Managing chronic diseases in cats

The pet cat population in the United States exceeds the pet dog population, yet the average cat visits the veterinarian only half as often as the average dog.1 Conversely, advancements in feline health care offer us more opportunities to maximize cats' long lives. It's our job to make sure cats receive routine care.

Susan Little, DVM, DABVP

Diagnosing and treating chronic health conditions is one of the most rewarding areas of feline health care. By learning to recognize and treat these conditions, you will deliver higher-quality medicine. The satisfaction of practicing good medicine motivates both veterinarians and support staff members, and clients will feel more bonded to your practice. Here's a look at the most common feline chronic illnesses and recent medical advances.

Obesity

It has been estimated that 25% to 33% of cats are either overweight or grossly obese (

Figure 1

).2 Yet the 2003 AAHA Compliance Study3 found that veterinarians significantly underdiagnose feline obesity. Cat owners may not recognize obesity or know about the associated health risks, which include diabetes mellitus, hepatic lipidosis, lameness, lower urinary tract disease, and other health problems.

Figure1. Obesity is one of the most common feline diseases, affecting at least 25% of pet cats.

For many feline patients, managing obesity is a lifelong issue. Quantifying obesity is the first step to help both you and the owner recognize the problem. Cats are considered overweight when they are 10% above optimal body weight and obese when they are 20% above optimal weight. Weigh feline patients at every visit and record their body condition scores using a chart such as the Purina 9-point Body Condition System. Optimal body weight is correlated with a score of 5 using the Purina system.

As we better understand cats' nutritional needs, we're better able to prevent and treat feline obesity. For example, we know that carbohydrate-rich, energy-dense diets contribute to feline obesity. Energy-restricted diets may lead to weight loss—but often at the expense of lean body mass. Many veterinarians and cat owners have been frustrated by the poor success rate of traditional high-fiber, low-calorie weight loss diets.

On the other hand, cats receiving high-protein, low-carbohydrate diets can lose weight and maintain lean body mass. Some commercial diets, such as Hill's Prescription Diet m/d, offer high-protein, low-carbohydrate formulations designed for weight management. Research also supports the administration of carnitine at 250 to 500 mg/cat/day in addition to dietary therapy to enhance fat metabolism and weight loss.2,4 Carnitine supplementation is continued for as long as needed to achieve and maintain optimal body weight.

A successful weight management plan starts with calculating the cat's daily food requirement using the manufacturer's feeding guide based on the target body weight. If the cat doesn't lose weight within one month, reduce the daily portion by 10% to 15% until the cat starts losing weight. Schedule regular re-evaluations to monitor progress and encourage owners to keep a diary of the diet type, amount fed, and body weight over time. Many obese cats will require up to 12 months to reach their target weight safely, so remind owners that patience and commitment will increase their chances of success.

Your weight management plan should include suggestions for improving exercise by enriching the cat's environment. Food puzzles are toys that release small amounts of dry food as the cat plays, and they are a great way to provide a more stimulating environment and encourage cats to be more active. For more examples, visit the Ohio State University College of Veterinary Medicine's Indoor Cat Initiative Web site at www.nssvet.org/ici/index.php.

Diabetes mellitus

Diabetes mellitus is the second most common endocrinopathy in cats after hyperthyroidism, affecting about one in 200 to 300 cats.5 The typical diabetic cat is middle-aged to senior,

obese, and a neutered male. As we learn more about the nutritional management of diabetes mellitus and advances in insulin therapy and monitoring, we can better treat these patients.

Recent research has shown that a high-protein, low-carbohydrate diet similar to the cat's natural diet of mice may help control diabetes mellitus.5 Diabetic cats receiving low-carbohydrate diets were 10 times more likely to be able to discontinue insulin therapy than cats fed high-fiber diets in one study.6 Cats are obligate carnivores, and, as such, are not metabolically adapted to diets containing an excess of carbohydrates.5 Diets rich in carbohydrates may worsen hyperglycemia in diabetic cats and even cause protein wasting. Appropriate diet options for diabetic cats include canned kitten foods or newer therapeutic diets formulated for diabetic cats, such as Purina Veterinary Diets DM Diabetes Management and Royal Canin Veterinary Diet Diabetic DS 44.

Many insulins have been available over the years to manage feline diabetes. None have proved ideal for a variety of reasons, including inadequate duration of action, poor absorption, and variable patient response. Common insulin choices include NPH (Humulin N—Eli Lilly), protamine zinc (PZI Vet—IDEXX Laboratories), and porcine zinc insulin (Caninsulin—Intervet, available in Canada, and Vetsulin—Intervet, available in the United States).

