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Urolithiasis, Urate 1019

Urolithiasis, Urate Bonus Material Client Education
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VetBooks.ir Etiology and Pathophysiology Diseases and Disorders
BASIC INFORMATION
• Due to congenital PSS, miniature schnauzers,
shih tzus, and Yorkshire terriers are also • Dalmatians
Definition overrepresented for having urate stones. ○ During protein catabolism in non-
Urinary tract stones (uroliths) composed of uric Dalmatian dogs, purine metabolism leads
acid and its salts (usually ammonium urate) RISK FACTORS to uric acid oxidation by hepatic uricase,
comprise approximately 5%-10% of uroliths in • PSS (p. 814) producing allantoin (excreted in urine).
dogs (except Dalmatians and English bulldogs) • Hepatic MVD (p. 655) ○ Despite normal uricase activity, Dalmatians
and cats. • Hepatic cirrhosis (p. 174) convert uric acid to allantoin inadequately,
• Acidic urine and/or urinary infection with resulting in increased urinary excretion of
Synonyms urease-producing bacteria poorly soluble uric acid.
Purine urolithiasis, ammonium urate urolithia- • Breed and SLC2A9 mutation ○ This occurs due to a mutation in the
sis, uric acid urolithiasis, urate calculi/stones SCL2A9 gene that encodes for a hepatic
ASSOCIATED DISORDERS transporter of uric acid. HUA Dalma-
Epidemiology • Urinary tract infection tians and urate urolith–forming English
SPECIES, AGE, SEX • Ureteral or urethral obstruction bulldogs and Black Russian terriers are
• Most often seen in young to middle-aged • Liver disease (see Risk Factors) homozygous recessive for this mutation.
adult dogs and young adult cats • Dogs with hepatic dysfunction: reduced
• Urate uroliths are the most common urolith Clinical Presentation uricase function and increased renal excretion
of Dalmatian dogs (≈35% of Dalmatians HISTORY, CHIEF COMPLAINT of uric acid and ammonia resulting from
form urate uroliths) and occur predominantly Clinical signs often absent. When apparent, reduced hepatic conversion/urea synthesis
in 3- to 4-year-old males. may include • Non-Dalmatian, non–English bulldog,
• English bulldogs: ≈50% of uroliths in this • Pollakiuria non–Black Russian terriers, and cats without
breed composed of urate, ≈50% cystine • Hematuria hepatic dysfunction: unknown
• Second most common mineral in uroliths • Inappropriate elimination (periuria)
from neonatal dogs and cats (after infection- • Stranguria, dysuria DIAGNOSIS
induced struvite) • If PSS and/or MVD is present, growth
• Neonatal/young adult dogs and cats with retardation Diagnostic Overview
portosystemic shunts (PSSs) or hepatic • If hepatic dysfunction is present, encepha- Diagnosis is suspected in dogs with radiolucent
microvascular dysplasia (MVD). lopathy and/or hypoglycemia (e.g., altered uroliths and a breed predisposition or hepatic
mentation, seizures) dysfunction. Diagnosis in cats and healthy dogs
GENETICS, BREED PREDISPOSITION • Systemic illness due to urinary obstruction of other breeds is usually based on quantitative
• High uric acid (HUA) Dalmatians (non– stone analysis.
back-crossed) are unique in their excretion PHYSICAL EXAM FINDINGS
of uric acid instead of allantoin as an end Physical exam is usually unremarkable. Abnor- Differential Diagnosis
product of purine metabolism, but only malities may include • Urinary tract infection
a subset develops urate urolithiasis. The • Hematuria (stains on prepuce, vulva, • Other types of uroliths
tendency to form uroliths is heritable, hocks) • Urinary tract neoplasia
although the genetics are incompletely • Palpable cystic calculi
understood. Back-crossed Dalmatians may • Palpable urethral calculi (by digital rectal Initial Database
be homozygous or heterozygous low uric exam in dogs) • CBC: often unremarkable, but PSS is associ-
acid (LUA) excreters; only homozygous HUA • Enlarged, turgid bladder if urethral obstruc- ated with microcytosis.
dogs are HUA excreters. tion present • Serum biochemical profile: often unremark-
• Predisposed non-Dalmatian breeds include • ± Signs of PSS, MVD, hepatic encephalopa- able but may suggest hepatic dysfunction
English bulldogs and Black Russian terriers. thy (p. 440) (pp. 174 and 814). Urinary tract obstruction

A B

UROLITHIASIS, URATE Plain lateral abdominal radiograph (A) and double-contrast cystogram (B) show urate cystic calculi.
Note the cranial displacement of the axis of the stomach, indicating microhepatica. This dog had an extrahepatic portosystemic
shunt. The urethral catheter (containing air and positive contrast) in this male dog is seen as an incidental observation.

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