Urolithiasis in small animals Flashcards
uroliths - define
Urinary Calculi - Stones
macroscopic
Crystals
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
How are uroliths formed?
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
Nephroliths and Ureteroliths - HX
Asymptomatic
Pyelonephritis
Renal failure (if bilateral obstruction or infection)
Renal colic?
Nephroliths and Ureteroliths - PE
Often normal
Hydronephrosis/ irregular kidneys
Cystoliths - clinical signs
Dysuria, pollakiuria, haematuria
Inappropriate urination
generally not palpable
Urethroliths - clinical signs
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
diagnosis
Hx + PE
plain radiography
contrast radiography
ultrasound
predicting urolith type
Signalment - Sex, Breed, Age Radiopaque or radiolucent Urine pH History of a particular stone type UTI associated with struvite Disease associations
renal + ureteral stones - treatment
Surgical removal - Urinary bypass
Dietary dissolution - must be non-obstructed
calcium oxalate – not amenable to dissolution
Benign neglect
treatments - bladder
Medical dissolution
Voiding urohydropropulsion
Surgery - Cystotomy
treatments - urethra
Retrograde flush into bladder
Surgery - Urethrotomy, Urethrostom
medical management - indications
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
medical management
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
Urohydropropulsion
Fill bladder with saline Position so urethra vertical Agitate Allow stones to settle Initiate voiding Continue pressure tokeep brisk urine flow 3 days antibiotics
struvite
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
struvite - treatment
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
struvite - prevention
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
Calcium oxalate
incr incidence in cats breed dispositions More males than females affected Older animals Upper urinary tract stones v.radiopaque
Calcium oxalate - treatment
Surgery Urohydropropulsion Medical dissolution not possible ‘Benign neglect’ 60% recurrence in 3 years
Calcium oxalate - prevention
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
ammonium urate
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
ammonium urate - treatment
Treat underlying liver disease, correct PSS
In other cases, dissolution is possible
Treat any UTI
ammonium urate - prevention
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
cystine
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
calcium phosphate
may be associated with primary hyperparathyroidism; may also occur as part of a mixed urolith or due to mineralization of a blood clot
calcium carbonate
Most common stone type in rabbits and horses
High [Ca2+] in urine
silica
GSDs predisposed, but rare; associated with poor diets
indications for surgical treatment
Urinary tract obstruction
Unknown or unpredictable urolith composition
Failure of medical treatment
Presence of other urinary tract abnormalities
Immature dogs
Owner preference
Cost
surgical options
Nephrotomy (nephrolithotomy) Pyelotomy (pyelolithotomy) Ureterotomy (ureterolithotomy) Cystotomy (cystolithotomy) Urethrotomy (urethrolithotomy) Urethrostomy
surgical considerations
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
