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1018 Urolithiasis, Struvite

before complete dissolution and ineffective • Some dissolution diets provide inadequate PROGNOSIS & OUTCOME
dissolution. nutrition for long-term feeding. Calculolytic • Prognosis for dissolution of uroliths is good.
VetBooks.ir (see Nutrition/Diet below) and appropriate • Other diets (e.g., Prescription Diet Multicare • Recurrence of struvite urolithiasis is common.
diet is continued 1 month past radiographic
• For medical dissolution, calculolytic diets
disappearance of uroliths.
antimicrobials are required.
○ Mean time to dissolution is 2-3 months
(2-4 weeks for sterile uroliths, longer time c/d and w/d, Royal Canin SO, Purina UR st/ PEARLS & CONSIDERATIONS
ox, Blue Buffalo WU) aid in the prevention
for nephroliths than for cystoliths). of recurrent struvite urolithiasis and can be Comments
○ Urinalysis and urine culture should be fed long term. • Struvite urolithiasis in dogs is routinely
repeated 5-7 days after initiating medical associated with UTI. Elimination of infection
therapy. Goals are urine pH < 7.0, urine Possible Complications is crucial for dissolution of stones with a
specific gravity of 1.010-1.020, and nega- • Risk of urethral obstruction from small stones calculolytic diet.
tive culture. or during medical dissolution as the stones • Struvite urolithiasis in cats is rarely associated
○ Medical therapy is continued 1 month become small enough to pass into the urethra with UTI; long-term diet modification is
beyond radiographic disappearance of (males) often necessary to prevent recurrence.
uroliths. ○ Urinary tract obstruction • If uroliths fail to resolve with medical therapy,
○ Small uroliths may lodge in urethra ○ Hydronephrosis consider
(especially males) during urolith dissolu- ○ Hydroureter ○ Inadequate infection control
tion. • UTI ○ Failure to comply with diet restrictions
• Mechanical removal of uroliths • Urinary tract polyp formation ○ Mixed or alternative urolith composition
○ Urohydropropulsion (voiding, retrograde • Uroliths inadvertently may be left behind • Struvite crystalluria can be found in normal
[pp. 1175 and 1176]) during surgery (up to 20% of stones are urine and does not reliably predict struvite
Avoid in male cats. not removed). urolithiasis.
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○ Catheter-assisted retrieval • Some diets appropriate for treatment/
○ Cystoscopy-assisted retrieval (p. 1085) prevention of struvite urolithiasis may Prevention
○ Cystotomy/urethrotomy/urethrostomy/ predispose to calcium oxalate urolithiasis. • Dogs: if urinary infection can be eliminated,
pyelotomy/nephrotomy • Malnutrition due to long-term feeding of long-term diet change is not necessary.
○ Lithotripsy (intracorporeal laser lithotripsy certain dissolution diets • Cats: long-term use of canned struvite-
or extracorporeal shock wave lithotripsy) management diets (e.g., Royal Canin SO,
Recommended Monitoring Purina UR st/ox, Prescription Diet c/d
Chronic Treatment • Repeat radiographs q 2-4 weeks during Multicare, Blue Buffalo WU) is best if
• Predisposing causes of UTI should be medical dissolution to evaluate urolith size recurrence noted.
addressed (e.g., control glucosuria in diabetic and number. • The merit of supplementing with glycosami-
animals, treat hyperadrenocorticism). • If no improvement is seen on radiographs noglycans is unknown.
• For animals with recurrent UTI, chronic after 4-8 weeks, mechanical removal is
prophylactic therapy may be considered after indicated. Technician Tips
appropriate therapy of recognized infection • Repeat urinalysis 5-7 days after initiating Any voided urinary stone should be saved for
(p. 232). medical dissolution therapy to ensure pH analysis.
• Promote water consumption to avoid between 6.5 and 7, specific gravity between
concentrated urine (e.g., canned food, 1.010 and 1.020 (dogs) or 1.030-1.040 (cats) Client Education
wetting dry food, use of cat water fountains absent struvite crystals, and absent bacteruria. • Adherence to dietary therapy must be strict
[p. 332]). • Ideally, urine culture is repeated 5-7 days in cases of sterile struvite urolithiasis.
• Dietary therapy is crucial for sterile struvite after initiating medical dissolution therapy • Prevention of UTI is the most important
urinary stones (see Nutrition/Diet below). to ensure sterile urine. preventative measure for most dogs.
• Urinary acidifiers are seldom required if the • Repeat urine culture 5-7 days after stopping • Urethral obstruction is life-threatening. Stran-
pet is eating an appropriate diet and urinary antibiotics to assess recurrence of infection, guria should prompt immediate veterinary
tract infection is eliminated. then again 3-4 weeks later. attention.
• If predisposing causes of bacterial cystitis
Nutrition/Diet cannot be corrected or in animals with sterile SUGGESTED READING
• Many commercial diets (e.g., Hill’s Prescrip- struvite urolithiasis, repeat urinalysis q 4-6 Lulich JP, et al: ACVIM Small Animal Consensus
tion Diet s/d, Royal Canin SO, Purina UR months. Recommendations on the Treatment and Prevention
st/ox, Blue Buffalo WU) are designed to aid • If predisposing causes of bacterial cystitis of Uroliths in Dogs and Cats. J Vet Intern Med
struvite urolith dissolution. cannot be corrected or in animals with 30:1564-1574, 2016.
• Monitor urolith size periodically by radio- sterile struvite urolithiasis, repeat abdominal AUTHOR: Joseph W. Bartges, DVM, PhD, DACVIM,
graphs (see Recommended Monitoring radiographs initially q 3-6 months for 1 year, DACVN
below). then q 6 months thereafter. EDITOR: Leah A. Cohn, DVM, PhD, DACVIM

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