Nervous system disorders alter the dog’s capacity to sense the environment around it and respond to it effectively. They can result from diseases and other abnormalities that affect the central or peripheral nervous systems. Changes in the behavior of the dog, such as lack of balance or coordination may be the initial symptoms of the disorders affecting the nervous system. Tremors and seizures are typical signs of nervous system involvement. The dog may have numbness and weakness in the affected limb, sometimes accompanied by pain, and often culminating in paralysis. The location of the injury, and its severity, may influence the extent of sensory and motor impairment.
Effects of the injuries affecting the nervous system In Dogs
If the injury is to the spinal cord, its main effects are numbness and paralysis of the areas that come after the point of injury. If the injury is mild, the dog may develop slight weakness in the limbs which may be apparent by clumsy movements. Weakness may be greater, and may cause limping, in case of moderate injury. Complete absence of feeling and paralysis of the affected limbs may occur if the spinal cord injury is severe. Some spinal cord injuries do not cause paralysis of the limbs. The area affected depends on the nerves that are involved. A spinal cord injury in the lower back area may cause the dog to lose its control over the bladder.
The symptoms of injuries to the brain may differ according to the part of the brain that is involved. If the brain stem is injured, it may result in weakness in one or more limbs besides loss of balance. The reflexes may become overactive or the dog may fall into a stupor, which may lead to coma. Loss of balance accompanied by tremors and uncoordinated limb and head movements often indicate a cerebellum injury. If the cerebrum is injured the dog may lose one or more of its sensory functions such as hearing and smell. If the sense of vision is affected, it may become either partially or completely blind. Behavioral changes such as circling or repeated pacing, seizures, stupor that may lead to coma are also seen. The dog may become unable to recognize its own owner.
The effect of the damage caused by nervous system injuries may not be apparent immediately. Many symptoms start appearing after a day or two. Internal bleeding in the brain or swelling of the tissues may be responsible for the late onset of some symptoms. Dogs rarely have strokes resulting from high blood pressure or arterial blocks.
Disease conditions affecting the nervous system Of Dogs
Congenital abnormalities, metabolic and nutritional disorders, degenerative and inflammatory conditions, poisoning by toxic substances, infections and cancerous growths can impair the nervous system.
Congenital abnormalities or birth defects usually become apparent soon after the birth. Many of them may be inherited conditions. While some of them may cause a progressive but irreversible degeneration of the neurons in the puppy before it is a year old, others, like epilepsy, may appear only after 2-3 years.
Certain viruses or other microorganisms may cause infections that affect the nervous system. Some inflammatory conditions are auto immune diseases. Inflammation of the outer tissue layers of the brain and the spinal cord resulting in meningitis may be caused by the self-destructive action of the immune system. Chemical poisoning of the nerve tissue may be caused by the ingestion of rat poison, pesticides, antifreeze or other such toxic chemicals. Certain sedatives and chocolate may be toxic to dogs. Botulism toxin from food poisoning and tetanus toxin from injuries, venom of coral snakes and tiger snakes, as well as tick bites may cause nervous system disorders that may lead to paralysis.
Metabolic disorders such as kidney and liver failure may affect the nervous system. Shortness of breath and low blood sugar may starve the brain of oxygen and glucose, resulting in cell death. Thyroid disorders may have adverse neurologic effects. Deficiency of vitamins, especially of thiamine results in neurologic symptoms such as stupor and lack of motor control. It may even cause seizures as well as coma.
Tumors of the Nervous System In Dogs
Tumors affecting the nervous system may be more prevalent in older dogs, but occasionally they appear in younger dogs too. Their effect of the tumors on the neurologic functions depends on their location, behavior and growth patterns. In dogs, the primary tumors usually appear in the brain tissue compared to the spinal cord and the nerves of the peripheral nervous system. Brain tumors have the highest incidence in brachycephalic breeds, characterized by their short snouts and flattened faces, such as Boston Terriers, English Bulldogs, and Boxers. The adult dogs are more commonly affected.
Various tests are available to detect and confirm brain tumors in dogs. X-rays, CT scans, MRI scans and myelography may help in the diagnosis. Testing of the cerebrospinal fluid obtained through needle aspiration may also help in diagnosing brain cancers.