Juvenile Renal Dysplasia in Shih Tzu

JRD is a developmental or genetic defect of the kidneys. This makes it quite different from common forms of kidney disease which occur in adult or aged dogs and from other diseases and/or drugs which may cause inflammation of the kidneys and abnormal results on blood and urine tests of kidney function. It is found most commonly in Shih Tzu, Lhasa Apsos, and Soft-Coated Wheaten Terriers and is believed to be present, with less frequency, in several other breeds.

The disease usually progresses in three stages, each of which may have a variable and independent time course. STAGE ONE is the silent destruction and loss of nephrons over a period of months and years in the absence of symptoms.

STAGE TWO occurs when approximately 30% of functioning nephrons remain and clinical symptoms (excessive thirst and volume of urine, weight loss, lack of vigor, and intermittent loss of appetite) are first obvious. This stage may persist for months or years. In the FINAL STAGE, vomiting, weakness, dehydration, and severe debilitation are added to second stage symptoms, and death from renal failure (uremia) is the eventual outcome. End stage presents a real diagnostic problem because dogs in this stage have such severe histologic change that the presence of JRD can be obscured.

The dog is born with relatively immature kidneys. This changes rapidly in the first six weeks of life. In many animals, immature nephrons (urine-forming units) exist until 6-10 weeks of age. But in this disease, these immature nephrons persist throughout life. Also, some nephron units do not develop and are replaced with fibrous tissue. Sometimes this fibrous tissue represents 20-50% of the kidney. Other evidence of JRD includes diffuse interstitial fibrosis in the cortex and medulla (which seems quite peculiar to this disease), reduced numbers of glomeruli (the filtering structure of the kidney where toxins, fluid, and electrolytes are removed from the blood), dilated and hypoplastic tubules (through which the fluid or filtrate passes while being transformed into final urine), and a variety of sizes of glomeruli. Some glomeruli are 20-30% smaller than normal, some are normal size, and some are embryonic. While mineralization of tubules can be seen in any chronic renal disease, this mineralization is seen with JRD even in young animals that have only moderate uremia.

One may become suspicious of renal dysplasia in puppies older than eight weeks if excessive thirst, excessive volumes of urine, and pale urine are noticeable. Normal Shih Tzu puppies drink approximately one ounce of water per pound of body weight daily when eight to ten weeks of age, but dogs with severe renal dysplasia (over 35% hypoplastic glomeruli) may drink as much as five times that quantity. Therefore, a simple measurement of water intake per unit of body weight might be helpful. These figures are based on dogs that consume dry food; one cup of food with 1/3 cup of water.

Other symptoms occurring early in life in severely affected dogs include reduced body weight and stature compared to normal puppies. The reduced stature and body weight are due to metabolic disturbances of uremia which affect bone growth. Marked skeletal abnormalities such as bowed long bones and soft pliable bones of the jaw may be found. Severely affected dogs will fail to thrive at two or three months of age and progress to renal failure quickly. Not all puppies in a litter are uniformly affected. Moderately affected puppies (15-25% hypoplastic glomeruli) may appear normal until five or six months of age and then follow the same course, with chronic debilitation and death at nine to twelve months.

The classical symptoms of affected dogs just described would only be expected in severely and some moderately affected dogs. Many animals with the disease, however, are only slightly affected. They show no clinical signs, and the presence of the disease may fail to be detected by routine laboratory tests, including urinalysis, serum creatinine, BUN, radiographs of renal size, and ultrasound. Due to the nature of this disease, it can go undetected for many generations or be ignored by knowledgeable breeders because only a small percentage of animals will die of renal failure. A considerable amount of preliminary research attempting to locate a causal genetic mutation and devise a genetic test for JRD has been funded by the American Shih Tzu Club Charitable Trust and the American Lhasa Apso Club; additional research has since been funded by several other affected breeds.

The treatment of JRD is essentially the same as for any chronic renal failure disease. Recent studies suggest that a low protein diet may have little effect in preventing or delaying the development of JRD, but other conditions and some drugs may worsen it. Diet may not alter JRD’s progression, but phosphorus and protein-restricted diets help ameliorate symptoms in dogs with any form of kidney disease.

If your dog dies and you suspect that the cause of death is JRD, it is recommended that kidney tissue be sent for examination to the University of Pennsylvania School of Veterinary Medicine, Department of Pathology, 3800 Spruce St., Philadelphia, PA 19104 (Phone 215-898-8857), preferably with a pedigree to aid in future research on JRD. Your local veterinarian should call to discuss methods of collection and preservation of kidney specimens. The kidneys must be collected from the animal immediately after death and placed in 10% formalin solution; freezing destroys the tissue and precludes a diagnosis.

BUN and Creatinine, the two common blood tests of renal function, are not elevated until 70 to 75% of the kidney is nonfunctioning, and therefore are of little use in identifying mildly or moderately affected dogs. Having a BUN and creatinine in the normal range means that the dog has at least 30% kidney function. It does not mean that the dog is free of renal dysplasia. Elevated BUN and creatinine readings may also be caused by other renal problems, but these tests can be of some use in identifying severely affected dogs, particularly puppies already drinking and urinating excessively. Anesthetic should not be given to a dog with an elevated BUN, as such a dog is a surgical risk.

Most adult Shih Tzu with normal kidneys also have a urine specific gravity reading above 1.045. This is another test of kidney function; it does not tell you that your dog is free of renal dysplasia.

Most adult Shih Tzu with normal kidneys also have a urine specific gravity reading above 1.045. This is another test of kidney function; it does not tell you that your dog is free of renal dysplasia.

The E.R.D.-Screen Urine Test is a relatively new test for small amounts of protein (microalbuminuria) in the urine. It is not a kidney function test. If persistently positive, this test may indicate ongoing glomerular damage. While microalbuminuria may be caused by a number of diseases other than JRD, this test may detect the presence of renal dysplasia earlier than conventional blood and urine tests.

Ultrasound examination of the kidneys may be slightly more useful in identifying moderately affected dogs, whose kidneys may be smaller than normal size and show scarring. If X-rays of younger Shih Tzu show that both kidneys are markedly reduced in size, a presumptive diagnosis of dysplasia can be made. X-rays are less useful in older dogs with old-age kidney problems.

This disease has long presented a real dilemma for breeders. It may go undetected for many generations or be ignored by knowledgeable breeders because it is transmitted in a very silent fashion by many animals that either are or appear to be clinically normal.