Page 2033 - Cote clinical veterinary advisor dogs and cats 4th

Urolithiasis, Oxalate 1015

renal excretion of calcium, or increased ○ Shape varies from spiculated (dihydrate) • Mechanical removal of bladder/urethral
resorption of calcium from bone with or to smooth (monohydrate). The perineum calculi producing clinical signs; radiographs
VetBooks.ir • Hypercalcemia is identified in 20%-35% of Advanced or Confirmatory Testing complete removal. Diseases and Disorders
must be included in the radiographic field
without hypercalcemia.
should be repeated afterward to ensure
to identify uroliths in the urethra.
cats and ≈4% of dogs with calcium oxalate
○ Urohydropropulsion (voiding, retrograde
urolithiasis. Hypercalcemia in cats with
calcium oxalate uroliths is usually idiopathic • Abdominal ultrasound: little benefit beyond [pp. 1175 and 1176]); avoid performing
voiding urohydropropulsion in male cats.
in nature; hypercalcemia in dogs with abdominal radiography but can confirm ○ Catheter-assisted retrieval
calcium oxalate uroliths is usually associated location, assess kidneys for evidence of ○ Cystoscopic-assisted retrieval (p. 1085)
with primary hyperparathyroidism. pyelonephritis or hydronephrosis ○ Cystotomy/urethrotomy/urethrostomy/
• Hyperadrenocorticism associated with • Urolith analysis: retrieved stones should pyelotomy/nephrotomy/ureterectomy
calcium oxalate uroliths in dogs may or be submitted for quantitative analysis with neoureterocystostomy, ureteral stent,
may not be associated with hypercalcemia. (crystallography, x-ray diffraction, infrared or subcutaneous ureteral bypass device
• Hyperoxaluria in cats may be related to diet, spectroscopy) to determine urolith type. implantation
inadequate vitamin B 6 , and hepatic enzyme • Urolith culture: if urine culture by cysto- ○ Lithotripsy, intracorporeal or extracorporeal
deficiencies. centesis is negative shock wave lithotripsy
• Urolith formation is potentiated by • Cystoscopy with or without laser lithotripsy • Calcium oxalate is the most common type
diminished concentrations of urinary may facilitate stone removal for analysis and of nephrolith/ureterolith. Because surgical
crystallization inhibitors (e.g., nephrocalcin, therapy (p. 1085). removal of nephroliths can reduce renal func-
citrate, pyrophosphate, glycosaminoglycans, • Specific diagnostic tests may be indicated to tion (p. 689), it is not uniformly indicated.
Tamm-Horsfall mucoprotein). identify predisposing conditions (e.g., ionized
• Diets with moderate fat and carbohydrate calcium concentration, parathyroid hormone Chronic Treatment
levels: increased risk of calcium oxalate stone assay, adrenal function testing). • Identify underlying disorder (e.g., hyperadre-
formation (vs. diminished risk for diets high nocorticism, hyperparathyroidism) if present,
in moisture with a moderate magnesium, TREATMENT and treat appropriately.
phosphorus, and calcium content) • For cats with idiopathic hypercalcemia,
Treatment Overview high-fiber diet may be beneficial. To simul-
DIAGNOSIS Urethral obstruction requires immediate relief. taneously alkalinize the urine, add potassium
Oxalate stones cannot be dissolved with medical citrate 75 mg/kg PO q 12h, adjusted so urine
Diagnostic Overview therapy, and uroliths in the bladder or urethra pH = 6.5-7.0. Bisphosphonates (alendronate)
Diagnosis is suspected in animals with should be removed mechanically if they are may help control hypercalcemia: initially
radiopaque bladder stones and acidic urine causing clinical signs. Recurrence is common 2 mg/kg PO once weekly. Most cats respond
or in animals with radiopaque nephroliths. (up to 50% in 3 years in dogs). to 10 mg/CAT. Follow with at least 6 mL
Quantitative stone analysis is necessary for con- of water PO after administration, and
firmation and an optimal treatment/prevention Acute General Treatment butter the lips to increase salivation and
plan. More than 50% of patients with active • Relieve urethral obstruction (pp. 1175 and increase transit. Effects, if seen, occur in
calcium oxalate uroliths do not have concurrent 1176). 3-4 weeks. Monitor serum ionized calcium
crystalluria. A global approach to diagnosis and • Antibiotics (choice based on culture and (p. 491).
management is outlined on p. 1455. susceptibility) if secondary UTI • Initiate measures to prevent recurrence (see
• If uroliths are found incidentally in the Prevention below).
Differential Diagnosis absence of clinical signs, it is reasonable
• UTI, bacterial or fungal (p. 232) to omit removal and begin prevention to Nutrition/Diet
• Other types of uroliths minimize growth of uroliths, including • Avoid calcium supplements, acidifying diets,
• Urinary tract neoplasia (p. 991) regular follow-up for urinalysis, urine culture, and foods high in oxalate such as green leafy
and radiography. vegetables.
Initial Database
• CBC: unremarkable
• Serum biochemistry profile (including
electrolytes) typically unremarkable
○ Hypercalcemia or evidence of endocri-
nopathy: uncommon
○ Azotemia, hyperkalemia, metabolic
acidosis if urinary tract obstruction
• Urinalysis: acidic to neutral pH unless UTI;
crystalluria (< 50%); hematuria and/or pyuria
(occasional)
○ Storage of urine may lead to precipitation
of oxalate crystals (artifact); urine sediment
should be examined within 1 hour of
collection.
○ Urine bacterial culture and susceptibility
to rule out secondary infection
• Abdominal radiographs: radiopaque calculi
most commonly located in bladder, some- UROLITHIASIS, OXALATE Lateral abdominal radiograph of a dog with two large, irregular, mineral-opacity
times urethra, ureter, or renal pelvis structures (large arrows) in the urinary bladder that are consistent with oxalate uroliths. A mineral opacity in the
○ Relative radiopacity of uroliths: struvite region of a ureter (small single arrow) and mineral opacities in both kidneys (small arrows) are also consistent
≥ oxalate = CaPO 4 ≥ silica > cystine with oxalate urolithiasis, but a dorsoventral or ventrodorsal view is necessary to differentiate ureterolithiasis
> urate from mineral in the gastrointestinal tract.

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