Glargine (100 U/ml ) (Lantus—Aventis), a human synthetic insulin analogue, offers a new option. It's marketed for people as a long-acting, peakless insulin and it has a shelf life after opening of six months when refrigerated. Evaluations of the pharmacokinetics and pharmacodynamics have shown that glargine has a long duration of action and predictable blood glucose-lowering ability in diabetic cats.7

Start newly diagnosed diabetic cats on glargine at 0.5 U/kg subcutaneously every 12 hours and hospitalize them for the first two or three days of therapy.8 Perform daily blood glucose curves and obtain blood samples every four hours during hospitalization. Most cats' blood glucose levels will decrease substantially within three to five days, and they will need their glargine dosage reduced within two weeks. Reports of cats exhibiting clinical signs of hypoglycemia have been rare with this insulin. Cats fed a high-protein, low-carbohydrate diet and treated with insulin glargine have an excellent chance of diabetes remission within four months.9 Insulin glargine offers a promising new tool for treatment of feline diabetes mellitus and may become the insulin of choice as North American practitioners gain experience with its use.

Blood glucose curves are essential in managing feline diabetes, yet cats may be stressed during hospitalization, making it difficult to interpret results. One solution is to teach clients how to perform blood glucose curves at home using capillary blood sampling from the ear and a portable blood glucose meter (Figure 2). VeterinaryPartner.com offers an excellent client resource for home blood glucose monitoring, including a video demonstration.

Figure 2. A portable blood glucose meter and a drop of blood from an ear vein can be used to measure cats' blood glucose concentrations at home.

Home blood glucose curves offer substantial benefits for veterinarians, patients, and owners. Evaluation of cats monitored with home blood glucose curves has shown that owners appreciate home blood glucose curves because they avoid the stress of hospitalization for their cats.10 In addition, cats are re-examined just as often, and owners aren't prone to changing insulin doses without consultation. In almost 40% of cases, home-based blood glucose curves suggested a different treatment plan than blood glucose curves performed at the hospital.11

Chronic renal insufficiency

Chronic renal insufficiency occurs in three times as many geriatric cats as geriatric dogs. Stabilized cats can live for many years with chronic renal insufficiency, so develop a comprehensive management plan for these patients. Your goal is to help cats enjoy longer, higher-quality lives by lessening clinical signs and systemic complications and preventing further renal function deterioration. Chronic renal insufficiency complications in cats include renal secondary hyperparathyroidism, hypertension, hypokalemia, proteinuria, anorexia, and anemia.

Cats and owners benefit when you teach owners to administer subcutaneous fluids at home. Administering about 100 ml of crystalloid fluids daily subjectively appears to improve quality of life. Offering water flavored with low-sodium chicken broth or clam juice and using recirculating water fountains may also increase cats' water intake.

Don't restrict dietary protein for cats experiencing mild to moderate chronic renal insufficiency (creatinine 1.6 to 2.8 mg/dl, 140 to 250 μmol/l) because it can lead to protein malnutrition. These cats require adequate protein and calories to maintain body weight and to avoid muscle wasting and anemia. Protein restriction decreases hemoglobin production, promoting anemia, and decreases plasma protein levels, causing muscle wasting. Cats with moderate to severe chronic renal insufficiency (creatinine >2.9 mg/dl, 251 μmol/l), however, will benefit from dietary protein and phosphorus restriction to avoid uremia complications. The signs of uremia in cats include lethargy, depression, anorexia, and vomiting due to gastritis. Choose a palatable diet, preferably canned, with protein of high biological value.

Never try to force an anorexic patient with chronic renal insufficiency to eat a protein-restricted diet. Instead, concentrate on encouraging anorexic patients to eat. Controlling uremic gastritis with H2 receptor blockers such as famotidine (0.5 mg/kg orally every 24 to 48 hours) or ranitidine (2 mg/kg orally every 12 hours) may help inappetent cats eat more.

Nauseated cats may benefit from metoclopramide (0.2 to 0.4 mg/kg orally every eight hours) given 30 minutes before feeding. Use cyproheptadine (1 to 2 mg/cat orally) as needed to stimulate the cat's appetite. About 20% to 30% of patients with chronic renal insufficiency are hypokalemic at presentation (Figure 3), so monitor serum potassium and supplement with potassium gluconate (2 to 4 mEq orally every 12 hours) as necessary. Correcting hypokalemia improves the patient's well-being and appetite.

Figure 3. Cervical ventroflexion is a common clinical sign in cats with severe hypokalemia, often associated with chronic renal insufficiency.

