Urolithiasis Flashcards
Urolithiasis definition
= Calculi/uroliths (commonly known as stones) located anywhere along urinary tract
Causes of urolithiasis
- struvite
- calcium oxalate
- urate
- cysteine
- calcium phosphate
- xanthine
Where does urolithiasis normally occur in cats & dogs?
- lower urinary tract, i.e. bladder & urethra
What are struvite uroliths made from?
- Magnesium ammonium phosphate (MAP)
- supersaturation of urine by Map -> struvite urolith
What are struvite uroliths usually associated with in dogs? What about in cats?
- dogs: UTIs caused by urease producing bacteria
- cats: 90% are sterile – in contrast to dogs (infection-induced seen predominantly in cats > 10 yrs)
Prevalence of struvite uroliths
- Account for 40% of stones affecting lower urinary tract of dogs
– Females > males – likely due to increased tendency of female dogs to develop UTIs - Account for 50% of stones affecting lower urinary tract of cats
Risk factors for struvite uroliths in dogs
- Abnormal retention of urine; any condition predisposing to UTI – eg diabetes mellitus, hyperadrenocorticism
- Susceptible breeds – Miniature schnauzer, Shih Tzu, Bichon
Risk factors for struvite uroliths in cats
- Abnormal retention of urine
- Formation of concentrated urine – moisture content of food, water intake
- Urine-alkanising metabolites in diets
Calcium oxalate urolith prevalence
- Account for approx. 40% of stones in dogs and cats
Calcium oxalate urolith causes
❑ Aetiology poorly understood
❑ Hypercalciuria*, hyperoxaluria, hypocitraturia
❑ Hypercalciuria – increased intestinal reabsorption of calcium or reduced renal tubular reabsorption
- hypercalcaemia – renal tubular reabsorption mechanisms overwhelmed
Is recurrence of calcium oxalate uroliths common?
- yes
Calcium oxalate risk factors
❑ Acidifying diets
❑ Oral calcium supplements given outside of mealtimes
❑ Excessive dietary protein
❑ Formation of concentrated urine
What are urate uroliths made of?
- uric acid, sodium urate or ammonium urate
Cause of urate uroliths
- Impaired conversion of uric acid to allantoin
-> increased concentration of uric acid in serum andurine - Often associated with PSS – due to impaired hepatic metabolism of uric acid and ammonia
Breed predisposition for urate uroliths
- Dalmations and Black Russian terriers
- Associated with breeds predisposed to PSS eg Yorkshire Terriers
Urate urolith prevalence
- 5-8% of uroliths in dogs and cats
Urate urolith risk factors
❑ High Purine intake (glandular meat)
❑ Persistent aciduria in a predisposed animal
Cause of cysteine uroliths
❑ Cystinuria – inborn error of metabolism caused by defective tubular resorption of cysteine and other amino acids
❑ Not all cystinuric dogs develop cysteine uroliths – cystinuria is a predisposing factor
Cysteine urolith risk factors
❑ Genetic predisposition to cystinuria
❑ Acidic, concentrated urine
❑ Urine retention
Cysteine urolith signalment & breed predispositions
❑ Breeds with genetic mutations include Newfoundlands, Labradors, Australian cattle dogs, mastiffs and bulldogs
❑ Predominantly intact male dogs affected
Calcium phosphate urolith prevalence
❑ Pure Calcium Phosphate uroliths - less than 1% of all uroliths in dogs and cats
What are calcium phosphate uroliths often a minor component of?
- struvite and calcium oxalate uroliths
Xanthine urolith causes
❑ Impaired Xanthine oxidase activity leads to hyperxanthinaemia and xanthinuria
❑ Familial or congenital defect e.g. CKCS
❑ Allopurinol therapy can lead to acquired xanthinuria
Xanthine urolith risk factors
❑ Genetic predisposition
❑ Acid urine, highly concentrated urine
❑ Urine retention
❑ Allopurinol treatment
Urolithiasis: clinical signs
❑Lower urinary tract signs – dysuria, haematuria, pollakiuria
❑+/- signs of urinary obstruction
❑Urate – signs of PSS
Urolithiasis: diagnosis
- Urinalysis
- Imaging
- Ultrasound
Urinalysis for diagnosis
❑ Not as helpful as you might think
❑ pH is useful – partly clue to urolith type, but also for monitoring treatment/dietary management
❑ Need to rule out UTI – and if present, must 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 crystals are often absent when uroliths present
❑ If crystals present, may not represent urolith composition – eg struvite crystalluria often seen in dogs with calcium oxalate uroliths as urine is therapeutically alkalinised.
Radiography for diagnosis
- Radiopaque uroliths: Calcium Oxalate, Struvite, Calcium phosphate
- Radiolucent uroliths: Xanthine
- Variable: Urate, Cysteine
- Struvite: usually round/faceted, appear smooth
- Calcium Oxalate: more irregular
Ultrasound for diagnosis
❑ Acoustic shadowing
❑ Remember gravity when
deciding if mass or urolith
❑ Can be done conscious
❑ Will pick up radiolucent uroliths
When can you do urolith analysis?
- either post cystotomy, or if small uroliths are passed
Non-specific medical tx
❑ 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
Urate specific tx
❑ Allopurinol – Xanthine Oxidase inhibitor – for dissolution – takes at least 4-6 weeks, sometimes required long term
❑ Not effective if PSS – need to manage the shunt
Diets for dissolution (tx) (for each urolith)
- Calcium Oxalate: Not amenable to dissolution (dietary management is for prevention of recurrence)
- Struvite: Prescription struvite dissolution diet (acidifying)
- Urate: Low-purine, alkalinising diet (contraindicated if pregnant/lactating)
- Cysteine: Alkanising, lower methionine protein content
- Calcium phosphate: not amenable to dissolution
- Xanthine: low purine, alkalinising
Which uroliths would you treat surgically?
- Calcium Oxalate
- Calcium phosphate
- larger Struvite uroliths
Surgical tx
❑ Cystotomy, urethrotomy
❑ If blocked – try and push urolith(s) 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
Surgical tx - post op warnings to O
- warn owner of likely haematuria, need to monitor urine output, watch for dysuria
Surgical tx - peri- & post-op analgesia
- opioid
- NSAID
What else do you need to do post-surgery for struvite crystals?
- take urine sample for C & S (unless done recently)
Prevention of calcium oxalate uroliths
- High moisture alkalinising diet – but monitor for Struvite crystalluria
- Monitor – monthly urinalysis, aim for SG < 1.020 (dogs) & < 1.030 (cats) and pH >6.5
- Correct any hypercalcaemia
Prevention of struvite uroliths
- High moisture acidifying diet – but care re CaOx crystalluria
- Monitor urine pH & SG (as for CaOx but want pH < 7
- Ensure UTI fully resolved – repeat C & S at end of antibiotic course
Prevention of urate uroliths
- High moisture alkalinising diet
- Some dogs require long term Allopurinol
Prevention of cysteine uroliths
- High moisture alkalinising diet
- Dogs – consider castration, will reduce recurrence if have sex-linked genetic predisposition
Prevention of calcium phosphate uroliths
- High moisture diet; senior diets may be useful due to lower protein
Prevention of xanthine uroliths
- High moisture alkalinising diet
