|
Most of us have some idea of what happens when someone has a stroke: they are going along normally and then suddenly a group of nerves suddenly does not work. This might involve inability to move certain muscles (arm, face, etc.) or it could involve deeper more crucial neurologic functions in such a way that the affected person dies. Most of us know that “stroke” involves some kind of blood clot plugging an important blood vessel in the brain, preventing an important area from receiving circulation. Most of us also know that sometimes the symptoms of the stroke are reversible or partly reversible but we do not know what separates the reversible stroke symptoms from the irreversible ones. In this discussion, we are going to be reviewing strokes and other vascular accidents in the brains of pets.
If you have come here seeking information regarding a dog or cat that has a head tilt to one side, perhaps falling toward that same side, and rapid back and forth darting of the eyes, you are in the wrong classroom. The subject you want to read about is Vestibular Disease, which is generally not caused by a vascular accident but is often incorrectly referred to as a “stroke.
Vascular accident is non-progressive after the first 72 hours.
There is actually more to a vascular accident than a blood clot lodging or forming in an inappropriate place. Other vascular accidents include a small area of bleeding in the brain, a small blood vessel tumor interfering with circulation, a temporary blood vessel spasm, or even an area of inflammation which alters blood flow. The bottom line is an area of the brain gets deprived of circulation (and thus of oxygen), the neurons (cells which make up the nervous system’s electrical wiring system) are injured or killed, and function is lost. What the function loss might look like is completely dependent on the area of the brain involved. Here is a list of some of the possible clinical signs (with an illustration of the four brain regions below the table):
|
Brain Region
|
Clinical Signs
|
|
Telencephalon
|
Change in mental alertness
Loss of certain eye reflexes on the side opposite the brain damage
Loss of sensation of the nose on the side opposite the brain damage
Weakness on the side opposite the brain damage
Circling towards the side of the brain damage
Drunken gait
Head pressing
Seizures
|
|
Thalamus or midbrain
|
Crossed eyes
Head tilt or turn towards the side of the brain damage
Postural defects
Loss of certain eye reflexes on the side opposite the brain damage
Back and forth eye movements
|
|
Cerebellum
|
Drunken gait
Loss of certain eye reflexes on the side of the brain damage
Head twisted backwards or upward
Measuring steps incorrectly
Tremors during intended actions
Back and forth eye movements
Head tilt
Rigid neck amd body
|
|
Brain stem: Midbrain, pons or medulla
|
Head and neck pain
Problems with the reflexes of the head and face
Altered states of consciousness
Weakness in all four legs
Postural defects
Head tilt and back and forth eye movements
|
|
As far as human patients go, most of us are familiar with the risk factors as they are emphasized in assorted public service announcements: smoking, diabetes mellitus, high blood cholesterol levels, alcohol use, and history of heart attack. Most of these problems are simply not relevant to pets which makes vascular accident a much less common condition in pets (whereas stroke is the third most common cause of human death after heart disease and cancer).
In dogs, the most common factors increasing risk of vascular accident are:
Cushing’s Syndrome
and
Chronic Kidney Failure
Other risks include Heartworm Disease, particularly if a larval heartworm gets lost during migration and ends up in the brain (an example of “aberrant migration”). Also, the use of phenylpropanolamine, a medication removed from the human market because of increased stroke risks, is still common in dogs as treatment for urinary incontinence. This medication has been implicated, albeit rarely, in cases of canine vascular accident.
In cats, common underlying diseases would be:
Hyperthyroidism,
Hypertrophic Cardiomyopathy,
and
Chronic Kidney Failure
Diabetes mellitus probably deserves at least an "honorable mention" as well.
The pet with sudden neurologic symptoms could very well be a victim of vascular accident but may also have suffered some other condition such as: head trauma, metabolic disease, poisoning, cancer, or even infection or inflammation. Vascular accidents are characterized by sudden onset which may progress over 24-72 hours, followed by slow recovery or partial recovery. (Of course, death is possible if the initial injury is severe enough and in that event obviously recovery is not possible, slow or otherwise.) Accidents involving bleeds tend to be more severe than those involving obstructive clots as they involve larger areas of the brain. Fortunately for dogs (and unlike the situation in humans), bleeding accidents ("hemorrhagic stroke" as from an aneurism) is far less common than clotting accidents ("embolism" or "thrombosis'). The first step is going to be basic metabolic blood and urine testing plus a measurement of blood pressure. Other tests may be indicated depending on the patient’s specific history and the initial test findings. Ultimately, MRI (magnetic resonance imaging) is needed to detect hemorrhage, blood clot, or simply damaged areas of the brain. Radiography is not adequate as imaging of the brain tissue through the skull bones is not really possible with this technique. CT (formerly called “CAT scanning”) is not as sensitive in its ability to pick up blood clots and damaged brain areas but is a fair second choice if MRI is not available. A blood test detecting a protein called a "D-dimer" is useful in determining whether or not an abnormal blood clot is being addressed in the body, the D-dimer being the by-product of a blood clot disintegrating
Treatment of vascular accident is all about supportive care: maximizing brain oxygenation until the damaged nerves can heal. If seizures are occurring, they must be suppressed with medication. If pressure inside the skull is elevated, it must be normalized. High blood pressure must be corrected as must abnormal bleeding states. Prolonged intensive nursing care should be expected. Oxygen supplementation and tube feeding for nutrition may be needed. The pet may even require a ventilator to maintain respiratory function.
At this time more specific treatments are considered experimental. Calcium channel blockers, amlodipine in particular, appear to be protective to neurologic tissues if administered in the first six hours after the event. Low doses of aspirin have been protective against stroke recurrence in humans, though animal studies are lacking. This may be a treatment your veterinarian employs for the pet suffering from vascular accident. Antioxidants such as SAMe, make logical sense but controlled studies in animals have not been performed.
In humans, the degree and speed of recovery depend on: the size of the brain area involved, location of the brain area involved, cause of the vascular accident, and progression of the clinical signs after the initial event. In a study of 33 dogs with vascular accidents, none of these things correlated with outcome. Instead, dogs that had known underlying diseases (i.e. where the cause of the vascular accident was known) had shorter survival times and increased risk of recurrence. As a rule, pets are felt to have higher potential for recovery than humans (with recovery times typically measured in days to weeks).
The pet is likely to have poor mobility at home and require special care (click here for suggestions for caring for pets with poor mobility).
Page last revised: 12/28/2012
|
