Nephrolith management in Cats and Dogs

Nephrolith management in Cats and Dogs

When NOT to ignore?

Diagnosis:

  • Radiographs: size, number and clues about the type of nephrolith present
  • Abdominal ultrasound: evaluate pyelectasia, ureteral obstruction
  • Blood work- ionized calcium, bile acids as indicated
  • Urinalysis: helps with diagnosis of stone type and monitoring medical management
  • Urine culture: essential in management and prevention of recurrence

Medical Management:

  • Struvite: Dissolution diet and long-term antibiotics
    • Can take up to a year to fully dissolve stones
  • Calcium oxalate: Prevent with diet, dilution, vitamin B6, potassium citrate
  • Others: cysteine vs. urate

When to intervene?

  • Chronic urinary tract infections
  • Worsening azotemia
  • Massive stones causing renal parenchymal damage
  • Ureteral obstruction(s)
  • Hematuria
  • Pain/discomfort

Traditional interventions:

  • Surgical Nephrolithotomy: known to decrease renal function in both cats and dogs post-operatively
  • Nephrotomy: not ideal as want to maintain/preserve kidney function
  • Pyelectomy: potential for obstruction and scar formation

Minimally invasive interventions:

  • ESWL: Extracorporeal Shock-wave Lithotripsy
    • 85% successful stone removal
    • 30% need repeated procedures, 10% have ureteral obstructions
    • Can cause renal damage in dogs
    • Not suitable in cats due to mobility of kidneys
    • Does not fracture cystine stones
  • ENL: Endoscopic guided nephrolithotomy
    • Standard of care in human medicine for complex nephroliths
    • Reduced nephron damage, complete stone removal, ureteral stent placement to prevent ureteral obstructions
    • Well tolerated, minimal morbidity and no mortality
    • 100% successful stones removal
    • Ureteral stents placed at the time of procedure- 0% occurrence of ureteral obstruction

Follow-up management:

  • Serial radiographs: 1/month after procedures then every 3 months for 1 year and every 6 months for life.
  • Serial urine cultures and urinalyses

Pre-ENL VD radiograph in a dog, showing of a struvite calcium apatite nephrolith
Pre-ENL VD radiograph in a dog, showing of a struvite/calcium apatite nephrolith.

VD radiographs following ENL showing absence of stone and ureteral stent in place

VD radiographs following ENL showing absence of stone and ureteral stent in place.

Shown below is a schematic image of kidney with and percutaneous access with a sheath to allow access via endoscopy in order to remove stones. Nephroscopes are typically used with specialized lithotripsers to simultaneously break up and suction fragments of large stones.

percutaneous-nephrolithotomy

If you would like more information please contact: Dr. Erinne Branter, BVSc, DACVIM
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References:
Branter, EB, Berent, AB,, Weisse, CW. Endoscopic assisted nephrolithotomy in cats and dogs. Abstract presented at ACVIM forum 2012.
Block, G. , Adams, LG, Widmer, WG et al. Use of extracorporeal shock wave lithotripsy for treatment of spontaneous nephrolithiasis and ureterolithiasis in dogs. J Am Vet Med Assoc, 208 (1996):531-536.
Goldman, CK, et al. Extracorporeal shock-wave lithotripsy for the treatment of urocystoliths in dogs (Abstract). Urol Res 36;179.
Raza A, Turna B, Smith G, et al. Pediatric urolithiasis: 15 years of local experience with minimally invasive endourological management of pediatric calculi. J Urol 2005;174(2):682-685.
Donner GS, Ellison GW, Ackerman N, et al. Percutaneous nephrolithotomy in the dog: An experimental study. Vet Surg 1987;16(6): 411-417.
Al-Shammari AM, Al-Otaibi K, Leonard MP, et al. Percutaneous nephrolithotomy in the pediatric population. J Urol 1999;162(5):1721-1724.
Lennon GM, Thornhill JA, Grainger R, et al. Double pigtail ureteric stent versus percutaneous nephrostomy: effects on stone transit and ureteric motility. Eur Urol 1997;31(1):24-29.

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