Dysplasia is defined generally as an abnormality of development in which the adult cells and tissues are abnormal in size, shape, organization and/or function. Renal means pertaining to the kidneys. Renal dysplasia, then, is defined as a developmental abnormality of one or both. It usually is characterized by small, misshapen kidneys at the time of birth that do not mature normally in terms of size, shape, organization and/or function. This is a congenital kidney disorder – one that is present at birth.
Causes of Renal Dysplasia
Renal dysplasia can be caused by several different things, although the exact causes are not well-understood. Some authorities suggest that renal dysplasia may be caused by bacterial or viral infection of fetal tissues as they develop inside the mother's uterus (this is called intrauterine fetal infection). Canine herpesvirus has been reported as one potential cause of intrauterine fetal viral infections. Another possible cause is the mother's ingestion of or exposure to toxins, or physical trauma to the fetus, during the course of the pregnancy.
In addition, there are a number of hereditary defects in kidney development that have been seen in domestic dogs. These tend to occur more commonly in certain breeds. Some dogs inherit renal dysplasia as a result of what is referred to as an autosomal recessive gene. This means that affected dogs can be of either gender, and that both parents are either carriers of the gene or are themselves affected with the disorder. In Samoyeds, renal dysplasia is reportedly caused by what is called an X-linked trait, which means that many more males than females develop clinical symptoms of the disease.
According to most experts, dogs known or suspected to have renal dysplasia should not be part of any responsible breeding program, given the strong genetic component associated with this disorder. Repeated breedings of the parents of affected puppies probably should be avoided, as well.
Puppies are not born with fully mature kidneys. In fact, significant development, maturation and microscopic cellular changes in the kidneys occur during the first two to three months of a dog's life. After that time, biopsies of kidney tissue should appear normal when examined under a microscope, through a process known as histology or histopathology.
How Renal Dysplasia Affects Dogs
Renal dysplasia is one of several congenital kidney disorders that can be seen in domestic dogs, which means that the disorder is present at birth. However, the actual symptoms of renal dysplasia may not become apparent for weeks to many months, despite the fact that the abnormality exists when the affected dog is born. Sometimes, symptoms of renal dysplasia never are noticed by the owners of affected dogs.
The signs of renal dysplasia depend upon the severity and types of kidney disorders that are present in the particular dog. Symptoms can include abnormalities in urine production, concentration or excretion. They also can include excretion of nutrients or substances in urine that normally should be retained in circulating blood.
Symptoms of Renal Dysplasia
Dogs whose kidneys have developed abnormally can manifest a number of symptoms, most of which usually are tied to chronic renal insufficiency or failure. They typically include one or more of the following:
Increased formation and excretion of a large volume of urine (polyuria; PU; usually evident by 6 to 24 months of age)
Increased thirst or excessive water intake (polydypsia; PD; usually evident by 6 to 24 months of age)
Blood in the urine (hematuria)
Failure to have normal heat cycles (anestrus)
Lack of appetite (inappetence; anorexia)
Poor growth (stunted growth)
Poor weight gain (body wasting)
Poor wound healing
Pale mucous membranes (pallor)
Poor hair coat
Poor body condition
Oral sores (oral ulceration)
Bad breath (halitosis)
Dogs at Increased Risk
Renal dysplasia has been reported in more than 20 breeds of companion dogs, including the Alaskan Malamute, Bedlington Terrier, Chow Chow, Cocker Spaniel, Doberman Pinscher, Golden Retriever, Keeshond, Lhasa Apso, Miniature Schnauzer, Norwegian Elkhound, Samoyed, Shih Tzu, Soft Coated Wheaten Terrier and Standard Poodle. It appears that certain family lines of dogs are more commonly affected. Dogs with unilateral renal dysplasia (where only one kidney is developmentally abnormal) may or may not ever show signs of kidney disease or failure, depending upon the functional health of the other kidney.
How Renal Dysplasia is Diagnosed
Dogs born with abnormal kidneys can develop a number of nonspecific clinical signs. Alternatively, they may never show symptoms at all. It is not particularly difficult for veterinarians to detect renal abnormalities. However, it is important to pinpoint the reason for the renal dysfunction, so that appropriate treatment or management protocols can be established.
When a veterinarian sees a dog that just "ain't doing right" (called "ADR" in veterinary circles), he will give that dog a thorough physical examination and will take a complete history from the owner of the dog's health, diet, living conditions, immunization status and other pertinent subjects. The dog may be lethargic, tired and skinny and may be drinking much more water – and "peeing" much more urine – than it normally does. The attending veterinarian will probably recommend an initial database that includes drawing blood samples for a complete blood count (CBC) and serum biochemistry profile. These routine tests are very valuable to assess a dog's overall systemic health. The veterinarian also likely will suggest taking a urine sample for assessment of kidney function. The urine sample may be submitted for culture and sensitivity, to determine whether a bacterial urinary tract infection is present and, if it is, which antibiotics would be best to treat the condition. Most dogs with renal dysplasia will have abnormal results on these tests.
