Page 912 - Small Animal Clinical Nutrition 5th Edition

944 Small Animal Clinical Nutrition

hematuria result. A more rigid plug forms in the presence of
VetBooks.ir crystals that may cause urethral obstruction. The mineral com-
position of crystals can serve as the basis for preventive efforts.
This process of plug formation has been compared with the
formation of casts in renal tubular lumina. Urinary mucopro-
tein provides a gel that traps intact cells (producing cellular
casts) or disintegrating cellular elements (producing granular
casts). A more trivial analogy is the creation of fruit gelatin
(Figure 46-14).The “gelatin” (i.e., matrix) traps pieces of “fruit”
(i.e., crystals) as it forms.

Urinary Tract Infection
BACTERIAL INFECTION
Infection with urease-producing bacteria (e.g., Staphylococcus
spp. and Proteus spp.) causes persistently alkaline urine, which
may be associated with formation of struvite uroliths. It appears
Figure 46-12. Note urethral plug (white arrow) extruding from the tip that most cats with struvite uroliths do not have UTI; howev-
of the penis in a cat with urethral obstruction. Most urethral plugs er, urolith-induced changes in host-defense mechanisms may
are soft, compressible, friable and composed of large amounts of lead to bacterial colonization of the urinary tract (Osborne et al,
matrix mixed with smaller amounts of crystalline minerals. Although
urethral plugs are diagnosed more often in male cats, due to occur- 1996a). Thirty percent of feline patients with urocystoliths in
rence of urethral obstruction, they also may occur in female cats. one study had positive urine cultures (Osborne et al, 1990). In
a study of uroliths from 150 cats, investigators cultured bacteria
from a urolith or urine in 30 (41%) of 74 cats. Coagulase-pos-
itive staphylococci were cultured from uroliths or urine in 17
cats, representing 45% of bacteria isolated (Ling et al, 1990). In
some cases, culture of urine may be negative or yield the same
or different organisms than cultures from uroliths.
Although a cause-and-effect relationship has not been estab-
lished, there is an increased occurrence of UTI in cats with sys-
temic diseases. Of cats with chronic kidney disease, 10 to 50%
are reported to have UTI; it isn’t known if kidney disease caus-
es UTI or if other factors (e.g., older age) are responsible
(Lulich et al, 1992; McMahon et al, 2006; Mayer-Roenne et al,
2007). UTI also has been reported to occur in 12 to 13% of cats
with diabetes mellitus and 12% of cats with hyperthyroidism
(Bailiff et al, 2006; Mayer-Roenne et al, 2007).
Perineal urethrostomies are associated with significant post-
operative sequelae, including urethral strictures, bacterial UTI
and struvite urolithiasis (Osborne et al, 1991; Griffin et al,
Figure 46-13. Unifying concept for pathogenesis of feline lower uri-
nary tract disease. Infection or inflammation (e.g., idiopathic cystitis) 1992; Bass et al, 2005). These postoperative sequelae can pro-
results in clinical signs of lower urinary tract disease and production duce lower urinary tract signs. In a prospective clinical study of
of excess matrix. Persistent crystalluria can combine with matrix to 30 male cats with intraluminal urethral obstruction and nega-
form urethral plugs or contribute to urolith formation and typical clin-
tive urine cultures, investigators randomly assigned cats to re-
ical signs. (Adapted from Osborne CA, Kruger JM, Lulich JP. Feline
ceive one of three treatments following relief of the obstruction:
lower urinary tract disorders: Definition of terms and concepts.
Veterinary Clinics of North America: Small Animal Practice 1996; 76: 1) nutritional management with a struvite dissolution food, 2)
169-179.) perineal urethrostomy or 3) nutritional management and per-
ineal urethrostomy. During the one-year followup period, none
of the cats receiving nutritional management alone had epi-
Formation of matrix-crystalline urethral plugs hypothetical- sodes of UTI, whereas episodes of bacterial UTI were docu-
ly requires two simultaneous but unrelated events (Figure 46- mented in 50% of the group managed by surgery alone, and
13) (Osborne et al, 1992, 1996b, 1996c). One event is the for- 40% of the group receiving nutritional management and sur-
mation of matrix that may result from some inflammatory gery. Three of the infected cats from the urethrostomy-only
process (e.g., idiopathic, bacterial or viral UTI). The other group subsequently developed urocystoliths (Osborne et al,
event is the formation of crystalline precipitates, most often 1991). In a more recent study, one-year followup of 39 cats that
struvite. If matrix forms without concomitant crystals, the non- had perineal urethrostomy revealed that 51.3% had complica-
crystalline gel is voided; however, nonobstructive dysuria and tions (UTI in nine, stricture in two) or recurrent signs due to