Page 1193 - Clinical Small Animal Internal Medicine

123 Urolithiasis in Small Animals 1131

defect(s) in most cystinuric breeds of dogs have yet to be crops. Plant sources implicated in silicate urolithiasis
VetBooks.ir identified. More recently, Labrador retrievers were found include rice and soybean hulls and corn gluten feed.
Silicates may be high in certain home‐made diets and in
to have a different mutation in the same gene, encoding
for a renal basic amino acid transporter. DNA‐based
may contain high concentrations of silicate so consump­
genetic tests are available to detect abnormal cystine some groundwater from aquifers. In certain regions, soil
excretion for some breeds of dogs. tion of dirt and grass (pica) should be discouraged.
Type II cystinuria is an autosomal dominant disease Experimentally, beagle dogs consuming large quanti­
that has been reported in Australian cattle dogs, border ties of antacids containing magnesium trisilicate were
collies (type II‐a) and miniature pinscher (type II‐b). In predisposed to silica uroliths. Homeopathic, other medi­
the latter, the mutation affects the SLC7A9 gene and cations and vitamin‐mineral supplements may contain
encodes for intramembrane transporter protein. silica, for example silica is used in anticaking materials
The molecular basis for androgen‐dependent type added to tablets.
(type III) cystinuria is unknown. Type III cystinuria
regroups several breeds of dogs such as the English bull­
dog, English mastiff, French bulldog. Type III cystinuria Other Types of Urolithiasis
is typically detected later in life, is less severe clinically, In dogs, mixed composition uroliths comprised 2.3% of
and appears to involve only males. Castration seems to uroliths submitted to the MUC, with an additional 8.8%
lower cystine excretion, therefore the mode of inherit­ of uroliths being described as compound. Compound
ance is unclear. No gene mutation has been identified as uroliths are likely to form when factors initially promot­
the cause of type III cystinuria. ing precipitation of one type of mineral are replaced by
Etiopathogenesis of cystine in cats is not well charac­ factors promoting precipitation of a different mineral.
terized, but one study recently reported an SLC3A1 This can make compound uroliths poorly responsive to
mutation causing cystinuria in a cat as well as three dif­ medical management due to the need to treat each min­
ferent SLC7A9 gene variants in four cats. eral type separately for dissolution or prevention.
Resources for cystinuria testing (urine nitroprusside/ The list below includes uncommon types of uroliths
genetic testing) can be found at PennGen Laboratories: submitted to major urolith centers.
http://research.vet.upenn.edu/penngen
Suture induced: some stones can be induced by residual
●
or retained suture material. Uroliths typically have a
Silicate Urolithiasis piece of suture contained within the stone, or have a hole
Epidemiology where the suture was located (Figures 123.7 and 123.8).
Silica (silicon dioxide) uroliths are infrequently diag­ ● Dried solidified blood calculi: calculi composed solely
nosed. They account for 0.9% of specimens submitted to of dried solidified blood have been removed from the
the MUC and 0.7% of specimens submitted to the CVUC urinary tract of cats.
between 2009 and 2012 (see Table 123.2). Silica‐contain­
ing nephroliths are rarely submitted to urolith centers,
but have been reported in native Kenyan dogs.
Some silica uroliths are pure, while others are composed
of different layers, with oxalate and struvite being the most
commonly associated minerals. Most silica uroliths have a
“jackstone” appearance; however, an outer layer (coating)
of another mineral type may mask this configuration.
Typically, multiple silica uroliths present and cross‐sec­
tion of the urolith usually reveals laminations.
The majority of dogs with silica uroliths are male, with
a mean age of 7.2 +/‐ 3.1 years (range 1–17 years).

Etiopathogenesis
Silica uroliths are thought to form due to individual ani­
mal increase in consumption of this mineral. Animal
protein contains very low concentrations of silica and Figure 123.7 Suture‐induced stone removed from the bladder of
consumed dietary sources are likely plant origin, such as a 7‐year‐old male neutered Yorkshire terrier. Source: Courtesy of
direct ingestion of soil or ingestion of contaminated Andrew Moore, Canadian Veterinary Urolith Centre.