Page 936 - Small Animal Clinical Nutrition 5th Edition

968 Small Animal Clinical Nutrition

CASE 46-1
VetBooks.ir Obstructive Uropathy in a Cat

John M. Kruger, DVM, PhD, Dipl. ACVIM (Small Animal Internal Medicine)
College of Veterinary Medicine
Michigan State University
East Lansing, Michigan, USA

Patient Assessment
A four-year-old, castrated male, mixed-breed cat was examined for acute dysuria, pollakiuria and stranguria. The cat had one pre-
vious episode of obstructive uropathy approximately 18 months earlier. No other historical problems were identified.
Physical examination revealed that the cat was depressed, lethargic and approximately 5% dehydrated. Temperature was normal.
Heart and respiratory rates were increased. The cat weighed 6.4 kg and was considered overweight (body condition score 4/5).
Abdominal palpation revealed a firm, painful and overly distended urinary bladder. A small plug of tan, gritty material was identi-
fied at the level of the external urethral orifice.
Analysis of a urine specimen collected by cystocentesis revealed moderately concentrated urine with a neutral pH, struvite crys-
talluria and findings typical of inflammation (i.e., hematuria, pyuria and proteinuria). Aerobic bacteria were not detected by quan-
titative urine culture. Results of a hemogram were within normal limits. A serum biochemistry profile revealed mild azotemia.
Venous blood gas measurement identified a mild metabolic acidosis. Survey abdominal radiographs revealed increased amounts of
intraabdominal fat and an overly distended urinary bladder.

Assess the Food and Feeding Method
The cat had been fed a dry commercial maintenance food free choice, which was supplemented with a small amount of moist com-
mercial maintenance food (one tablespoon, once daily). The cat had unlimited access to fresh water.

Questions
1. What are potential causes of urethral obstruction in male cats?
2. What differences exist between uroliths and urethral plugs?
3. What are risk factors for formation of struvite crystals?
4. Can nutritional management dissolve urethral plugs?
5. What is the effectiveness of perineal urethrostomy vs. medical therapy for preventing recurrent urethral obstruction due to stru-
vite-containing urethral plugs?

Answers and Discussion
1. Urethral obstruction may be caused by one or more intramural, mural or extramural abnormalities located at one or more sites.
In a prospective study of urethral obstruction in 51 male cats, investigators identified crystalline-matrix urethral plugs in 59% of
cats; urethroliths were identified in 12% of cats and a specific cause could not be identified in 29% of affected cats. In a prospec-
tive study of European cats, 45 of 67 male cats with signs of lower urinary tract disease had urethral obstruction; most common
causes included feline idiopathic cystitis (FIC) (24 cats), uroliths (13 cats) and urethral plugs (eight cats). Other possible causes
of urethral obstruction include sloughed tissue fragments originating from the bladder or urethra, acquired urethral strictures,
prostatic lesions, urethral neoplasms, periurethral neoplasms, congenital urethral anomalies and functional urethral obstruction
(e.g., reflex dyssynergia).
2. There are distinct physical and probable etiopathogenic differences between feline uroliths and urethral plugs; therefore, these
terms should not be used synonymously. Uroliths are highly organized polycrystalline concretions composed primarily of miner-
als (organic and inorganic crystalloids) and smaller quantities of nonmineral matrix. In contrast, most feline urethral plugs are
composed of relatively large quantities of matrix mixed with mineral crystals. However, some urethral plugs are composed pri-
marily of matrix, some consist of sloughed tissue, blood and/or inflammatory reactants and a few are composed primarily of
aggregates of crystalline minerals. In general, feline crystalline-matrix urethral plugs appear as cylindrical concretions that con-
form to the diameter of the urethra and vary from a few mm to several cm. They usually are soft, friable, easily compressed and
have no visible organized external structure. Urethral plugs contain varying quantities of minerals in proportion to large quanti-
ties of matrix. Struvite is the most common mineral type identified in feline urethral plugs. However, a variety of different min-
eral types (e.g., calcium oxalate, ammonium urate, calcium phosphate) have been identified in urethral plugs of cats, suggesting
that multiple risk factors are involved in their formation.
The matrix component of feline urethral plugs is less well defined. Studies in cats and other species suggest that matrix is het-
erogeneous and may be composed of mucoproteins, albumin, globulins, cells (e.g., erythrocytes, leukocytes, epithelial cells and