Chronic kidney disease, one of the most common diseases among dogs and cats, involves the loss of functional renal tissue due to a prolonged, usually progressive process. But thanks to both traditional and cutting-edge methods for diagnosing and treating the condition, veterinarians have more options than ever for helping these animals enjoy longer lives.
Causes, Signs and Symptoms
In most cases of chronic kidney disease, the underlying cause is unknown, says Mark Acierno, DVM, Dipl. ACVIM, MBA, an associate professor and dialysis service coordinator at Louisiana State University’s School of Veterinary Medicine in Baton Rouge.
“It’s likely a combination of environmental and congenital factors, but we’re really not sure in most cases,” Dr. Acierno says. “Sometimes there’s a defining event, but often there isn’t.”
The causes can be categorized in different ways, adds Anthony Ishak, DVM, Dipl. ACVIM, of BluePearl Veterinary Partners in Tampa, Fla.
“There are acute insults that destroy enough renal parenchyma in an irreversible manner and result in decreased functional renal mass,” Dr. Ishak says, citing leptospirosis, pyelonephritis, lilly intoxication, ethylene glycol intoxication, hypovolemia/hypotension, pancreatitis and sepsis as examples. “There are also chronic diseases that result in progressive loss in renal function over time, such as interstitial nephritis, chronic partial ureteral obstructions and polycystic kidney disease.”
Chronic kidney disease looks different in cats and dogs, Acierno says. Cats can live with the disease for years and “do really well with it,” he says. In geriatric patients at referral institutions, chronic kidney disease affects up to 35 percent of cats, though the prevalence in the general population is likely lower. Dogs are another matter.
“It’s been estimated that chronic kidney disease will strike 10 percent of dogs over the age of 12,” Acierno says. “But they don’t do as well with it. Chronic kidney disease in dogs doesn’t seem to go for years and years as it does in cats.”
In general, however, chronic kidney disease tends to affect older animals, and it often smolders for months or years before it becomes clinically apparent. Dogs and cats come into the office looking “underweight, emaciated, anorectic, dehydrated and maybe vomiting,” Acierno says, noting that the vomiting is often one of the primary reasons owners bring in their pets. “A lot of these animals are also hypertensive.”
Dogs and cats affected by chronic kidney disease show other signs, too, Ishak says.
“Occasionally, more specific signs such as renal pain, pigmenturia, uremic stomatitis and anemia are present depending on disease severity and underlying etiology,” he says.
Clinical Findings and Diagnosis
Renal disease is typically diagnosed when azotemia becomes apparent on screening chemistry panels as animals age, Ishak says.
“Sometimes abnormalities are detected when routine urinalysis is done,” he says. “Earlier changes can be found with imaging such as radiographs or ultrasound and careful attention to blood pressure and urinalysis results, especially the presence of proteinuria, over time. A glomerular filtration rate is an ideal method of assessing decline in renal function over time.”
Usually, the earliest clinical signs commonly attributable to renal dysfunction are polydipsia and polyuria, which are not observed until the function of about two-thirds of the nephrons have been impaired.
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As the disease progresses, anorexia, weight loss, dehydration, oral ulceration, vomiting and diarrhea fully manifest. In imaging studies and through physical examination, the animal’s kidneys also may appear abnormal, Acierno says.
“Classically, there is a non-concentrated urine,” he says. “Sometimes it may have protein in it, sometimes it may not. And in looking at the kidneys themselves, they tend to be small and irregular. Sometimes you can palpate that, but certainly with ultrasound and sometimes even X-ray, you can interrogate the kidneys and see that they’re not normal.”
A combination of survey radiography, abdominal ultrasound, clinical pathology tests and blood pressure measurements will allow practitioners to evaluate the severity of the disease and establish a prognosis, Acierno says.
“Blood test, urinalysis and some sort of diagnostic imaging, such as an ultrasound, is the way to go,” he says.
With appropriate therapy, animals can survive for long periods with only a small fraction of functional renal tissue, perhaps 5 to 8 percent in dogs and cats. The key is managing it, says Acierno, and one way to do that is through diet.
Chronic kidney disease patients tend to be azotenic, acidotic, hyperphosphatemic, hypertensive, anemic and dehydrated. “That’s a lot of things to worry about,” Acierno says. “But we can control the azotemia, acidosis and elevated phosphate levels very often by just changing to an appropriately formulated renal failure diet. They tend to be low-protein, low-phosphate and bicarbonate balanced so they don’t promote acidosis.”
High phosphate levels that aren’t affected by diet can be managed with phosphate binders, such as aluminum hydroxide and other proprietary drugs, he says.
To manage the hypertension, which is a greater than 150 mm of mercury systolic blood pressure, practitioners should treat with calcium channel blockers and ACE inhibitors, Acierno says.
“In dogs, we usually start with an ACE inhibitor and then add a calcium channel blocker if we don’t get the appropriate response,” he says. “In cats, for physiologic reasons, we often do just the opposite.”
Careful blood pressure monitoring is critical, Acierno says.
“Hypertension can be caused by renal failure, and hypertension can cause renal failure,” he says. “So if you don’t get the blood pressure under control, you can find your patient spiraling downward very quickly.”
Anemia can be managed with recombinant erythropoietin and the human drug epogen, but animals can develop antibody response to the proteins. A newer—and more expensive—alternative is a synthetic form of erythropoietin called darbepoetin alfa.
“In it, the molecules are camouflaged with carbohydrate molecules,” Acierno says. “So when the body’s immune system sees it, it lets it go right by.”
And to manage the animals’ dehydration, Acierno recommends that owners give their pets at-home subcutaneous fluids.
“We’ll send our patients home with a bag of fluids, some needles and a drip line,” he says. “Basically, we stick a needle under the skin and create a fluid pocket that gets reabsorbed over a period of time to keep the animal hydrated.”
Other options include a wet diet, subcutaneous catheter or an esophagostomy tube, Acierno says.
Caring for dogs and cats with chronic kidney disease requires careful monitoring and owner education—and a skilled in-clinic team, Acierno says.
“Getting a blood pressure, client education and things like that are all billable events,” he says. “Some of our technicians are extremely well-skilled at getting blood pressures and educating clients about subcutaneous fluids, and we use those tools to our advantage.”
This Education Series story was underwritten by Vétoquinol USA of Fort Worth, Texas.