Renal secondary hyperparathyroidism occurs in 80% or more of patients with chronic renal insufficiency. To maintain normal serum phosphorus concentrations, use intestinal phosphate binders such as aluminum hydroxide (90 to 100 mg/kg/day orally, divided doses with food, increase as needed). A new phosphate binder that may be useful for cats that do not tolerate aluminum hydroxide is sevelamer hydrochloride (Renagel—Genzyme Corp.; suggested dose 200 mg orally every eight to 12 hours with food), although it requires further investigation to define its benefits and a definitive dose for cats.

Calcitriol (2 to 3 ng/kg orally every 24 hours) may help prevent and treat elevations in parathyroid hormone (PTH) concentrations associated with chronic renal insufficiency. Controlling PTH may reduce PTH toxicosis, slowing chronic renal insufficiency progression and improving appetite and well-being. It is only administered when phosphorus concentrations are normal and the calcium × phosphorus product is under 60. It's important to educate clients and ensure compliance when you use calcitriol because you must monitor patients' PTH and ionized calcium concentrations regularly. Serum calcium must be monitored at one and two weeks after the start of calcitriol therapy and every six months thereafter. PTH levels should be monitored monthly until normalized.

Angiotensin-converting enzyme (ACE) inhibitors are receiving much attention for their role in managing cats with chronic renal insufficiency. Benazepril (0.5 to 1.0 mg/kg orally every 24 hours) improves survival time, quality of life, appetite, and weight gain in proteinuric patients with chronic renal insufficiency.13 Consider benazepril for patients with a urine protein-creatinine ratio of more than 0.4.

Anemia occurs in some patients with chronic renal insufficiency for a variety of reasons, including reduced erythropoietin secretion, blood loss from uremic gastritis, and inadequate dietary protein that leads to reduced hemoglobin production. Consider treating patients with recombinant human erythropoietin when a nonregenerative anemia (packed cell volume [PCV] <20%) is present. Administer 75 to 100 U/kg of erythropoietin subcutaneously three times a week until the PCV returns to low normal (24% to 30%). Then reduce the dose and frequency to 50 to 75 U/kg subcutaneously two times a week. Monitor the PCV and blood pressure carefully, especially in the first 60 to 90 days of treatment, because anti-erythropoietin antibodies can form in up to 20% of treated cats, leading to severe anemia. If the PCV declines severely during treatment, stop administering the drug and, if necessary, provide blood transfusions until the patient's PCV recovers and stabilizes.

Hyperthyroidism and chronic renal insufficiency

Hyperthyroidism and chronic renal insufficiency are common diseases of senior

cats and often occur concurrently. Diagnosis can be difficult because the clinical signs of the two illnesses can overlap. About 50% of cats with both hyperthyroidism and chronic renal insufficiency will have a normal total T4 concentration on a single measurement.13 If a cat with chronic renal insufficiency has a palpable thyroid nodule and a normal T4 concentration, pursue a diagnosis of hyperthyroidism using thyroid scintigraphy or T3-suppression testing.

Hyperthyroidism causes increased glomerular filtration rate and renal blood flow, which may mask underlying chronic renal insufficiency. Many cats with both diseases will be azotemic at the time of diagnosis. However, azotemia develops following hyperthyroidism treatment in about 15% to 23% of cats.13 When you treat hyperthyroidism, renal blood flow and glomerular filtration rates decrease, revealing chronic renal insufficiency in cats that had marginal renal function before therapy.

Managing cats with concurrent hyperthyroidism and chronic renal insufficiency presents special challenges. If a cat has hyperthyroidism and azotemia or you suspect chronic renal insufficiency, perform a methimazole challenge test. This allows a reversible way to treat the hyperthyroidism while evaluating renal function. Start methimazole treatment at 2.5 mg/cat every 12 hours and re-evaluate a serum chemistry profile for renal function and T4 levels after two weeks if you administer the drug orally and after four weeks if you administer the drug transdermally. If renal function is stable, you may increase the methimazole dose to achieve euthyroidism.

If the cat retains stable renal function once euthyroidism is achieved with methimazole, you may institute long-term therapy or pursue radioiodine treatment or thyroidectomy. If renal function deteriorates, you and the owner must make treatment choices. You may opt to continue treatment with methimazole to control hyperthyroidism and manage any clinical signs of chronic renal insufficiency that develop. These patients often fare best when you adjust their methimazole dosages to achieve a total T4 concentration in the upper end of the reference range. Or you may opt to treat the hyperthyroidism with atenolol (6.25 to 12.5 mg/cat orally every 24 hours) instead to reduce the cardiovascular effects of the disease and delay azotemia onset by avoiding the use of methimazole. With careful monitoring and management, these cats can have a good quality of life and be rewarding to treat.

