Case study: Sally - Progressive Retinal Atrophy (PRA) in cats

Sally

 Sally is a 3-year-old Abyssinian cat that was rescued from a hoarding situation. She was one of 84 cats rescued. Eighty of the cats in the household were too ill or debilitated to survive and had to be euthanized. After adoption, it was discovered that Sally was Feline Leukemia positive. She is shy, but sweet, and her owners brought her in to us because she suddenly appeared to lose her sight. She began bumping into things and lost her fear of the dog. If you notice in her photo, her pupils are very dilated, and her owners had noticed this at home, too. Her regular veterinarian sent her to us because high blood pressure was suspected.

What does high blood pressure have to do with eyesight?

The retina lines the back of the eye

The retina is a thin membrane lining the inside of the eye that receives light and translates it into electrical impulses for the brain with special cells called photoreceptors. There are two kinds of photoreceptors - rods that process black and white or dim light vision and cones that process colors or bright light. If the retina or its photoreceptor cells become damaged in some way, the eye has trouble converting waves of light into signals that the brain can understand, interfering with a cat's vision.

 One of the ways that cats can lose their vision is by developing hypertension lesions in the retinas - tiny blood vessels are damaged and regions of the retina lose their ability to function as they lose their blood supply. These lesions look like bubbles in the retina. If a cat's blood pressure remains elevated for a long period of time, the retina can completely detach and lose its connection with the nerves that transmit visual impulses to the brain. Once this has happened, a cat becomes irreparably blind. If the hypertension is diagnosed and treated early, as in these photos, the retinal lesions can heal over time.

Retinal lesions appear like bubbles in the back of the eye

The same eye 2 months after starting blood pressure medication

 Notice that not only are the lesions gone, but the blood vessels appear more visible.

The first thing that we did when Sally came in was check a blood pressure reading. Her blood pressure was 150mmHg, which is a normal pressure in a nervous cat. Hypertension was not the culprit in this case. So, what could be the problem?

The next thing that happened was that Sally received a full physical exam from Dr. Demos, including an eye exam. This is what Dr. Demos saw when she looked in Sally's eyes...

Something very important is missing, here!

There are no blood vessels in this retina!
This is a characteristic feature of something called Progressive Retinal Atrophy (PRA). PRA is a recessive trait in certain breeds of cats such as the Abyssinian, the Somali and the Ocicat. Perisans and Siamese are also often at risk. There are a number of other breeds that have also been identified to carry the mutated gene in small numbers.

Other key features of this disease are a granular appearance to the retina, signs of retinal thinning, and a reduction or thinning of blood vessels. Increased reflectivity of the retina and dilation of the pupils are symptoms that owners can easily see at home. Later stages show pigment changes to the retina and a degradation of the optic nerve. These changes usually happen equally to both eyes at the same time.

Sally's pupils stay dilated, even in bright light

The most common form of PRA in cats is involved a progressive degeneration of the rod and cone receptors in the retina.The cat's eyes develop normally as a kitten, but as the cat gets older, the cat will begin to experience night-blindness and may tend to avoid stairs or darkened areas of the home. It will progress to total blindness by the age of 3-5 years. This is problematic not only for the cats themselves, but for the breeders of high-risk breeds, because often the disease is not apparent until after the age at which many cats have already participated in a breeding program. If you are interested in a purebred cat, it may be a good idea to ask your breeder about PRA and whether their cats have been genetically tested for the mutation.

Unfortunately, this is a problem for which there is no treatment. However, the good news is that cats adapt well to being without their sight due to their superior hearing, sense of smell and sense of touch (whiskers). You can read about the amazing cat, Homer, who caught flies out of the air without the aid of sight!

If your cat starts to show reluctance to move around at night, or has trouble jumping onto furniture, or starts to bump into things, it would be a good idea to have your cat's eyes checked by his or her veterinarian, as well as having a blood pressure exam performed.

Feline Hypertension: What you need to know

High blood pressure? In a cat? All your cat does is lie around all day, grooming himself and sleeping - he couldn't possibly have high blood pressure, right?

