The kidneys are the body’s filtering mechanism. Microscopic funnel-shaped tubes called nephrons are responsible for purifying the blood and preventing the build-up of toxins and other wastes. Nephrons are susceptible to damage from many causes including infection, trauma, cancer, auto-immune diseases, poisons, aging, and genetic predisposition. Because the kidney has a large reserve capacity and healthy nephrons have the ability to increase their filtering functions, the kidney can compensate for such damage. If the change occurs gradually as with damage due to aging, the kidneys can continue to function with as little as 25 percent of the original nephrons. When the number of functioning nephrons drops below this level, kidney failure occurs; there are no available treatments to promote the regrowth of kidney tissue.
After the kidneys have completed the filtering process, urine passes from them through the ureters and into the bladder where it is stored. When the bladder is full, urine is excreted through the urethra.
Acute Kidney Failure
Acute kidney failure refers to a sudden loss of kidney function due to poisoning, trauma, infection, or heatstroke. The most common culprits are ethylene glycol (a component of antifreeze), rat poison, Leptospirosis (a bacterial illness contracted through exposure to contaminated water or food), and, ironically, some antibiotics. If caught early enough, the dog’s kidney function can often be maintained through aggressive supportive treatment, and the prognosis for full recovery is good.
Chronic Kidney Failure
Chronic kidney failure is the most common form of kidney disease in dogs and is also among the most common causes of death in dogs, especially older ones. Unfortunately, it is a silent killer. It progresses slowly over a period of years and often goes unnoticed, even by the most vigilant of owners. It is considered incurable. However, the progression of the disease depends on the underlying cause and with careful management the dog can often live comfortably for years after the initial diagnosis.
Detection
Frequently, the dog remains symptom free until he is in the latter stages of kidney failure. Weight loss, listlessness, poor appetite, and nausea coupled with excessive water consumption and urination are the most common signs of advanced kidney disease.
However, early detection of occult renal disease is critically important to the long-term prognosis. It is suggested that a baseline blood work-up and urinalysis be done annually, beginning at three years of age, although it certainly can be done earlier. Unfortunately, many of the real sign-posts of kidney disease are not apparent until kidney function is already severely impaired. It is vitally important to raise the index of suspicion: age, chronic inflammation or infection (such as periodontal disease, recurring urinary tract infections, etc.), changes in the skin, and that all important intuition warrant further investigation into the dog’s kidney function.
If any of the above symptoms are apparent in the dog, blood work and a urinalysis should be done immediately. The critical readings will be the BUN (blood urea nitrogen), creatinine, phosphorus, and potassium levels, as well as the specific gravity of the urine. Further, more comprehensive tests may be warranted, including ultrasound, to determine the extent of the damage and to determine, if possible, the underlying cause of the kidney disease.
Treatment
While it is not possible to cure chronic kidney disease, it is certainly possible to prolong the pet’s life, while also maintaining the quality of that life. Again, early detection is critical.
In an acute stage of chronic kidney failure, hospitalization is often required. Intense IV fluid therapy is instituted to flush the built-up toxins from the system. When the patient is sufficiently stabilized, subcutaneous fluid administration at home is often an option. Dialysis and kidney transplants are also available options, but they are not usually practical ones, and canine organ transplants have produced few long-term survivors.
Diet is an extremely important consideration, and may be the most viable route to maintaining the kidney patient at home. For years, the recommendation was to immediately reduce the level of protein in the dog’s diet; it was even suggested that all older dogs receive a reduced protein diet, even those showing absolutely no symptoms of kidney impairment. Current thinking is that treatment must be individualized, and while diets extremely high in protein should be avoided, perhaps the quality of the protein fed is of paramount importance. If phosphorus levels are elevated, it is vital to restrict dietary phosphorus. Levels of sodium and other minerals in the diet should also be carefully monitored. There are a number of commercial kidney diets available, but the ingredients are often not the highest quality (despite well-known brand names), and studies have shown that moderate amounts of easily digestible, very high quality protein sources are the best choices for the kidney patient. Research these diets and the quality of their ingredients carefully or prepare the food at home. The process is not particularly burdensome, and if it prolongs the dog’s life it is certainly well worth the extra effort. If a home-prepared diet is chosen, consult with a veterinary nutritionist to ensure that the patient’s nutritional needs are met.