Abdominal radiographs (X-rays of the abdomen, or "belly") may be taken. In affected dogs, they may reflect small, underdeveloped kidneys and possibly other renal abnormalities. Ultrasound of the abdomen is also useful to identify irregularly small kidneys and abnormal kidney structures and tissues.
Ultimately, the only way to confirm and definitively diagnose renal dysplasia is to take tissue biopsies from both of the dog's kidneys and submit them to a veterinary pathology laboratory. The laboratory will assess the biopsy samples through a process called histopathology. Histopathology (also called histology) is an area of anatomy that deals with the microscopic structure, composition and function of tissues and organs. Highly trained veterinary pathologists can look at tissue samples under a microscope and determine whether they are normal or abnormal. Usually, if the samples are abnormal, skilled pathologists can determine and tell the treating veterinarian why that is so. Dogs over 2 to 3 months of age should have normal kidney tissue and structures when examined microscopically. If the biopsy samples show poorly developed, immature and/or disorganized kidney tissues that are inappropriate for the animal's age, renal dysplasia is the likely culprit.
Genetic tests are available to identify the genetic mutations that cause renal dysplasia in Lhasa Apsos, Shih Tzus and Soft Coated Wheaten Terriers. Over time, such tests probably will become available for many additional breeds.
Kidney abnormalities are not especially difficult to diagnose. Unfortunately, they can be quite difficult, if not impossible, to successfully treat.
Dogs with renal dysplasia should have their blood chemistry and urine content monitored periodically to determine whether their kidney function is changing for the better or the worse over time. They should be fed a low sodium diet to prevent excess water retention. Many authorities recommend feeding dogs with kidney damage a diet that is low in protein and comprised only of high-quality protein sources, because protein is usually poorly metabolized by dogs with compromised kidney function. Most veterinarians and nutritional experts agree that phosphorus intake should be restricted in dogs with kidney disease. Dietary modification can be used to reduce phosphorus intake. Medications are also available and may be necessary, together with dietary adjustments, to lower and maintain circulating phosphorus at appropriate levels. Several different prescription diets are available through veterinarians that are specifically formulated to help manage and relieve some of the symptoms of kidney dysfunction. The appropriate "kidney diet" should be tailored to the individual patient.
Free access to fresh, clean water should be provided to dogs with kidney abnormalities at all times, unless otherwise recommended by the treating veterinarian. Dogs with symptomatic renal dysplasia will produce and excrete abnormally large amounts of urine and will need to drink enough water to compensate for their excessive urine output to avoid dehydration. In some cases, intravenous (IV) or subcutaneous (sub-Q) fluids may need to be administered. IV fluids must be given in the veterinary clinic. However, most owners can easily learn how to administer sub-Q fluids at home. This can be very important to a dog's comfort, especially during the end-stages of renal failure. If a dog is dehydrated due to vomiting and/or diarrhea, certain medications – called anti-emetics and anti-diarrheics - can be prescribed to reduce vomiting and firm up the dog's stool.
Other management options that may be recommended by veterinarians for dogs with renal dysplasia include supplementing their diets with vitamin B and/or sodium bicarbonate. Many dogs with kidney disease excrete B vitamins in their urine and can be helped by vitamin B supplementation. Sodium bicarbonate may be recommended by the veterinarian if the dog has what is known as an acid-base imbalance. Acid-base regulation involves the body's maintenance of appropriate pH levels in circulating blood. The kidneys and the respiratory tract are involved in maintaining normal acid-base ratios. This is an extremely complex, but also an extremely important, process.
Dogs with renal dysplasia that become severely dehydrated can decompensate very suddenly and go into what is called a uremic crisis. These animals need to be hospitalized immediately and rehydrated with intravenous fluids and balanced electrolyte solutions, to restore hydration and correct acid-base imbalances.
Dogs with severe bone pain associated with kidney dysfunction can be given prescription anti-pain medications called analgesics. Analgesics can be administered orally, subcutaneously or intravenously and can range from very mild pain relievers to stroing opioid drugs. Administration of oral calcitriol or other supplements may delay or help prevent the bone changes that can result from kidney disorders. The appropriate balance of blood calcium and phosphorus levels can be very tricky to maintain in dogs with renal dysfunction.
Kidney dialysis, and kidney transplantation, may be available for dogs with severe renal dysplasia, although these procedures are only offered at highly specialized referral centers and at some veterinary teaching hospitals. They are quite costly. These potential treatment options should be discussed with the dog's attending veterinarian to determine whether they are realistic options.
The prognosis for dogs with renal dysplasia depends upon the degree of their kidney dysfunction, their age at the time of onset of symptoms, the severity of their functional abnormalities at the time of diagnosis and the effectiveness of medical management. Underdeveloped and dysfunctional kidneys almost always result in renal failure and, eventually, death. In most cases, the long-term outlook for survival is poor. However, if only one kidney is affected (unilateral renal dysplasia), and if the other kidney functions normally, affected dogs may live a normal, full life. Most dogs do very well with just one healthy kidney. Unfortunately, unilateral renal dysplasia is the exception, not the rule.