, rarely occurs in dogs. Partial paralysis affecting the hind quarters is more common. Both types are mainly caused by spinal cord injury. Paralysis can be either temporaty or permanent.

Traumatic Paralysis

Spinal cord trauma from a traffic accident or other injury is the most common cause of paralysis. A slipped intervertebral disk pressing on the spinal cord can also cause partial or complete paralysis.

Diagnosis and Treatment of Traumatic Paralysis

Treatment is with intravenous methylprednisolone. Suregery can also be beneficial.

Tick Paralysis

Certain tick species found in North America carry a poison in their saliva that affects nerves. Initial signs include hind limb weakness about a week after a tick has attached itself. Full paralysis ensues in 1 to 3 days.

The degree of paralysis that a bitten dog suffers will vary with the environmental temperature and the amount of neurotoxin in the tick saliva. The toxin from the Australian Ixodes tick is more potent than that carried by North American ticks. Because the neurotoxin is temperature-sensitive, dogs recover faster when they are kept in air-conditioned premises.

Coon Hound Paralysis

The cause of this North American disease is unknown. It is seen most often in hunting dogs 1 to 3 weeks after contact with a racoon. Weakness begins in the hind limbs and progresses forward. Even the most severely affected dogs continue to be able to wag their tails. Spontaneous recovery usually occurs within weeks or months.

Myastenia Gravis

This condition occurs in three forms. In about 25% of affected dogs, full paralysis and breathing difficulties occur within 3 days. In another 40%, full paralysis develops more slowly; most of these dogs develop a flaccid esophagus and therefore cannot swallow. The ramaining 35% of dogs with myasthenia gravis do not develop full paralysis; the paralysis affects only specific areas, such as the face, pharynx, larynx, or esophagus.

Diagnosis and Treatment of Myastenia Gravis

The most common diagnostic test involves an injection of edrophonium chloride, a drug that prevents the breakdown of neurotransmitters at receptor sites; the drug temporariy increases muscle strength. A more accurate diagnostic serum antibody test is available, but this is less widely used. Affected dogs are injected with the drug neostigmine; the use of other drugs is controversial. Myasthenia gravis persists for months or years, but spontaneous remissions sometimes occurs.

Botulism

This condition is rare in dogs. It results from a neurotoxin that is produced by Clostridium botulinum bacteria, found in tainted canned food and carcasses. Paralysis, ascending from the hind limbs, occurs within hours or days of eating tainted food.

Diagnosis and Treatment of Botulism

Mildly affected dogs often recover without treatment. In other cases, antitoxin halts the progression of the paralysis, but it does not reverse any nerve damage that has occurred before treatment.

References:
1. Thelma Lee Gross. Skin Diseases of the Dog and Cat
2. Bernard F. Feldman, Joseph G. Zinkl, Nemi Chand Jain. Schalm's Veterinary Hematology