HIGH BLOOD PRESSURE IN CATS IS SERIOUS It's an all-too-familiar scenario for the experienced veterinarian: A worried cat owner comes into an animal hospital with a cat who has suddenly lost his eyesight. After a thorough examination, the veterinarian makes a diagnosis: hypertension, or high blood pressure. Like humans, cats may suffer from one of two types of hypertension: primary or secondary. Primary hypertension is caused by the cat's dietary habits or a genetic predisposition to the disease. It is extremely rare in cats. Secondary hypertension is caused by an underlying disease such as hyperthyroidism, renal (kidney) failure, or an enlarged heart. Most cats with high blood pressure have secondary hypertension. Pharmacological Treatments The drugs that may be prescribed to treat feline hypertension fall into four major categories, all of which will sound familiar to humans being treated for hypertension:
Sudden blindness is a symptom Among cats, the most common symptom of hypertension is blindness in one or both eyes. Hypertension causes blindness because ten consistently high blood pressure literally bursts the tiny, delicate blood vessels deep within the cat's eye, especially those bringing nutrients to the retina, the part of the eye that contains the light receptors. These bursting blood vessels often cause the retina to become detached as well. Reciprocal relationship Hypertension, hyperthyroidism, and renal disease have a complex cause-and-effect relationship. Consequently, one of the first things that a veterinarian will do' with cats experiencing sudden blindness is test for hypertension. The common method of testing for hypertension is to measure the cat's blood pressure. (This is usually accomplished using an ultrasound sensor and cuff on one of the limbs.) If hypertension is detected, the veterinarian will conduct tests for hyperthyroidism (see CatWatch, December 1997) or renal disease (see CatWatch, January 1998). Similarly, if a veterinarian diagnoses hyperthyroidism, chronic renal failure, or an enlarged heart in a cat, he or she will be likely to check for hypertension. If a cat becomes blind as a result of hypertension, his chance of recovering his eyesight is fair to good. However, cats who become blind because of severe hypertension usually have a poor prognosis and often the loss of vision is permanent. "The reason for the difference is that cats with really high blood pressure tend to hemorrhage into many ocular structures, not just the retina," says Thomas Schermerhorn, VMD, of the College of Veterinary Medicine at Cornell University. Restrict dietary sodium In most cases, managing a cat's hypertension begins with the dietary restriction of sodium, salts that may cause water retention and thus increase the blood pressure. "However, for the majority of cats, dietary management won't work as the sole therapy," Dr. Schermerhorn says. "Addressing or correcting the underlying problem is extremely important in managing feline hypertension. So if the condition is caused by renal failure, you must treat that disease. If the cat has hyperthyroidism, definitive treatment of that condition will typically cure the hypertension as well." If hypertension persists despite dietary management and treatment of the underlying disease, your veterinarian can prescribe drugs that will lower your cat's blood pressure. 
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