VASCULAR ACCIDENT IN THE BRAIN

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. (In fact, "stroke" is the third most common cause of human death after cancer and heart disease.). 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. 

(original graphic by marvistavet.com)

IS A VASCULAR ACCIDENT THE SAME AS A “STROKE”? Vascular accident is non-progressive after the first 72 hours. The short answer is that stroke and vascular accident are the same thing but 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 on the left):

FACTORS INCREASING RISK

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 than it is in humans. That said, an underlying disease can be found in approximately 50% of dogs with vascular accidents and 30% of dogs with vascular accidents will have high blood pressure.

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. Additional causes include: atherosclerosis (cholesterol plaques like humans get) associated with hypothyroidism, hypertriglyceridemia (elevated blood fat levels) in miniature schnauzers, and cancer.

(Photocredit: Morguefile.com)

In cats, common underlying diseases would be: Hyperthyroidism, Hypertrophic Cardiomyopathy, and Chronic Kidney Failure Diabetes mellitus cancer, migrating heartworm larvae, and migrating Cuterebra (a special type of fly) larvae probably deserve at least an "honorable mention" as well.

(Photocredit: Morguefile.com)

HOW TO TELL IF THERE HAS BEEN A VASCULAR ACCIDENT

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. Thromboelastography (TEG) testing is another blood test that can also be used to help distinguish a vascular accident from some other type of neurologic condition.

TREATMENT

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. Patients can be affected such that they need special home care such as help with mobility and toilet function. Physical therapy may be helpful in regaining function. Some patients, however, are so compromised that they need intensive nursing in the hospital at least temporarily. This could include a feeding tube, supplemental oxygen or even a ventilator to assist breathing depending on how much loss of function has occurred.

Treatment of the vascular accident patient is basically supportive; there is no specific treatment as yet supported by scientific evidence and investigation. There are, however, many treatments that might be employed based on theory. Calcium channel blockers, amlodipine in particular, appear to be protective to neurologic tissues if administered in the first six hours after the event. Antioxidants such as SAMe, make logical sense but controlled studies in animals have not been performed. Hyperbaric oxygen therapy has been advocated to improve oxygenation of compromised brain tissue so as to minimize the area of permanent damage.

RECOVERY

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).

ADDITIONAL INFORMATION:

For a list of products that assist mobility and management of patients with poor mobility click here.

To find a veterinary neurologist: Enter your city or zip code and select "NEUROLOGY" in the specialty box at:

http://find.vetspecialists.com

To find a pet physical therapist in your area:

www.caninerehabinstitute.com/Find_A_Therapist.html 

Page last revised: 2/25/2024