Wrong!
In humans, we think about high blood pressure as a problem of high-stress, high-anxiety people with high-pressure jobs. According to the American Heart Association, however, science has not definitively proven that stress causes high blood pressure, even in humans. It is more likely that people under stress will engage in unhealthy activities that ARE linked to high blood pressure - such as smoking, drinking too much alcohol, and eating an unhealthy diet or not exercising regularly.

Unlike human high blood pressure, feline hypertension is not usually a stand-alone disease. It is most often seen associated with another illness, such as kidney disease or hyperthyroidism. However, in cats that have kidney disease, it is often uncertain whether the kidney disease caused the hypertension or chronic hypertension damaged the kidneys.

Symptoms: Just as in humans, there are few, if any, outward signs of high blood pressure in cats.

The "bubbles" in this photo of the inside of a cat's eye indicate areas where the retina is detached due to chronic high blood pressure

The most common sign of high blood pressure, and the one most recognizable by owners, is sudden blindness. Blood vessels under high stress in the eye are at high risk for rupture or leakage, which damages the retina. Over time, this can lead to complete retinal detachment and complete blindness.

Some cats with high blood pressure will develop a heart murmur or a "gallop" rhythm due to damage to the heart - most commonly a thickening or overgrowth of the muscle of the left ventricle.

Sometimes people who start treating their cats for their high blood pressure notice a change in their cat's behavior (for the better!), noting that they seem less anxious, or they have stopped howling at night, or they appear more active.

It is known that in humans, high blood pressure can cause headaches. This is very difficult to diagnose in cats, however, we know that cats experience pain in a similar manner to humans, so one might wonder if cats with high blood pressure also experience headaches.  If so, diagnosing and treating high blood pressure would relieve your cat of head pain.

Other outward signs and symptoms that may appear with high blood pressure are associated with the primary disease that is linked to the hypertension: increase in water intake and urine output, dull coat, weight loss, change in appetite (either eating more or eating less), vomiting, diarrhea, constipation, and behavior or personality changes.

Inwardly, chronic high blood pressure can lead to organ damage.
65-100% of hypertensive cats have decreased kidney function
50-70% of hypertensive cats have damage to their hearts
30-40% of hypertensive cats have damage to their retinas which can ultimately lead to blindness if left untreated
15% of cats with high blood pressure have neurologic signs including head-pressing, twitching or seizures

Prevalence and Risk Factors: The cats that are at highest risk for high blood pressure are senior cats, especially those over the age of 10 or those with other health conditions. There does not seem to be a specific breed that is at high risk for high blood pressure. 

High blood pressure in older cats appears to be fairly common, especially as a secondary problem associated with other diseases. Exactly how common is still up for debate. In researching for this article, many studies disagreed about the numbers, and most of the studies were performed with 100 or fewer cats - but we do know that hypertension is a serious issue that we can easily diagnose and treat.

Somewhere between 20-65% of cats with chronic kidney disease have hypertension.
Somewhere between 9-23% of cats with hyperthyroid disease have hypertension.

Somewhere between 17-50% of cats with high blood pressure have hypertension that is not associated with another problem.

Diagnosis: High blood pressure in cats is diagnosed with a blood pressure reading, very similar to the readings taken in humans. While oscillometric (electronic, automatic) blood pressure machines exist and are quite accurate in humans and dogs, the Doppler method of blood pressure examination is generally recommended as the most accurate in cats. The oscillometric units are often unable to detect feline blood pressure (in up to 52% of cases!), take longer to get a result, were less precise and often read lower than the actual pressure.

Checking a blood pressure with the Doppler method is painless and most cats are quite calm and unconcerned by the process. After the cat has time to acclimate itself to the exam room, the technician attaches a small cuff (the same kind that is used in human neonatal medicine) to one of the cat's legs. Preferably, the cat's owner is present to calm and hold the cat for the technician, but occasionally, just like small children, a cat may behave better for a group of strangers than in front of his or her "parents", or they may feed off an owner's anxiety and become anxious, themselves.

A small amount of alcohol is applied to the cat's foot or a small amount of hair is shaved near the paw pad, and then ultrasound gel is applied to the Doppler probe and is it gently pressed against the cat's foot. The Doppler machine is turned on, and the heartbeat becomes audible  as a "whoosh whoosh" noise. Every effort is made to keep the cat calm and relaxed during this process, to avoid artificially raising the blood pressure. Several readings are taken and the average of these readings is recorded.

