Synonymous :

Cerebral Vascular Accident (CVA)
Cerebral Thrombosis
Brain Attack

Definition

A stroke is a sudden disruption of circulation in the brain in one or more blood vessels. The impaired circulation results in a decreased flow of oxygen to the brain causing death of cells, resulting in loss of brain function with possible loss of consciousness, and other neurological impairments.

Clinical Signs

Clinical signs will vary depending on the type of stroke, the cause of the stroke, and how much damage has occurred to the cells of the brain. Any of the following signs may be seen:

• Sudden onset of seizure activity
• Extreme lethargy
• Irregular, abnormal breathing
• Difficulty with coordination and movement as indicated by the following:
  • Abnormal sensation in affected side (may eat out of one side of mouth).
  • Dysphagia (difficulty swallowing; has to work hard to move food to back of mouth with tongue).
  • Paralysis (often affecting only one side, but may affect both sides in brain stem strokes).
  • Difficulty sitting or standing on hind legs without leaning or falling to one side. May prop self up to eat.
  • Head tilt as seen with other signs of stroke (not to be confused with ear infection where this is the primary clinical sign).
  • Muscle spasms.
  • Loss of bladder/bowel control.
• Unequal pupil size (pupil may be larger on the side of paralysis)
• Micro-hemorrhages observed in eyes
• Blindness
• Change in behavior (e.g., irritability, or seeks attention)
• Coma
• Death

There are two types of strokes: Ischemic and hemorrhagic.

Strokes caused by a blockage in a cerebral vessel (Ischemic stroke) typically affect just the area of the brain that the vessel would have perfused. Clinical signs that come on suddenly and seem more severe may reflect an embolic stroke. Clinical signs that come on more gradually tend to be caused by a thrombotic stroke.

If the stroke is caused by bleeding (hemorrhagic stroke) the area affected can be greater. This is because the damaged vessel may continue to leak blood which then acts as a space-occupying mass placing increased pressure on the brain. Blood from a hemorrhagic stroke can also cause irritation to and scarring of brain tissue which can lead to the development of seizures.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

The development of a stroke is often the result of other underlying vascular diseases. A stroke results when cerebral blood vessels bringing oxygen and nutrients (glucose) to the brain rupture or are blocked by a clot or other mass. This blockage or disruption in the vessel results in damage or death to tissues and cells in that area of the brain it supplies. As brain and nerve cells die in the affected area, those parts of the body controlled by those cells can and do suffer temporary or permanent loss of function. Death can result if the stroke severely affects the body’s vital organs.

A sudden focal loss of neurologic function lasting a few minutes to one hour with complete recovery is referred to as a transient ischemic attack (TIA). Transient ischemic attacks result from a brief period of inadequate perfusion in one of the brain’s arteries or branches. A TIA or series of TIAs can increase and forebode the risk of impending stroke.

A stroke is usually brought about by one of four of the following events:

• Thrombosis: a clot forms in the blood vessel of the brain.
• Embolism: a clot travels from another part of the body to the brain.
• Compression of a blood vessel in the brain (e.g., caused by tumor or edema [fluid build-up]).
• Rupture of a blood vessel in the brain that leads to bleeding in the spaces surrounding brain cells.

In rats that have suffered a stroke, thrombosis and cerebral hemorrhages occur more often in the occipital area of the cortex and subcortex. Studies have also indicated that lesions have been noted in other areas of the brain such as the frontal and medial cortical areas and basal ganglia.

The risk factors for stroke development may include:

• Obesity
• Metabolic diseases (e.g., diabetes, Cushing’s Syndrome, kidney disease, hypothyroidism)
• Age
• Genetics
• Tumor blockage or bleeding from tumor into brain
• Leukemia
• Cardiac disease
• Hypertension

Rats experiencing a stroke may become alarmed or surprised by the sudden lack of coordination, loss of mobility, and/or loss of sensation. Some rats may attempt to reach their owner, or cling to their owner, for comfort and safety. Others may experience increased irritability with being handled or simply become lethargic. It is important for the pet owner to remain calm, approach gently, and speak softly to their rat. Prognosis will depend on the severity of the stroke, presenting clinical signs, the overall health of the rat, and diligent nursing care. Because it can be difficult to determine the underlying cause of the stroke, rats having had a stroke are at greater risk of having the damage extend or having additional strokes. However, it is possible for the pet rat to recover from a mild stroke. Even with partial paralysis, or loss of coordination, rats surviving a stroke can continue to have good quality of life with care provided by their owner.

It is important to note that other neurological disorders can often mimic the signs of a stroke, and should be ruled out by the veterinarian when assessing.

Some examples include:

• Brain tumor or Pituitary tumor.
• Subdural hematoma (a collection of blood between the brain and the skull) as may occur in a fall from a significant height.
• Brain abscess (a collection of pus in the brain caused by bacterial or fungal infection).
• Viral infection of the brain (encephalitis).
• Dehydration (resulting in an imbalance of sodium, calcium, or glucose).

Diagnostics

While a CT scan is helpful, this is not always practical with rats.