Supplementation with B-complex and vitamin C is often recommended to replenish vitamins lost due to excessive urination. Omega 3 and Omega 6 fatty acids may help to reduce kidney inflammation. Medications are available to help reduce the stomach irritation that often accompanies kidney disease, and there are drugs that help regulate phosphorus levels and possibly slow the progression of the disease. BE SURE TO CONSULT WITH YOUR VETERINARIAN BEFORE ADMINISTERING ANY MEDICATIONS OR SUPPLEMENTS.
With careful management and early detection, the kidney patient can in many instances live a long and comfortable life.
Types of Canine Renal Disease
Cystinuria
Cystinuria is an inherited disease characterized by an inability to reabsorb the amino acid cystine in the kidney tubules, resulting in an excess of cystine in the urine. Cystine is insoluble in neutral or acidic urine, so the formation of cystine crystals or, possibly, cystine uroliths (stones or calculi) in the kidneys, bladder, or urethra can result.
Because of the physiology of the male, irritation and blockage by calculi is much more common than in the female. Afflicted animals may present with recurrent urinary tract inflammations; they may experience difficulty in urination or pass blood-tinged urine. Males may become completely blocked and can face kidney failure, bladder rupture and death, while cystinuric bitches may remain asymptomatic.
Use of a specific urinary screening method, the nitroprusside spot test, will give a reliable diagnosis; examination of the urine for cystine crystals is not a reliable indicator since these crystals are not always present in the urine. Surgical removal of stones may be indicated. Special diets and medications may be helpful, but their efficacy has not yet been documented. There are two common drugs of choice that bind cystine and prevent crystal formation and, in some cases, they have been found to dissolve small stones, but not all dogs respond well to this treatment.
In Newfoundlands, cystinuria is inherited as an autosomal recessive trait. In simple terms, this means that affected dogs of both sexes have two mutant (diseased) genes. Their parents are either carriers (asymptomatic but carrying both a normal and a mutant gene) or are also affected (with two mutant genes). Due to the efforts of Newfoundland fanciers and Dr. Paula Henthorn at the University of Pennsylvania School of Veterinary Medicine, there is now a DNA test available which can determine the genetic status of individual Newfoundlands before breeding.
The disease has also been identified in Mastiffs and Bullmastiffs, though there is not yet confirmation of the autosomal recessives mode of inheritance in these breeds. At present, there exists no specific screening process for Bullmastiffs.
Glomerulonephritis
This is a disease characterized by the accumulation of antibodies along the walls of the glomeruli, small blood vessels that are an essential part of the filtering apparatus of the kidneys. Production of these antibodies can be brought on by an infectious process (i.e., brucellosis, tick-borne illnesses such as Lyme disease, etc.), an inflammatory process (such as prostatitis or pancreatitis), or by an allergic reaction. It can be classified as a protein-losing nephropathy. While there is a well-established link between infectious and inflammatory diseases and glomerulonephritis, the connection between allergies (specifically, food allergies) and this disease is presently being studied at the College of Veterinary Medicine at North Carolina State University with the support of The Morris Animal Foundation.
Often, there are no clinical signs until the disease is fairly advanced; proteinuria (the presence of excessive protein in the urine) is the primary indicator, perhaps coupled with weight loss and overall poor body condition. Once again, the importance of routine urinalysis and blood work in the detection of kidney disease cannot be stressed enough, although definitive diagnosis of this particular disease requires a renal biopsy.
There are treatments available but as with most kidney-related issues, the prognosis is generally poor.
As is often the case, when an underlying disease process cannot be identified, glomerular disease may be considered idiopathic. Spontaneous glomerulonephritis seems to occur more often in Labs and Goldens, but so far a genetic link has not been established.
Renal Amyloidosis
Amyloidosis refers to the accumulation of an abnormal protein in the tissues, resulting in organ failure and eventual death. Such proteins are implicated in a number of diseases, including Alzheimer’s, rheumatoid arthritis, diabetes, and cardiac irregularities. There have been cases in our breed where these proteins have settled in the kidneys, resulting in acute kidney failure and death. This disease can be classified as a form of protein-losing nephropathy.
It would appear from various studies that amyloid deposits accumulate, primarily in the kidneys, in the absence of an apparent underlying disease process. In most such instances, while the deposits appear confined largely to the kidney, minute deposits are also present in other tissues and organs tested. While it was previously assumed that the disease was a kidney-limited one, current thinking is that it is truly a generalized amyloidosis, but not one that is not necessarily caused by infection or inflammation as was once thought to be the case.
