Page 906 - Small Animal Clinical Nutrition 5th Edition

938 Small Animal Clinical Nutrition

ues ranging from 6.5 to 6.9 (Lekcharoensuk et al, 2001a). glomerulations or Hunner’s ulcer. Glomerulations are submu-
VetBooks.ir Although two studies have identified that feeding acidifying cosal petechial hemorrhages, whereas Hunner’s ulcer is a small
area of brownish-red mucosa, surrounded by a network of radi-
foods is associated with calcium oxalate uroliths in cats, addi-
ating vessels. Veterinary investigators report that lesions indis-
tional evaluation is necessary to show a cause-and-effect rela-
tionship and to determine what specific nutritional factors (e.g., tinguishable from glomerulations are observed commonly dur-
magnesium content, degree of acidifying potential) are ing cystoscopic examination of cats with FIC (Osborn et al,
involved. It is of interest to note that normal urinary pH values 1994; Buffington et al, 1997). A single case report describes a
in feral cats are reported to be 5.97 ± 0.10 (range, 5.54 to 6.57) cat with FIC and findings of Hunner’s ulcer (Clasper, 1990).
in females and 6.37 ± 0.07 (range, 5.73 to 7.39) in males The pathogenesis of FIC appears to involve a variety of
(Cottam et al, 2002). Both studies described above evaluated abnormalities affecting the urinary bladder, nervous system and
data collected from 1990 to 1992, when occurrence of calcium hypothalamic-pituitary-adrenal axis (Westropp et al, 2004,
oxalate uroliths was increasing. Since 2001, occurrence of stru- 2005). One study of patients with FIC revealed abnormally low
vite uroliths has been increasing and calcium oxalate has been amounts of urinary glycosaminoglycans (GAG) compared with
decreasing. Therefore, additional study is needed to identify normal controls (Buffington et al, 1996b). In contrast, studies
more current risk factors and causes for recent trends of feline of urinary GAG in human patients with interstitial cystitis have
urolithiasis. It seems likely that multiple factors (e.g., nutrition- yielded variable results (Akcay et al, 1999; Erickson et al, 1997;
al, presence and function of urolith inhibitors, genetic predispo- Hurst et al, 1993). The surface layer covering the urinary blad-
sition) play a role in formation of calcium oxalate uroliths in der mucosa includes GAG. A defective GAG layer or damaged
susceptible cats. urothelium may allow irritating substances in the urine to con-
tact sensory nerve endings, which transmit action potentials
Pathogenesis through the spinal cord to the brain, resulting in perception of
Feline Idiopathic Cystitis pain. In addition, there may be local release of neurotransmit-
The clinical course of FIC is characterized by episodes of lower ters (e.g., substance P) and other inflammatory mediators (e.g.,
urinary tract signs that usually resolve spontaneously within histamine) within the urinary bladder mucosa, which interact
three to five days, with or without treatment (Barsanti et al, with receptors on vessel walls causing vascular permeability and
1982; Gunn-Moore and Shenoy, 2004). Although not evaluat- leakage (i.e., neurogenic inflammation) (Westropp et al, 2005).
ed in a large number of cases, it appears that 39 to 65% of cats Studies have shown that patients with FIC have increased uri-
with FIC will have recurrence of signs within a six- to 12- nary bladder permeability and leakage of ions across the uro-
month period (Barsanti et al, 1982; Markwell et al, 1999; thelium compared with normal cats (Lavalle et al, 2000; Gao et
Kruger et al, 2003; Gunn-Moore and Shenoy, 2004). Many al, 1994; Westropp et al, 2006a). Histologic changes associated
cats have multiple recurrences within a year. In a study involv- with FIC generally are nonspecific and may include an intact or
ing 70 cats with FIC, 63 (90%) had multiple episodes of lower damaged urothelium with submucosal edema, dilatation of
urinary tract signs; 30 (43%) cats had at least three episodes in submucosal blood vessels, submucosal hemorrhage and some-
the year before diagnosis (Buffington et al, 1997). In a study of times increased mast cell density (Westropp et al, 2005).There
15 untreated cats with acute FIC, eight (53%) had one or more is no correlation between histologic lesions, cystoscopic find-
episodes of recurrent signs of lower urinary tract disease with 22 ings and clinical signs in patients with FIC. Cats may have
events reported over a period of 7,942 days at risk (Kruger et al, remission of clinical signs but persistently abnormal cystoscop-
2003).The overall incidence rate was 2.6 events per 1,000 days ic findings (Westropp et al, 2005).
at risk. Survival analysis revealed that increasing number of Several neurohormonal abnormalities have been described in
prior episodes of lower urinary tract signs was associated with a patients with FIC and may play a role in its pathogenesis. A
significantly higher risk, whereas increasing age was associated significant increase in tyrosine hydroxylase immunoreactivity
with a significantly lower risk of recurrence of clinical signs. In was identified in the locus coeruleus (a nucleus in the brain-
another study, cats with FIC experienced a mean of five recur- stem) of patients with FIC compared with findings in healthy
rences in six months (Gunn-Moore and Shenoy, 2004). control cats (Reche Júnior and Buffington, 1998; Welk et al,
FIC shares many features in common with human intersti- 2003). Urinary bladder distention stimulates neuronal activity
tial cystitis and has been called feline interstitial cystitis when in the locus coeruleus, the origin of the descending excitatory
cystoscopic examination reveals characteristic findings (Buf- pathway to the urinary bladder. Tyrosine hydroxylase is the
fington et al, 1997, 1996a, 1996b). Comparisons are based on rate-limiting enzyme involved in synthesis of catecholamines
clinical signs and diagnostic features. All of the National (e.g., norepinephrine). Chronic stress can increase tyrosine
Institutes of Health (NIH) criteria (i.e., history, laboratory hydroxylase activity in the locus coeruleus with subsequent
evaluation, cystoscopy and cystometrics) for interstitial cystitis increases in autonomic outflow. It is possible this may play a
in human patients have been applied to cats (Gao et al, 1994). role in the waxing and waning of clinical signs observed in
Affected people and cats present as adults with symptoms/signs patients with FIC, particularly in response to environmental
of variable severity that are influenced by stress. Spontaneous stressors (Westropp et al, 2005). Patients with FIC also have
remissions occur in people and cats. According to NIH criteria, increased plasma norepinephrine concentrations (Buffington
the diagnosis in people also requires cystoscopic lesions, either and Pecak, 2001; Westropp et al, 2006a). In a study evaluating