Page 937 - Small Animal Clinical Nutrition 5th Edition

Feline Lower Urinary Tract Diseases 969

spermatozoa) and microorganisms (e.g., bacteria and viruses).
One hypothesis suggests that formation of matrix by infectious or inflammatory agents in cats with concomitant crystalluria
VetBooks.ir of any type may lead to formation of matrix-crystal urethral plugs. Crystalluria per se is unlikely to cause production of large
quantities of matrix because classic uroliths, which are composed of at least 90% crystalline material, contain relatively little
matrix.
3. Risk factors associated with formation of struvite crystals found in urethral plugs are probably similar to those associated with
formation of struvite uroliths. Factors of major therapeutic importance include nutritional factors affecting urine magnesium con-
centration and urinary pH and anything that predisposes to urinary tract infection with urease-producing microorganisms.
4. In general, the immediate need to remove urethral plugs within hours precludes attempts to induce their dissolution over a peri-
od of days or weeks. However, it is often possible to repulse urethral plugs into the urinary bladder lumen. Although urethral
plugs contain markedly greater quantities of matrix than do uroliths, medical protocols that dissolve sterile struvite uroliths would
probably also be effective for dissolving the struvite crystalline component of urethral plugs located in the urinary bladder lumen.
However, such therapy may not result in dissolution of plug matrix. In addition, it must be emphasized that calcium oxalate, cal-
cium phosphate and ammonium urate crystals are occasionally identified in some naturally occurring feline urethral plugs.
Attempts to dissolve struvite crystals by promoting formation of acidic urine should not be initiated in cats with postrenal
azotemia. The metabolic sequela of urethral obstruction, particularly severe metabolic acidosis, should be corrected before phar-
macologic agents or foods designed to acidify urine are used.
5. Perineal urethrostomies can minimize recurrent obstruction of the penile urethra of patients unresponsive to nonsurgical thera-
peutic and prophylactic management. In a prospective study of 30 cats with struvite crystalline-matrix urethral plugs, perineal
urethrostomy and nutritional management were equally effective in their ability to prevent recurrent urethral obstruction.
However, 16 episodes of bacterial urinary tract infection developed in nine cats with perineal urethrostomies; bacterial urinary
tract infections were not observed in cats treated only with nutritional management. Furthermore, staphylococcal-induced stru-
vite urocystoliths developed in two cats with perineal urethrostomies. In another study of cats that had perineal urethrostomy,
over half developed complications (urinary tract infection, stricture) or had recurrent clinical signs due to urolithiasis or FIC.
These observations emphasize that perineal urethrostomies may be associated with significant short-term and long-term com-
plications. Localization of the site(s) and cause(s) of urethral obstruction is especially important if urethrostomy is considered.

Progress Notes
To further characterize the composition of the urethral plug and identify potential etiopathologic factors, a portion of the urethral
plug was obtained and submitted for light and electron microscopic examination and quantitative mineral analysis. Light micro-
scopic evaluation of the urethral plug revealed that it was composed of numerous unorganized crystals, occasional white blood cells
and large quantities of amorphous matrix (Figure 1). Electron microscopy did not reveal any specific etiologic agents. Subsequent
quantitative mineral analysis revealed that the crystalline component of the plug was composed of 100% struvite.
Urethral patency was reestablished with a combination of procedures that included: 1) gentle massage of the distal urethra fol-
lowed by gentle compression of the urinary bladder, 2) partial decompression of the bladder by cystocentesis and 3) flushing of the
urethral lumen with sterile 0.9% saline solution. After urine flow was restored, particulate material in the urinary bladder was
removed by lavage of the bladder lumen with sterile saline solu-
tion. Because the large quantity of urine precipitates in the blad-
der lumen represented a potential risk factor for reobstruction, a
sterile indwelling red-rubber urinary catheter was placed and
connected to a closed sterilized drainage system. Systemic fluid
and acid-base imbalances associated with obstructive uropathy
were corrected over a 24-hour period by intravenous administra-
tion of lactated Ringer’s solution.
Gross hematuria gradually subsided over 48 hours. The
indwelling urinary catheter was removed and the cat was
observed for signs of reobstruction. Aerobic bacteria were not
detected on followup quantitative culture of urine collected via
the indwelling catheter before its removal.
The cat was fed a commercial veterinary therapeutic food
designed to promote dissolution of the struvite crystal component
a
of the urethral plug (Prescription Diet s/d Feline ). When the cat Figure 1. Photomicrograph of a urethral plug removed from a four-
was discharged from the hospital, its owner was instructed to feed year-old, castrated male, mixed-breed cat with obstructive uropa-
the food in sufficient quantity to maintain stable body weight thy. Note spaces previously occupied by struvite crystals sur-
rounded by large quantities of amorphous matrix containing white
(approximately 320 kcal [1,339 kJ]; 2/3 cup). Analysis of a urine
blood cells (toluidine blue stain; 100X original magnification).
sample collected 20 days after initiation of nutritional therapy