Page 1186 - Clinical Small Animal Internal Medicine

1124 Section 10 Renal and Genitourinary Disease

in clinical signs related to uremia, unless there is con­
VetBooks.ir tralateral kidney disease.
Systemic disease signs, such as fever, weight loss or
dehydration, associated with uremia may be present
dependent on functionality of the renal parenchyma and
the presence of infection. Flank pain may be present with
ureteral obstruction or infection.

Patient Signalment Related
to Specific Stone Types

In dogs and cats, signalment (breed, sex, age) and geo­
graphic region can provide clues to urolith composition
(Tables 123.1, 123.2).
Figure 123.1 One canine oxalate urolith from a 12‐year‐old
female spayed miniature schnauzer. Source: Courtesy of Andrew Oxalate Urolithiasis
Moore, Canadian Veterinary Urolith Centre.
Calcium oxalate uroliths are usually composed of 100%
calcium oxalate, although some also contain varying
of systemic disease may be noted (e.g., vomiting, lethargy, amounts of calcium phosphate. Additionally, concurrent
anorexia, polyuria‐polydipsia secondary to uremia, etc.), infection can change the composition of the stone, for
which can range in severity, as related to secondary infec­ example calcium oxalate nidus encased in struvite shell.
tion or complete urethral obstruction. Other patients Two crystalline forms of calcium oxalate uroliths can
may have subclinical disease, that is, no signs, and either occur: calcium oxalate monohydrate (whewellite) and
upper or lower urinary tract uroliths are discovered inci­ calcium oxalate dihydrate (weddellite). Calcium oxalate
dentally, for example via radiographs, ultrasound, etc. monohydrate is more frequent in canine uroliths than
calcium oxalate dihydrate.
Physical Examination Findings The surface characteristics of oxalate uroliths can vary
widely; uroliths may be smooth, mulberry shaped or have
Physical examination is frequently normal but dependent sharp projections (Figure 123.2; see also Figure 123.1).
on stone type and, more importantly, location, abnor­
malities associated with either the lower or upper urinary Epidemiology and Risk Factors
tract can occur and are detailed below. Systemic signs Calcium oxalate uroliths represented 48.1% (49.5%
(i.e., fever, dehydration, etc.) can be found in patients including mixed stones) of all canine and feline uroliths
with secondary infections or obstructive disease. submitted to the Canadian Veterinary Urolith Centre
(CVUC) from 2009 to 2014 (see Table 123.2). Most upper
Lower Urinary Tract Urolith Physical Exam Findings urinary tract uroliths in cats (98%) and half of those
Palpation of urinary calculi can be challenging, particu­ found in dogs are composed of calcium oxalate.
larly in overweight or tense patients. If the bladder is Although calcium oxalate stones are not considered
empty and there are multiple stones, a crepitant sensa­ infection induced, they may be associated with secondary
tion may be noted on bladder palpation. Urethral stones urinary tract infections (UTI). This is because the presence
can sometimes be palpated rectally or via palpation of the of the uroliths is believed to affect the patient’s local immune
perineum or penile urethra. A large firm bladder may be defenses. In one study, 52% of female dogs and 31% of male
suggestive of urethral obstruction. However, in the case dogs with calcium oxalate urolithiasis were found to have
of uroabdomen, the bladder may be empty (not palpable), concurrent bacteria present, that is, positive urine or uro­
and the patient may have a tense and painful abdomen. lith cultures. However, other studies have not supported an
association between calcium uroliths and UTI.
Upper Urinary Tract Urolith Physical Exam Findings Risk factors for calcium oxalate uroliths in dogs include
The patient may be subclinical. An enlarged kidney may sex, and they occur more commonly in male than female
be palpated with hydronephrosis associated with ure­ dogs. Additionally, neutered male dogs have an increased
teral obstruction in dogs and cats; however, most cats risk of calcium oxalate uroliths compared with intact
have chronically small kidneys, even with obstruction. males. Obese dogs are more likely to form calcium oxa­
Unilateral renal or ureteral obstruction should not result late uroliths, which is similar to cats and humans.