An X-ray of the skull may help to rule out mass formation.

Ophthalmoscopy may identify signs of hypertension if changes in retinal arteries are present.

Treatment

Treatment is based on alleviating clinical signs that may be present and any underlying disease. Diligent nursing care can help to improve the rat’s quality of life.

The following medications may be instituted by the veterinarian where clinical signs dictate:

• Oxygen to prevent hypoxia.
• Diuretics such as Lasix to control swelling in the brain or where underlying kidney disease is a contributory factor.
• Corticosteroids such as dexamethasone or prednisone to decrease inflammation of irritated tissue.
• Anticonvulsants such as Phenobarbital to decrease or alleviate seizure activity.

For information regarding individual medications refer to the Rat Medication Guide.

Nursing Care

• Doing gentle physical therapy on the rat may help to prevent atrophy of the muscles. Provide passive range of motion gently to reduce stiffness in paralyzed limbs.
• Reposition rat frequently to help prevent sores from developing on those areas of the body with limited mobility.
• Provide one level cage to prevent injury and provide easy access to water and food.
• Provide adequate soft bedding to help prevent sores on bony prominences from inadequate mobility.
• Keep cage clean to prevent skin breakdown.
• Assist rat with grooming and cleaning as needed.
• Administer medication as prescribed by veterinarian.
• Provide additional warmth to maintain body temperature within normal limits. It is essential that the rat does not become overheated or dehydrated. The rat should also be able to move away from the heat source if it becomes uncomfortable. If the rat is unconscious or immobile extreme care must be taken to keep the heat low and stable.
  • You can use an isothermic product that is heated in the microwave such as SnuggleSafe®. Make sure to follow the product directions carefully and wrap in a towel before placing in the cage. SnuggleSafe® will provide heat for 12 hours before needing to be reheated. Other similar types of products may vary in re-heat time. Check directions for individual product.
  • If using a heating pad (good for long term use) use only the low heat setting, put a thick towel in between the pad and the cage bottom, and place beneath a corner of the cage.
  • If none of these options are available you can use a plastic bottle filled with hot water, and wrapped in a towel, in the corner of the cage.
• Assess nutritional status:
  • Provide fluids to prevent dehydration. If the rat is willing to drink on its own or by syringe (using needless syringe), the following are suggested: fresh water, or a glucose mixture of 3 teaspoons of honey in 1 pint of warm water (be sure water is warm enough to dissolve honey and then cooled just enough so as not to burn rat’s mouth), or Jell-O water , or electrolyte replacement drinks such as Pedialyte or Gatorade which can be found in local grocery stores. Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and thawed as needed.
  • Care should be taken to prevent aspiration when giving fluids with an oral syringe. If the rat is not drinking discuss providing warmed SQ fluids with your veterinarian.
  • Assist with nutrition as needed to prevent aspiration. If the rat is unable to eat on its own, provide feeding of softer, puree foods and / or baby foods in an oral needless syringe every 2 hours being careful to prevent aspiration. Providing small amounts of food in this fashion will help to promote intestinal motility during illness. Include multi-vitamin supplement (can be found in pet store) if food intake is poor.
• Maintain seizure precautions by keeping rat in an area safe from injury (falling, bumping or running into cage objects).
• Administer oxygen if needed to prevent hypoxia.

Outcomes

• Maintains open airway, breath sounds normal, breathing pattern normal
• Anxiety is decreased
• Awareness improves
• Signs of seizure activity absent, or controlled with medication
• Skin integrity intact
• Nutritional status adequate
• Maintains hydration
• Perianal area kept clean and dry
• Bladder function normal
• Urethra kept clear of vesicular plugs (“penis plugs”)
• Mobility improves

Prevention

• Maintaining a healthy weight for the rat by preventing obesity through good nutrition.
• Learning the normal appearance of the rat, doing regular health checks to detect any changes in appearance of eyes, ears, teeth, coat, body, urine or fecal output or gait, and addressing any health concerns early on with a veterinarian can aid in prevention.

References

1. Dungworth, D., Mohr, U., & Capen, C. (1993). Pathobiology of the Aging Rat, Vol. 2. Washington DC: Intl Life Sciences Inst. Pgs 14-16
2. Henning, E., Warach, S., & Spatz, M. (2009). Hypertension-induced vascular remodeling contributes to reduced cerebral perfusion and the development of spontaneous stroke in aged SHRSP rats. J Cereb Blood Flow Metab., (Dec 2).
3. Suckow, M., Weisbroth, S., & Franklin, C. (2005). The Laboratory Rat, Second Edition (American College of Laboratory Animal Medicine). Toronto: Academic Press.
4. University of South Florida Health Sciences Center (2005, July 1). Antioxidant-rich Diets Reduce Brain Damage from Stroke in Rats. ScienceDaily. Retrieved February 11, 2010, from https://www.sciencedaily.com/releases/2005/07/050701065550.htm
5. Additional resources used for this article listed in References of the Health section of the Rat Guide, https://ratguide.com/health/reference/references.php