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Review of Common Urologic Disorders
Julie Fischer, DVM, DACVIM, presented a lecture on common urologic conditions, including chronic kidney disease, acute ureteral obstruction, and incontinence.
The DC Academy of Veterinary Medicine hosts lectures throughout the year on topics of interest to practicing veter- inarians.
In April, Julie Fischer, DVM, DACVIM, presented a lecture on common urologic conditions, including chronic kidney disease (CKD), acute ureteral obstruction, and incontinence.
The session was hosted in Fairfax, Virginia, with remote sites in Maryland, Virginia, and Washington, DC. Dr. Fischer currently practices at the Veterinary Specialty Hospital of San Diego.
CKD is a challenging disease to treat due to its insidious nature and high risk for complications such as vomiting and an- orexia. Additionally, clients, general practitioners, and internists may all focus on differing aspects of the disease. For this reason, it is vital that all parties (clients, primary care veterinarians, and referral veterinarians) speak the same language when discussing the severity and prognosis of CKD.
Dr. Fischer reviewed International Renal Interest Society staging, as it may help guide therapeutic options. Nutritional management is key to sustaining patients with CKD, she noted; inappropriate nutrition may hasten progression of the disease.
Options for clients whose pets won’t eat the prescribed diet include force feeding, feeding an inappropriate diet, or placement of a feeding tube. Dr. Fischer was quick to discuss the many benefits of feeding tubes. In her experience, patients can live with a feeding tube for extended periods of time, thereby enhancing their quality of life through improved medication delivery and nutrition. “Food is medicine,” she said, “and feeding the appropriate diet for any disease state may help enhance outcomes.”
Feeding tube selection may be based on a number of factors. The intended duration of tube use is important, as some tubes (eg, nasogastric tubes) are intended for shorter-term use. Esophageal tubes can be in place for a week or more, with minimal expense, anesthesia, and recovery time. Percutaneous endoscopic gastrostomy (PEG) tubes are preferred for long-term (semi-permanent or permanent) use, but they should be used with caution in cases of vomiting. PEG tubes protrude from a gastric perforation and need proper care and covering to prevent infection. Jejunal tubes are less common but are recommended in cases of intractable vomiting.
Acute Ureteral Obstruction
Acute ureteral obstruction may result from inflammation, uroliths, neoplasia, trauma, mucus, or stricture. For ureteral obstruction to cause azotemia, both ureters must be impacted. This may occur in patients with bilateral disease or in those with unilateral disease without contralateral compensation.
The most common cause of ureteral obstruction is calcium oxalate urolithiasis, the incidence of which has increased over the past 20 years. In cases of unilateral obstruction, it may be possible to identify asymmetric kidneys on palpation or radiography. In acute obstruction, the patient may show signs of pain or behavior changes. In chronic obstruction, the affected kidney will be small, firm, and nonpainful while the functional kidney may be enlarged, turgid, and painful.
Acute ureteral obstruction increases ureteral pressure, resulting in an increase in proximal tubular pressure, which leads to an increase in renal blood flow and additional increases in ureteral pressure. Simultaneously, an increase in glomerular capillary pressure occurs, but the net hydrostatic pressure gradient across the glomerular capillaries decreases (due to the much higher ureteral pressure), resulting in a decreased glomerular filtration rate (GFR). Several hours later, intratubular pressures decrease, but glomerular capillary pressures decrease faster, so GFR remains significantly diminished. After 24 hours of obstruction, the contralateral kidney begins to compensate, and prostaglandins temporarily increase renal blood flow to the cortex, but GFR continues to diminish (~50% at 24 hours, ~30% at 6 days, ~20% at 2 weeks, ~12% at 8 weeks).
Interstitial fibrosis begins to develop following obstruction. Interstitial collagen increases are detectable by 7 days post obstruction. Fibrosis and tubular basement membrane thickening are detectable by 16 days post obstruction. The severity of the renal damage largely depends on the duration and severity of the obstruction. The longer the obstruction is present, the more severe the fibrosis and the less likely a kidney will be to recover. If treated promptly, urine concentrating ability can recover fully.
Clinically, these patients may present with a variety of signs. Many are painful, but some animals may be moribund while others are bright and alert. Careful assessment of hydration is vital, as many patients may be oligoanuric and overhydrate as a result. Dr. Fischer recommends assessing skin turgor because uremic toxins may create dry mucous membranes. Retinal hemorrhaging may also be present and cerebral damage may occur due to hypertension, resulting in “sudden blindness,” a decreased menace response, and/or decreased pupillary light reflex.
Imaging is important to assess the severity and stage of kidney disease. Radiography can be highly sensitive for the diagnosis of ureteroliths. Survey radiographs can also help identify kidney size and shape. Ultrasound, however, is good for evaluating renal pelvic dilation. If surgery is planned, computed tomography or contrast radiography is needed to assess the location of the obstruction.
Medical management of acute ureteral obstruction focuses on appropriate diuresis while managing signs of uremia. Selective a1 agonists, such as prazosin, can be used for ureteral relaxation; up to 20% of patients will have spontaneous clearance of the obstruction when treated with judicious fluids and ureteral relaxants. Amitriptyline relaxes urinary smooth muscle and may be considered as an adjunct therapy. Extracorporeal shock wave lithotripsy is often used in humans and may be considered if geographically and financially feasible.
In many acute cases, surgery is required to resolve the obstruction. These surgeries are technically difficult and may be expensive, and the patient is at high risk (~30%) for post-operative complications, such as urine leakage. Subcutaneous ureteral bypass ports and stenting are other options, as is surgical removal of the blockage via ureterotomy.
Incontinence is a common complaint in practice. Incontinence is usually due to failure of urine storage during filling, although in some patients (particularly animals with congenital disorders) multiple mechanisms may be at play. Causes of incontinence are traditionally described as neurogenic or non-neurogenic in nature. For a pet to be continent, it must have ureters that open solely into the bladder, bladder capacity and sphincter tone, and nervous system communication to maintain the system. Urinary incontinence is defined as involuntary leakage of urine through the urethra. Incontinence is most common in female dogs but is also seen in male dogs and in cats. In neurogenic incontinence, nervous system communication fails but the urinary organs function normally. These cases often involve the sacral spinal cord and/or the pudendal nerve, resulting in a loss of normal detrusor contractile abilities. For this reason, the animal's urination occurs as a result of increased abdominal pressure, not voluntarily.
Non-neurogenic incontinence is due to a decreased ability to sense and/or respond to signals from the nervous system. Anatomic or functional disorders may play a role. Urethral sphincter mechanism incontinence is the most common type and is seen most often in medium- to large-breed spayed or neutered dogs. Therapeutic options include sympathomimetic agents (eg, phenylpropanolamine) and estrogens (eg, estriol, diethylstilbestrol). Gonadotropin-releasing hormone agonist therapy (eg, deslorelin, leuprolide) has been used in dogs successfully and may be a possible treatment for cats in the future (additional testing is being conducted). Combination therapy, including sympathomimetics with estrogens, can also be considered.
Dr. Landis-Hanna, a 2002 graduate of Auburn University, has practiced small animal, exotic, shelter, and relief medicine. She was a medical director at VCA for 7 years and served as Director of Veterinary Medicine for Voyce. She is currently the senior manager of veterinary outreach for PetSmart Charities.