Urolithiasis

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Lucy The 3rd

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Definition of urolithiasis
Calculi/uroliths (commonly known as stones) located anywhere along urinary tract in dogs and cats - normally lower urinary tract i.e. bladder and urethra.
Struvite risk factors
Magnesium ammonium phosphate (MAP).
Supersaturation of urine by MAP leads to the formation of struvite urolith.
Formation of uroliths in dogs
Usually associated with UTIs caused by urease producing bacteria.
Account for 40% of stones affecting lower urinary tract of dogs.
Females get them more than males - likely due to increased tendency of female dogs to develop UTIs.
Risk factors for uroliths in dogs
Abnormal retention of urine; any condition predisposing to UTI - e.g. diabetes mellitus, hyperadrenocorticism.
Susceptible breeds - miniature schnauzer, Shih Tzu, Bichon.
Formation of uroliths in cats
90% are sterile - in contrast to dogs (infection-induced seen predominantly in cats > 10 years).
Account for 50% of stones affecting lower urinary tract of cats.
Risk factors for uroliths in cats
Abnormal retention of urine.
Formation of concentrated urine - moisture content of food, water intake.
Urine-alkalising metabolites in diets.
Formation of calcium oxalate crystals
Aetiology poorly understood.
Hypercalciuria, hyperoxaluria, hypocitraturia.
Hypercalciuria - increased intestinal reabsorption of calcium or reduced renal tubular reabsorption.
Recurrence is common, account fr approximately 40% of stones in dogs and cats.
Risk factors for calcium oxalate crystals
Acidifying diets.
Oral calcium supplements given outside of mealtimes.
Excessive dietary protein.
Formation of concentrated urine.
Formation of urate crystals.
Composed of uric acid, sodium urate or ammonium urate.
Impaired conversion of uric acid to allantoin leading to increased concentration of uric acid in serum and urine.
5-8% of uroliths in dogs and cats.
Dalmations and Black Russian terriers have breed disposition.
Often associated with PSS - due to impaired hepatic metabolsim of uric acid and ammonia - so urate uroliths also associated with breeds predisposed to PSS e.g. Yorkshire terriers.
Risk factors for the formation of urate crystals
High purine intake (glandular meat).
Persistent aciduria in a predisposed animal.
Formation of Cysteine crystals
Cystinuria - inborn error of metabolism caused by defective tubular resorption of cysteine and other amino acids.
Breeds with genetic mutations include Newfoundlands, Labradors, Australian cattle dogs, mastiffs, and bulldogs.
Not all cystinuric dogs develop cysteine uroliths - cystinuria is a predisposing factor.
Predominantly intact male dogs affected.
Risk factors for the formation of Cysteine crystals
Genetic predisposition to cystinuria.
Acidic, concentrated urine.
Urine retention.
Formation of Calcium phosphate crystals
Pure calcium Phosphate uroliths - less than 1% of all uroliths in dogs and cats.
Often a minor component of Struvite and Calcium Oxalate uroliths.
Risk factors for the formation of Calcium phosphate crystals
Excessive dietary calcium, primary hyperparathyroidism.
UTI - with urease producing bacteria.
Formation of Xanthine crystals
Impaired Xanthine oxidase activity leads to hyperxanthinaemia and xanthinuria.
Familial or congenital defect e.g. CKCS.
Allopurinal therapy can leads to acquired xanthinuria.
Risk factors for the formation of Xanthine crystals
Generic predisposition
Acid urine, highly concentrated urine.
Urine retention.
Allopurinal treatment.
Clinical signs of uroliths
Lower urinary tract signs - dysuria, haematuria, pollakiuria.
+/- signs of urinary obstruction.
Urate - signs of PSS.
Diagnosis of urolithiasis - urinalysis
pH is useful - partly clue to urolith type, but also for monitoring treatment/dietary management.
Need to rule out UTI - and if present, mus treat especially if struvite uroliths.
Crystals can be misleading - once a urolith has formed, minerals are more likely to be deposited on the surface of the urolith than to form new crystals, so crystal are often absent when uroliths present.
Diagnosis of urolithiasis - radiograph imaging
Radiopaque uroliths - calcium oxalate, Struvite, Calcium phosphate.
Radiolucent uroliths - Xanthine
Variable - Urate, Cysteine.
Diagnosis of urolithiasis - ultrasound diagnosis
Acoustic shadowing.
Remember gravity when deciding if mass or urolith.
Can be done conscious.
Will pick up radiolucent uroliths.
Treatment of urolithiasis in general
Analgesia - usually NSAID
Antibiotic if concurrent UTI (e.g. with Struvite) - culture and sensitivity as will usually need prolonged course if uroliths present.
Lithotripsy - only one place in the UK currently, owners may ask about it.
Treatment of uroliths - urate
Allopurinal - Xanthine Oxidase inhibitor - for dissolution - takes at 4-6 weeks, sometimes required long term.
Not effective if PSS - need to manage the shunt.
Treatment of uroliths - calcium oxalate
Not amenable to dissolution (dietary management is for the prevention of recurrence).
Treatment of uroliths - struvite
Prescription struvite dissolution diet (acidifying).
Treatment of uroliths - urate
Low-purine, alkalinising diet (contraindicated if pregnant/lactating).
Treatment of uroliths - Cysteine
Alkalinising, lower methionine protein content.
Treatment of uroliths - Calcium phosphate
Not amenable to dissolution.
Treatment of uroliths - Xanthine
Low purine, alkalinising.
Treatment of uroliths - surgery
Calcium Oxalate, Calcium phosphate, and larger Struvite Uroliths.
Cystotomy, urethrotomy
If blocked - try and push uroliths back into bladder by retrograde urohydropulsion.
Cystotomy - rarely an emergency - remember lower ASA risk if planned not emergency, can ensure adequate personnel available, do in morning so time to recover and usually home same day.
Management of urolithiasis - calcium oxalate
High moisture alkalinising diet - but monitor for Struvite crystalluria.
Monitor - monthly urinalysis, aim for SG < 1.020 (dogs) & (cats) and pH >6.5.
Correct any hypercalcaemia.
Management of urolithiasis - Struvite
High moisture acidifying diet - but care for reoccurrence of CaOx crystalluria.
Monitor urine pH & SG (as for CaOx but want pH <7).
Ensure UTI if fully resolved - repeat C&S at end of antibiotic course.
Management of urolithiasis - Urate
High moisture alkalinising diet.
Some dogs require long term Allopurinol.
Management of urolithiasis - Cysteine
High moisture alkalinising diet.
Dogs - consider castration, will reduce recurrence if have sex-linked genetic predisposition.
Management of urolithiasis - Calcium Phosphate
High moisture diet, senior diets may be useful due to lower protein.
Management of urolithiasis - Xanthine
High moisture alkalinising diet.