Until recently, it was thought that strokes were very rare in domestic pets. In the last few years, with the advance and increased availability of more specialist tests, strokes are being recognised more often in pets. The thought of your pet suffering a stroke may be frightening – but you should not be alarmed as strokes are often not as debilitating in animals as they are in people. With appropriate care your pet may do very well.
A stroke or cerebrovascular accident is the term used for the signs shown by an animal when the blood supply to the brain is reduced. There are two types of stroke:
- Ischaemic stroke is caused by a sudden lack of blood supply to the brain and
- Haemorrhagic stroke (or bleeding within the brain) is caused by a burst blood vessel.
More than any other organ, the brain relies on a constant blood supply to bring oxygen and nutrients and to remove waste products. If the blood supply to the brain fails, brain function is severely disrupted (ischaemia) or parts of the brain destroyed (infarct) in a specific region of the brain fed by the affected artery.
The diseases causing ischaemic stroke can be broadly divided into those diseases causing narrowing of an artery (thrombosis) and diseases causing clogging of an artery by material coming from somewhere else in the body (embolism).
In haemorrhagic strokes there may be leakage of blood within the brain tissue itself (intraparenchymal haemorrhage) or between the brain and the skull (subdural or subarachnoid haemorrhage). The site of the bleeding depends on the location of the affected blood vessel.
The signs of strokes in dogs are often very different from those seen in humans. In human stroke victims a drooping face or total paralysis on one side of the body are common signs but these are rarely associated with stroke in dogs. More common signs include head tilt or turn, loss of balance, loss of vision, circling and falling. Cats are more likely than dogs to suffer seizures after a stroke. These signs are not specific for stroke and can be seen associated with other brain disease.
our vet may suspect that your pet has suffered a stroke from the signs your pet is showing. In order to make a definite diagnosis your vet will need to do some further tests including imaging your pet’s brain. In order to get a picture of the inside of the brain specialist scans such as CT (computed tomography) or MRI (magnetic resonance imaging) are needed. It is not possible to make this diagnosis using standard X-rays. These tests require that your pet be anaesthetised and this will also allow a sample of spinal fluid (spinal tap) to be taken to check for other potential diseases that could cause similar signs.
A diagnosis of stroke can be based on identification of particular changes in the brain and ruling-out other diseases that could mimic a stroke (inflammation or infection of the brain, bleeding from a brain tumour or a metastatic tumour spreading to the brain). Once the diagnosis of stroke has been made, further tests will be needed to look for potential underlying causes for the stroke.
Ischaemic strokes have been associated with many medical conditions in dogs: kidney disease, heart disease, over-active thyroid glands, migrating worms (cuterebra), and high blood pressure(hypertension). Other less common causes of blockage of the blood vessels supplying the brain include clogging by a fragment of tumour, fat, parasites or spinal cartilage. Despite thorough investigations, an underlying cause is often not found.
Haemorrhagic strokes can be seen with diseases that interfere with blood clotting (some rodent poisons (warfarin-like products), immune-mediated thrombocytopaenia, and congenital clotting diseases), disease causing high blood pressure (kidney disease, heart disease, Cushings or thyroid disease), inflammation of the arteries (vasculitis) or abnormal development of the blood vessel in the brain.
Other causes of bleeding in the brain include head trauma, bleeding from a brain tumour or from a tumour spreading to the brain.
Once a stroke has occurred there is no specific treatment that can repair the damage done to the brain. Efforts should be concentrated on identifying a potential cause for the stroke and, if a cause is found, treating it to prevent further strokes. Good nursing care is essential for recovery.
Although there is no specific treatment for stroke, most dogs tend to recover within a few weeks. However recovery may not be possible if the stroke has affected a vital part of the brain. The long-term outlook and chances of another stroke depend on what has caused the stroke and whether this can be treated.