Doppler blood pressure machine and supplies

 

The cat either reclines on its side for a rear leg pressure check or sits/lies in a normal position for a front leg reading. In some cats, it may be appropriate to take a measurement from the tail.

The blood pressure cuff is wrapped around the leg, and some alcohol is used to wet the fur. In some cases, a small amount of fur is shaved near the cat's paw pad. Ultrasound gel is applied to the Doppler probe and then held gently against the foot. The blood pressure cuff is then inflated and several readings are taken.

Treatment:

Amlodipine is usually the medication veterinarians turn to for treatment of high blood pressure in cats. This medication relaxes the blood vessels to allow the blood to pass more easily. Most cats started on this medication are started on a low dose and then re-checked in a couple weeks to ensure that they do not need to have additional medication. This avoids adverse side effects from a sudden decrease in blood pressure such as weakness or fainting spells, but also allows for appropriate correction of blood pressure that is severely elevated within a short period of time. Other medications such as benazepril and atenolol may be preferable in some cases, depending on the cat's overall health.

Additionally, treating any primary disease such as hyperthyroidism, diabetes, kidney disease, may aid the control of high blood pressure.

Currently, Exclusively Cats Veterinary Hospital is participating in a nationwide study of an FDA-regulated investigational medication for high blood pressure associated with chronic kidney disease in cats. This clinical trial is designed to determine the effectiveness of the investigational medication in a real-world situation. We hope you will consider this opportunity to possibly help your cat and, potentially, many other cats nationwide. 

ANY CAT* over the age of 7 is currently eligible for a free exam and blood pressure screening. 

For more information, call our office at 248-666-5287 or visit www.mycatcanhelp.com.
To get involved, please call our office to schedule an appointment!


*Any cat that is not currently on blood pressure medication, and is not an F1 generation Savannah Cat or Bengal breed.


Selected Resources and References:
More information:
High Blood Pressure in Cats: Winn Feline Foundation
High Blood Pressure (Hypertension) in cats: FAB cats
Diagnosing Feline Hypertension: Pet MD
All About Hypertension: Tanya's Comprehensive Guide to Feline Chronic Kidney Disease
Hey, Doc, Why Did My Cat Go Blind? by Dr. Eliza Sundahl at Felinedocs.com

Research and Journal Articles:
Management of Hypertension in a geriatric cat: Canadian Veterinary Journal
Managing Hypertension in Cats with Hyperthyroidism: Proceeding of the SEVC

Southern European Veterinary Conference Oct. 2-4, 2009, Barcelona, Spain, Thomas K. Graves, DVM, PhD, DACVIM 

Prevalence of systolic hypertension in cats with chronic renal failure at initial evaluation. J Am Vet Med Assoc. 2002 Jun 15;220(12):1799-804. Syme et. al

Blood Pressure in Small Animals - Part 2*:Hypertension - Target organ damage,

Heart and Kidney, A.P. Carr, B. Egner

Feline Systemic Hypertension: Classification and pathogenesis, E Rosanne Jepson, BVSc (Dist) PhD MRCVS∗
Feline Systemic Hypertension: Diagnosis and Management, Rebecca L Stepien, BS DVM MS DipACVIM (Cardiology)⇓

Evaluation of Doppler Ultrasonic and Oscillometric Methods of Indirect Blood Pressure Measurement in Cats. Haberman et al. 2004.

 A comparison of CAT Doppler and oscillometric Memoprint machines for non-invasive blood pressure measurement in conscious cats. Jepson et al. 2005.
  The Prevalence of Ocular Lesions Associated with Hypertension in a Population of Geriatric Cats in Auckland, New Zealand. Carter et. al, 2013
Routine health screening: findings in apparently healthy middle-aged and old cats. Paepe et. al. 2013
Systemic Hypertension in Cats: Current Issues in Diagnosis and Therapy, AAFP 2011 Conference 9/9-9/11. Daniel F. Hogan DVM, DACVIM (Cardiology)