Urolithiasis

Question 1

How do urinary stone develop?

Answer 1

microcrystals —> macrocrystals —> stones

Question 2

What are the 2 most common uroliths in cats and dogs?

Answer 2

struvite and calcium oxalate

(both radiopaque)

Question 3

What is the nidus of a urolith?

Answer 3

area of urolith initiation, typically a foreign material that causes growth

Question 4

What is the composition and structure of struvite?

Answer 4

magnesium ammonium phosphate hexahydrate

round/angular, large smooth stones that are radiopaque

Question 5

What is the cause of struvite formation in dogs and cats?

Answer 5

DOGS - bacteria, like Staph and Proteus, that produce urease

CATS - sterile struvite formation

Question 6

In what urine does struvite form? What gender is predisposed?

Answer 6

alkaline

female - more likely to get UTIs

Question 7

What 3 breeds are predisposed to forming struvite stones?

Answer 7

1. Miniature Schnauzer
2. Bichon
3. Cocker Spaniel

Question 8

What is the structure of calcium oxalate stones? What causes their formation?

Answer 8

irregular, spiked stones that are radiopaque

urine supersaturation from hypercalciuria, acidity, or concentrated urine

Question 9

How do urate stones appear on radiographs? In what urine do they develop?

Answer 9

radiolucent - become radiopaque with increasing size

acidic

Question 10

What is the most common cause of urate stone formation? In what animals is this an inherited disorder? Why does this occur?

Answer 10

hepatic portovascular anomalies - liver unable to turn ammonia into urea

Dalmations and English Bulldogs with alterations of SLC2A9 urate transported - uric acid is unable to become allantoin

Question 11

How do cystine stones appear on radiographs? What are 2 causes of their formation?

Answer 11

radiolucent

1. inherited defect in renal tubular transporters of cystine seen in young/middle-aged male Dachshunds, Bassets, English Bulldogs, Irish and Yorkshire Terriers, Mastiffs, Chihuahuas, Tibetan Spaniels
2. acidic pH

Question 12

What are 2 causes of xanthin stone formation?

Answer 12

1. hereditary
2. allopurinol use (common treatment for genetic urinary stoner)

Question 13

What is the main cause of silicate stone formation? 3 examples?

Answer 13

consumption of specific dietary ingredients

1. substantial quantities of corn gluten feed or grain hull
2. water in volcanic areas
3. inert ingredient in some tablet mediccations

Question 14

Urinary stones:

Answer 14

Question 15

Why is urinary stone treatment so important?

Answer 15

• causes UTIs by compromising host defenses
• causes dysuria
• can cause partial or total urinary obstruction
• polyp formation with chronic uroepithelial irritation

Question 16

How is the likelihood of the type of urinary stone determined?

Answer 16

• breed
• pH
• imaging
• presence of UTI

Question 17

What medical, nutritional, and monitoring considerations are used for struvite stones?

Answer 17

penicillins throughout most, if not all, of dissolution times (2-3 months)

struvite dissolution diets (Hills s/d, c/d, multicare) - wet > dry

X-ray every 4-6 weeks

Question 18

In what 4 ways can recurrence of struvite stones be minimized?

Answer 18

1. identify and eradicate structural and functional risk factors with urine cultures
2. penicillins are usually effective against urease-forming bacteria, confirm with culture and sensitivity
3. feed diets lower in protein, phorphorus, and magnesium and that promote the formation of acidic urine
4. periodic urine cultures

Question 19

What is the main strategy of feline struvite dissolution? What medication and monitoring is recommended?

Answer 19

nutritional (UTIs don’t form struvite in cats) - Hills c/d, s/d, multicare

medication to decrease urinary pain

X-ray in 2-3 weeks

Question 20

What urinary stones are unable to be dissolved?

Answer 20

calcium oxalate —> 50% of dogs will have reformation!

Question 21

What 3 medical treatments should be considered for calcium oxalate stones?

Answer 21

1. additional water to reduce urine specific gravity below 1.020 (decrease supersaturation!)
2. potassium citrate if urine pH is consistently less than 6.5
3. hydrochlorothiazide diuretic considered if not hypercalcemic

Question 22

A 7 m/o FI Yorkshire Terrier presents with pollakiuria and hematuira. PE is unremarkable.

• Biochemistry = hypoglycemia, hypoalbuminemia, hypocholesterolemia, low BUN
• UA = USG 1.010, ammonium biurate crystals, inactive

What is occuring?

Answer 22

LUT signs indicative of inflammation or stones (inactive = no UTI)

biochem indicative of livery dysfunction/failure (+ ammonium biurate crystals)

likely a congenital portosystemic shunt, which can be confirmed with AUS and bile acids

TX: surgery, allopurinol blocks uric acid synthesis from xanthin (can cause xanthine stones!), decreased purine diet

Question 23

A dog presents for hematuria and dysuria persisting despite antibiotic treatment. UA shows alkaline urine, struvite crystalluria, and G- rods. Abdominal radiographs show radiopaque uroliths. Which urolith type and bacteria is most likely?

a. struvite, Proteus
b. struvite, E. coli
c. calcium oxalate, E. coli
d. ammonium urate, Klebsiella

Answer 23

A

Question 24

Which of the following is most important for preventing recurrence of struvite uroliths in dogs?

a. feeding therapeutic diets (Hills c/d)
b. controlling urinary tract infections
c. taking radiographs every 6 months
d. stimulating diuresis

Answer 24

B

Question 25

What is urohydropulsion? What sizes of uroliths allows for this in dogs and cats?

Answer 25

filling the bladder with water, holding them upright or on a tilted table to move the stones near the urethral opening, and push on bladder

• DOGS = < 4 mm in females and < 3 mm in males greater than 7 kgs
• CATS = < 2 mm in females and < 1 mm in males (PU only)