A stroke is the sudden and severe rupture or blockage of a blood vessel that deprives part of the brain of its normal blood supply, causing loss of consciousness, paralysis and other clinical signs. The brain requires a significant supply of oxygen and glucose to function properly, but it has minimal space for storage of these substances. As a result, it is extremely important for the brain to have a constant blood supply, because oxygen and glucose are transported in blood. Anything that impairs blood delivery to the brain can cause a stroke. Fortunately, strokes are uncommon in companion animals, but they can and do occur.
Causes of Stroke
The effects of a stroke are caused by lack of normal oxygen delivery to the brain. When they occur in dogs, strokes can be associated with Cushing's disease (hyperadrenocorticism), Rocky Mountain spotted fever, diabetes mellitus, heart disease, kidney disease or thyroid disease. In rare cases, internal parasites can contribute to strokes. Most strokes in dogs are caused by an embolus, which is a blood clot that develops at a remote site and then travels through the circulatory system, eventually lodging in a smaller vessel and interrupting blood flow to the affected area. When an embolus becomes lodged in and obstructs an artery in the brain, it causes the surrounding tissue to die - a condition called "infarction."
Other causes of stroke in dogs include bleeding into the brain from ruptured cerebral blood vessels, clotting of blood within a cerebral artery and cerebral tumors. A stroke can occur when a fragment of fat or spinal cartilage becomes dislodged and trapped in brain tissue. Strokes can also occur in dogs whose brains did not develop normally and in dogs with inherited coagulation (blood-clotting) disorders. Blunt trauma to the head, and poisons such as rodenticides, have been known to cause strokes in dogs as well. Disseminated intravascular coagulation (DIC) is a condition known to cause both bleeding and infarction within the brain. Sometimes, strokes happen for no apparent reason. In most cases, the actual cause of a dog's stroke will never be determined.
Prevention of Stroke in Dogs
There is no known way to prevent strokes in dogs.
Continual supportive care and supervision are extremely important for dogs that have suffered a stroke. As long as the stroke is diagnosed and treated in a timely manner, a full recovery is possible.
The effects of a stroke are caused by lack of sufficient oxygen delivery to the brain. Two types of strokes occur in dogs: ischemic strokes and hemorrhagic strokes. Ischemic strokes occur when the blood supply to the brain is compromised, and the brain becomes deprived of oxygen, glucose and other essential nutrients. Hemorrhagic strokes occur when a blood vessel inside the brain bursts, causing abnormal intracranial bleeding. Regardless of the underlying cause, the symptoms of stroke depend upon the location and extent of bleeding from or blockage of cerebral arteries. While strokes in dogs are not common, they do happen. It is important for owners to recognize the signs of stroke, so that affected dogs can be treated promptly.
Symptoms of Stroke in Dogs
The symptoms of stroke almost always come on suddenly. Owners may notice one or more of the following signs when their dog is having a stroke:
Loss of balance
Lack of coordination (ataxia)
Paralysis (usually on one side of the body)
Vision impairment or loss (sudden onset)
Loss of bowel control
Other abrupt behavioral changes
Dogs at Increased Risk
There is no age, sex or breed predisposition associated with strokes in domestic dogs.
It was once thought that dogs did not have strokes. However, as veterinary science advanced, it became apparent that dogs indeed do experience strokes, in much the same way as people do. The signs of stroke in dogs are different from those in people, and in many cases canine strokes are confused with other brain disorders. Because the signs of stroke in dogs are so similar to those of other neurological disorders, veterinarians normally need to use advanced diagnostic techniques to confirm a stroke diagnosis.
How Stroke is Diagnosed in Dogs
A dog should be taken to a veterinarian immediately when it shows stroke-like symptoms. The veterinarian will perform a series of tests to rule out other possible causes of neurological signs. If no particular abnormality is identified quickly, additional tests will be necessary to determine whether or not a stroke has occurred. The dog will need to be hospitalized and stabilized while these diagnostic procedures take place.
Unfortunately, most strokes in dogs cannot be diagnosed simply by radiographs (X-rays) or routine blood tests. The only current way to accurately diagnose stroke in dogs is through brain imaging scans. These include computed tomography (CT/CAT scan) and magnetic resonance imaging (MRI). Most local veterinary clinics do not have the instruments necessary to conduct either a CT or an MRI. If a veterinarian suspects that a dog has had a stroke, the owner normally will be referred to a veterinary neurologist whose clinic has these specialized capabilities.
Other useful diagnostic tools include routine blood work (to identify systemic disease), arterial blood gas evaluation (to assess oxygenation of blood), coagulation profiles (to assess blood clotting parameters), skull radiographs (to identify fractures, especially in cases of trauma), blood pressure assessment, an electrocardiogram (ECG) (to detect heart rhythm irregularities) and analysis of the cerebrospinal fluid (a "spinal tap").
CT and MRI scans will almost always provide the information necessary to diagnose a stroke. They also will help the veterinarian determine what type of stroke is involved. An ischemic stroke occurs when the blood supply to the brain has been compromised (such as by a clot, embolus or other obstruction), while a hemorrhagic stroke occurs when a blood vessel inside the brain bursts. The treatment protocol will depend upon which type of stroke has occurred.
Dogs suffering from a stroke need immediate veterinarian attention. The goals of therapy are to minimize brain swelling (reduce intracranial pressure) and associated tissue damage, maximize oxygen delivery to the brain, treat any identifiable cause of the stroke and rehabilitate the dog physically. Once the cause of the stroke is determined, the treatment protocol can be determined as well. Early diagnosis and treatment dramatically enhance the outlook for a full recovery.
The most important form of treatment for a dog that has had a stroke is supportive, inpatient nursing care. The dog will be carefully and slowly rehydrated with appropriate intravenous fluids, if necessary. Recumbent patients will be kept warm and dry with soft, absorbent bedding that is changed frequently; their heads should not be placed below body level. They also will need to be turned regularly to prevent pressure sores, pulmonary (lung) congestion and urine scalding. Physical therapy is often recommended as well, and may include therapeutic massage. If the stroke was caused by an underlying systemic disease such as diabetes mellitus or Cushing's (hyperadrenocorticism), that condition must be treated.
A variety of drugs are available to help dogs suffering from a stroke, including sedatives (to address disorientation and ataxia), antiemetics (to address nausea and vomiting), anti-inflammatories (corticosteroids or nonsteroidal anti-inflammatory drugs [NSAIDs], to control swelling), anticonvulsants (to control seizures) and antibiotics (when infection cannot be ruled out).
Normally, dietary restrictions are unnecessary. Clinical signs usually improve within 48 to 72 hours of treatment, starting first with resolution of vomiting and restoration of mobility and coordination. Most patients return to normal within several weeks. Recurrence is rare, but it can happen. Unfortunately, permanent disabilities can happen as well.
Most dogs that survive the first few days following a stroke have a good prognosis for full or nearly-full recovery. The long-term outlook depends upon identifying, eliminating or at least controlling the underlying cause of the condition. If a dog displays signs of stroke, he should be taken to his veterinarian or to a nearby veterinary emergency clinic immediately.