Urolithiasis in small animals

Question 1

uroliths - define

Answer 1

Urinary Calculi - Stones

macroscopic

Question 2

Crystals

Answer 2

microscopic
do not cause clinical signs
can have crystals without uroliths and uroliths without crystals
may be representative of urolith type, but are not always

Question 3

How are uroliths formed?

Answer 3

Crystals form when urine is supersaturated
conc of solute required to start the process (nucleation) is generally higher than that required for growth
if conc of solute can be reduced sufficiently then crystals can dissolve

Question 4

Nephroliths and Ureteroliths - HX

Answer 4

Asymptomatic
Pyelonephritis
Renal failure (if bilateral obstruction or infection)
Renal colic?

Question 5

Nephroliths and Ureteroliths - PE

Answer 5

Often normal

Hydronephrosis/ irregular kidneys

Question 6

Cystoliths - clinical signs

Answer 6

Dysuria, pollakiuria, haematuria
Inappropriate urination
generally not palpable

Question 7

Urethroliths - clinical signs

Answer 7

Abdominal discomfort
Poor or no urine stream
Licking of genital area
Obstruction and post renal azotaemia
Enlarged painful bladder, urethroliths may be palpable per rectum or at base of os penis

Question 8

diagnosis

Answer 8

Hx + PE
plain radiography
contrast radiography
ultrasound

Question 9

predicting urolith type

Answer 9

Signalment - Sex, Breed, Age
Radiopaque or radiolucent
Urine pH
History of a particular stone type 
UTI associated with struvite
Disease associations

Question 10

renal + ureteral stones - treatment

Answer 10

Surgical removal - Urinary bypass
Dietary dissolution - must be non-obstructed
calcium oxalate – not amenable to dissolution
Benign neglect

Question 11

treatments - bladder

Answer 11

Medical dissolution
Voiding urohydropropulsion
Surgery - Cystotomy

Question 12

treatments - urethra

Answer 12

Retrograde flush into bladder

Surgery - Urethrotomy, Urethrostom

Question 13

medical management - indications

Answer 13

Should be attempted prior to surgery if appropriate
No obstruction
No contra-indications to dietary therapy
Urolith composition is amenable to dissolution
Struvite, cystine and urate generally amenable

Question 14

medical management

Answer 14

Dec conc in urine by incr water intake
Decr quantity of calculogenic crystalloids by diet or drug therapy
Incr solubility of salts by changing pH of the urine with diet
Treat any predisposing cause

Question 15

Urohydropropulsion

Answer 15

Fill bladder with saline
Position so urethra vertical
Agitate
Allow stones to settle
Initiate voiding
Continue pressure tokeep brisk urine flow
3 days antibiotics

Question 16

struvite

Answer 16

aka magnesium ammonium phosphate, triple phosphate
Many breeds
Most dogs have concurrent UTI - Most female, Urease producing bacteria, Staph, Proteus, Cleave urea - ammonium + bicarbonate
Alkaline urine pH
Usually sterile in cats

Question 17

struvite - treatment

Answer 17

Treat UTI for 3-4 weeks after radiographic resolution
Reduce urinary magnesium, ammonium, phosphate
Maintain pH <1.015, neg sediment, negative culture
If no improvement after 60 days consider persistent UTI, different type of urolith, owners feeding other foods

Question 18

struvite - prevention

Answer 18

Hills and Royal Canin diets
not recommended for dogs unless sterile stones were present
Monitor for recurrence of UTIs
Diets for struvite prevention may lead to calcium oxalate stone formation

Question 19

Calcium oxalate

Answer 19

incr incidence in cats
breed dispositions
More males than females affected
Older animals
Upper urinary tract
stones v.radiopaque

Question 20

Calcium oxalate - treatment

Answer 20

Surgery
Urohydropropulsion 
Medical dissolution not possible
‘Benign neglect’
60% recurrence in 3 years

Question 21

Calcium oxalate - prevention

Answer 21

Incr water intake
Sodium supplementation? - Induces diuresis
Neutral/marginally alkaline urine pH, Solubility of calcium oxalate is NOT pH dependent, Acidifying diets promote calcium excretion

Question 22

ammonium urate

Answer 22

8% canine stones
Dalmatians - decr conversion of uric acid to allantoin, Defective transport uric acid into hepatocytes & out of the urine
Hepatic dysfunction - Porto-systemic shunt, Incr excretion of ammonia and urea
E. Bulldogs, other breeds

Question 23

ammonium urate - treatment

Answer 23

Treat underlying liver disease, correct PSS
In other cases, dissolution is possible
Treat any UTI

Question 24

ammonium urate - prevention

Answer 24

Reduce purines, neutral to alkaline pH - Hills u/d
Allopurinol - competitively inhibits x.oxidase, reducing uric acid this can result in xanthine stones if protein not restricted

Question 25

cystine

Answer 25

About 3% of canine stones from the UK
Specific breed predispositions - daschund, staphy
Usually males
Renal tubular defect resulting in excess urine cystine which is poorly soluble
Stones are typically diagnosed in middle aged dogs, despite this being a congenital problem
Radiolucent
Medical dissolution effective but very expensive
Castration responsive in some dogs

Question 26

calcium phosphate

Answer 26

may be associated with primary hyperparathyroidism; may also occur as part of a mixed urolith or due to mineralization of a blood clot

Question 27

calcium carbonate

Answer 27

Most common stone type in rabbits and horses

High [Ca2+] in urine

Question 28

silica

Answer 28

GSDs predisposed, but rare; associated with poor diets

Question 29

indications for surgical treatment

Answer 29

Urinary tract obstruction
Unknown or unpredictable urolith composition
Failure of medical treatment
Presence of other urinary tract abnormalities
Immature dogs
Owner preference
Cost

Question 30

surgical options

Answer 30

Nephrotomy (nephrolithotomy)
Pyelotomy (pyelolithotomy)
Ureterotomy (ureterolithotomy)
Cystotomy (cystolithotomy)
Urethrotomy (urethrolithotomy)
Urethrostomy

Question 31

surgical considerations

Answer 31

Stabilise hyperkalaemic and severely azotaemic animals pre surgery
Ensure the number and location of the calculi are known immediately before surgery
Place an indwelling urinary catheter (with extension set) and empty bladder
Check all calculi / fragments of calculi are removed at end of surgery
Submit calculi for quantitative analysis