It appears to be an idiopathic disease, striking randomly and without warning. An underlying disease is detected in only about 50% of dogs with renal amyloidosis. For a dog diagnosed with this disease, the prognosis is poor. It is particularly resistant to medical treatment, and kidney failure is the inevitable outcome. As in other forms of kidney disease, the most common symptoms are decreased appetite, increased thirst and urination, weakness, vomiting, weight loss and lethargy.
Is there a genetic component at work here? To date, studies have identified an inherited form of renal amyloidosis in several breeds of cats and also in Chinese Shar-peis. Among older dogs,Beagles and Collies appear to be at higher risk than other breeds. So far, there have been no studies that point to an inherited predisposition to this disease in the Bullmastiff. An inherited form of protein-losing nephropathy has been identified in Soft Coated Wheaten Terriers and studies are underway at North Carolina State University to determine the mode of inheritance.
Juvenile Renal Disease
Also known as renal dysplasia or congenital renal hyperplasia, this is a congenital renal disease in which the kidneys themselves fail to develop properly. As with most kidney-related diseases, the symptoms include frequent drinking, frequent urination, dilute urine, and, since it occurs in youngsters, difficulty with house training. With the progression of the disease come other symptoms including vomiting, weight loss, anorexia, and bad breath. The disease can be noticed in pups as young as a few weeks old, and is almost always diagnosed before the age of two. Elevated BUN and creatinine levels coupled with protein in the urine are early indicators, but confirmation of the disease is best accomplished through a biopsy. In the early stages, dietary management and fluid therapy can help the patient maintain quality of life, but the prognosis is poor.
This disease is most commonly associated with Standard Poodles, but appears with some frequency as many as thirty breeds. While it is not common in Bullmastiffs, it has been diagnosed. Studies are presently underway to determine the exact mode of inheritance in those breeds where the disease is a particular problem.
Urinary Problems
Incontinence
Incontinence can affect any dog at any time, but is most prevalent in middle-aged spayed females and older neutered males. It can be a consequence of old age due to the weakening of the urethral sphincter muscle, senility, and/or decreased hormonal production. Incontinence is characterized by the leaking of urine, generally when the dog sleeping or resting, in a dog that is otherwise able to urinate normally. It is not to be confused with submissive urination that occurs when a dog is behaving in a submissive manner during times of excitement or fear.
Dogs with incontinence problems have a much higher incidence of bladder infections and they should be carefully monitored. They can also suffer from severe skin irritation as a result of urine leakage. These scalded areas can be treated with antibiotic salves.
Hormone responsive incontinence is generally diagnosed after other causes (such as infection or blockage) are ruled out. Treatment with synthetic estrogen for females and testosterone replacement for males can be quite effective.
Urinary Tract Infections
Dogs suffering from urinary incontinence are at a higher risk for bladder infections, but unaffected dogs may also contract bacterial infections.
Lower urinary tract infections affect the bladder and urethra. Symptoms include urgency, straining, frequency, hematuria (blood in the urine), and occasionally temporary incontinence. Blood tests will confirm the presence of bacteria, culture and sensitivity tests will help to determine which antibiotic will be most effective. These infections typically respond well to treatment.
Infections can also be present in the kidneys, and stones can form in both the kidneys and the bladder. These conditions will often result in hematuria, but straining and urgency are rarely present. Struvite crystals or stones are the form most often associated with infectious processes, while other types of stones are typically metabolic in origin. Diagnosis is generally confirmed through x-ray. Medication and dietary management can be helpful, but surgery may be indicated as well.
References
- www.geocities.com/Vienna/Opera/2167/
- www.cah.com/library/caninekidney.html
- www.antechdiagnostics.com/newsletters/9-00.html
- www.redveterinaria.com/cyber/nefrouro1.html
- www.vetprof.com/clientinfo/newf-cystinuria.html
- www.mastiff.org/exhibit-hall/health/cystart.mv
- www.vetmed.wsu.edu/boeing/small_animal_medicine/crf.htm
- www.peteducation.com/dogs.htm
- www.vetcentric.com
- www.bsava.com/members/publications/cdroms/renal.htm
- www.vetprof.com/clientinfo/juvenilerenal.html
