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Hypertension in Cats
Contributing Factors
Clinical Signs
Causes
Diagnosis
Treatment
Prognosis
Hypertension is the term for high blood pressure.
Contributing Factors
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In humans, hypertension is related to several factors, including a stressful lifestyle. Although not all the causes of feline hypertension have been identified, stress does not appear to play a role in the development of this disorder in cats. However, kidney disease and thyroid disease are known to be associated with feline hypertension and will be described in more detail below.
Clinical Signs
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As with people, many cats with hypertension have no symptoms at all, especially if the hypertension has not been long-standing.
In cats who are symptomatic, vision abnormalities are the most common clinical findings. These abnormalities can include dilated pupils that do not constrict with light, blood within the front chamber of the eye, and blindness. Blindness develops because high blood pressure in the eye causes the retina to detach. These cats run into objects in their path because most of them have no vision at all.
Other clinical signs or symptoms that may be seen with high blood pressure include strokes, blood clots, heart murmurs, and general lethargy. If cats with high blood pressure also have concurrent kidney or thyroid disease (both of which can be contributing factors in hypertension), they may also have signs referable to pathology of those two organ systems (see below).
Causes
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Kidney failure and hyperthyroidism have been identified as the two most common predisposing factors for development of feline hypertension. Cats may also have primary or idiopathic hypertension in which case there is no apparent underlying cause.
Kidney disease. It appears that several different mechanisms may lead to development of hypertension in cats with kidney disease. One theory suggests that as a cat ages, the kidneys undergo normal aging changes, including a slow accumulation of scar tissue. With time, this scar tissue causes the kidneys to shrink in size. When the kidney shrinks due to the accumulated scar tissue, it is harder for the blood to filter through. Because the kidneys normally receive 20% of the blood with every heartbeat, blood backs up into large arteries and leads to an increase in blood pressure. One study found that about 65% of cats in old-age kidney failure have hypertension. Even elderly cats in the early stages of kidney disease may also have hypertension.
The most common clinical signs seen with kidney disease include an increase in water intake and urine output, dull coat, weight loss, and vomiting.
Hyperthyroidism. As in people, the thyroid gland is located on the underside of the neck and plays a very important role in regulating the body's rate of metabolism. Hyperthyroidism is a disorder characterized by the overproduction of thyroid hormone and a subsequent increase in the metabolic rate. This is a fairly common condition seen in older cats. Although the thyroid gland enlarges, it is usually a non-malignant (benign) change. Less than 1% of hyperthyroid cases involve a malignant change in the gland.
Many organs are affected by hyperthyroidism, including the heart. The heart is stimulated to pump faster and more forcefully; eventually, the heart enlarges to meet these increase demands for blood flow. The increased pumping pressure leads to a greater output of blood and high blood pressure. About 80% of cats with hyperthyroidism have high blood pressure, although most of them do not have blood pressures high enough to cause blindness.
The most common clinical sign seen with hyperthyroidism is weight loss, often in the face of a normal or even better than normal appetite. Other signs may include increase in water intake or urine output, unkempt coat, vomiting, diarrhea, constipation, behavior/personality changes, etc.
Primary hypertension. This means that there is no apparent underlying disease present.
Diagnosis
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Hypertension should be suspected in any cat with kidney disease or hyperthyroidism. Onset of sudden, unexplained blindness should raise a strong suspicion for hypertension and the associated diseases should be considered. Also, the presence of a heart murmur or kidney-related problems may signal the presence of a hypertensive state.
Because hypertension is now recognized as a common finding in geriatric cats, and we know that these cats may have no symptoms, we recommend annual blood pressure screening in all geriatric cats (12 years or older) and at any age and/or more frequently in cats with known kidney or thyroid abnormalities
Blood pressure is determined with a device that can detect blood flow in arteries. Because the cat’s arteries are so small, a special instrument is required. The most common one used is based on the Doppler principle.
Treatment
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The first step in treatment is to use one or more of several hypotensive agents (drugs to lower blood pressure). The next step is to diagnose and treat the underlying disease. If it is hyperthyroidism, treatment is required. When treatment is completed, hypertension resolves, and further treatment with hypotensive drugs is not needed. If kidney failure is diagnosed, it is usually not curable but often can be controlled. However, most of these cats require long-term treatment for hypertension. If no underlying disease is found, primary hypertension is considered to be present and long-term treatment for hypertension is needed.
Drugs used to treat hypertension in cats are similar to those used in people, and include calcium channel blockers, ACE inhibitors, diuretics, etc.
Prognosis
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The underlying disease that caused hypertension to develop must be cured or controlled. Long-term success depends on whether or not this is possible. If the cat has kidney, heart, or thyroid disease, it is important to treat those aggressively. Hyperthyroidism is curable, but old-age kidney failure is not. However, many kidney failure cats can be managed successfully for months to years.
If the cat has blindness due to detached retinas, a medical emergency exists. Preservation or return of vision may be possible, but only if treatment for high blood pressure is instituted promptly. If the retinas remain detached for several days, the prognosis is poor for a return of normal vision. Therefore, the key to a successful outcome is rapid diagnosis and early administration of the proper medication to lower blood pressure.
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