Hypertension

Hypertension is the most important cardiovascular disease affecting geriatric cats because of its devastating impact on many body systems, including the eyes, kidneys, heart, and central nervous system. Many cases of feline hypertension are secondary to an underlying disease. For example, hypertension occurs in 29% or more of patients with chronic renal insufficiency, but 17% to 50% of cases may represent essential or primary hypertension.14

I recommend performing blood pressure screening for all geriatric cats as well as cats with such conditions as chronic renal insufficiency, hyperthyroidism, and heart disease.

Several devices using technologies such as oscillometry and Doppler ultrasonography measure systemic blood pressure. It takes patience to get accurate blood pressure readings in cats. Train your technicians to perform these time-consuming measurements. Use a quiet room, have the owner present, and allow five to 10 minutes for acclimation. Perform a minimum of five to seven measurements. It's important to use the correct cuff width (30% to 40% of the circumference of the leg) and place the cuff at heart level.14

Patients with systolic blood pressure elevations above 170 mm Hg recorded on more than one occasion should be treated for hypertension. It is important to identify and treat any underlying diseases first, such as hyperthyroidism. The most effective drug is the calcium channel blocker amlodipine (0.625 to 1.25 mg/cat orally every 12 to 24 hours).15 If improvement doesn't occur after 48 to 72 hours, increase the dose.15 If you reach the dose's upper range without controlling blood pressure adequately, add an ACE inhibitor such as benazepril (2.5 mg/cat orally every 24 hours for cats weighing 2.5 to 5 kg). In hyperthyroid cats, consider beta-blockers such as atenolol (6.25 to 12.5 mg/cat orally every 24 hours) as first-line therapy instead. Once stabilized, cats with hypertension should be re-evaluated at least every three to four months, or as dictated by any concurrent diseases. At each visit, measure systolic blood pressure in addition to performing a complete physical examination. Depending on the existence of concurrent diseases, serum chemistry profiles and other diagnostics may also be re-evaluated at least every six months.

Conclusion

Make sure all staff members help care for patients with chronic diseases. Everyone needs to deliver the same message of high-quality care. In addition to performing blood pressure measurements, technicians can also teach clients how to administer insulin, perform blood glucose readings, and give subcutaneous fluid therapy at home. A team approach will help you offer more efficient care and make staff members feel involved in delivering high-quality care.

Susan Little, DVM, DABVP, received her BSc from Dalhousie University, Nova Scotia, in 1983 and her DVM in 1988 from the Ontario Veterinary College, University of Guelph, Ontario. She co-owns two feline specialty practices in Ottawa, Ontario, and serves as vice president of the Winn Feline Foundation.

References

1. U.S. Pet Ownership and Demographics Sourcebook. Schaumberg, Ill: AVMA, 2002.

2. Zoran DL. The carnivore connection to nutrition in cats. J Am Vet Med Assoc 2002;221:1559-1567.

3. The path to high-quality care: Practical tips for improving compliance. Lakewood, Co: AAHA, 2003:61.

4. Center SA, Harte J, Watrous D, et al. The clinical and metabolic effects of rapid weight loss in obese pet cats and the influence of supplemental oral l-carnitine. J Vet Intern Med 2000;14:598-608.

5. Greco DS. Diet and feline diabetes mellitus: The carnivore connection, in Proceedings. Atlantic Coast Vet Conf 2002.

6. Bennett N, Greco DS, Peterson ME. Comparison of a high fiber vs low carbohydrate diet for the treatment of diabetes mellitus in cats (abst). J Vet Intern Med 2001;15:297.

7. Marshall RD, Rand JS. Comparison of the pharmacokinetics and pharmacodynamics of glargine, protamine zinc and porcine lente insulins in normal cats (abst). J Vet Intern Med 2002;16:358.

8. Rand J, Marshall R. Insulin glargine and the treatment of feline diabetes mellitus, in Proceedings. ACVIM Forum 2004.

9. Marshall RD, Rand JS. Insulin glargine and a high protein-low carbohydrate diet are associated with high remission rates in newly diagnosed diabetic cats (abst). J Vet Intern Med 2004;18:401.

10. Kley S, Casella M, Reusch CE. Evaluation of long-term home monitoring of blood glucose concentrations in cats with diabetes mellitus: 26 cases (1999-2002). J Am Vet Med Assoc 2004;225:261-266.

11. Gunn-Moore D. Influence of proteinuria on survival time in cats with chronic renal insufficiency (abst). J Vet Intern Med 2003;17:405.

12. Scherk M. Feline renal update: Where are we in 2005, in Proceedings. West Vet Conf 2005.

13. Chew DJ, Brown S. The hyperthyroid cat with renal failure, in Proceedings. West Vet Conf 2005.

14. Atkins CE. Feline hypertension: Risks and management, in Proceedings. West Vet Conf 2005.

15. Tilley LP. How-to's of hypertension management, in Proceedings. West Vet Conf 2004.