Urolithiasis

Question 1

Urolithiasis definition

Answer 1

= Calculi/uroliths (commonly known as stones) located anywhere along urinary tract

Question 2

Causes of urolithiasis

Answer 2

• struvite
• calcium oxalate
• urate
• cysteine
• calcium phosphate
• xanthine

Question 3

Where does urolithiasis normally occur in cats & dogs?

Answer 3

• lower urinary tract, i.e. bladder & urethra

Question 4

What are struvite uroliths made from?

Answer 4

• Magnesium ammonium phosphate (MAP)
• supersaturation of urine by Map -> struvite urolith

Question 5

What are struvite uroliths usually associated with in dogs? What about in cats?

Answer 5

• dogs: UTIs caused by urease producing bacteria
• cats: 90% are sterile – in contrast to dogs (infection-induced seen predominantly in cats > 10 yrs)

Question 6

Prevalence of struvite uroliths

Answer 6

• 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

Question 7

Risk factors for struvite uroliths in dogs

Answer 7

• Abnormal retention of urine; any condition predisposing to UTI – eg diabetes mellitus, hyperadrenocorticism
• Susceptible breeds – Miniature schnauzer, Shih Tzu, Bichon

Question 8

Risk factors for struvite uroliths in cats

Answer 8

• Abnormal retention of urine
• Formation of concentrated urine – moisture content of food, water intake
• Urine-alkanising metabolites in diets

Question 9

Calcium oxalate urolith prevalence

Answer 9

• Account for approx. 40% of stones in dogs and cats

Question 10

Calcium oxalate urolith causes

Answer 10

❑ Aetiology poorly understood
❑ Hypercalciuria*, hyperoxaluria, hypocitraturia
❑ Hypercalciuria – increased intestinal reabsorption of calcium or reduced renal tubular reabsorption
- hypercalcaemia – renal tubular reabsorption mechanisms overwhelmed

Question 11

Is recurrence of calcium oxalate uroliths common?

Answer 11

• yes

Question 12

Calcium oxalate risk factors

Answer 12

❑ Acidifying diets
❑ Oral calcium supplements given outside of mealtimes
❑ Excessive dietary protein
❑ Formation of concentrated urine

Question 13

What are urate uroliths made of?

Answer 13

• uric acid, sodium urate or ammonium urate

Question 14

Cause of urate uroliths

Answer 14

• 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

Question 15

Breed predisposition for urate uroliths

Answer 15

• Dalmations and Black Russian terriers
• Associated with breeds predisposed to PSS eg Yorkshire Terriers

Question 16

Urate urolith prevalence

Answer 16

• 5-8% of uroliths in dogs and cats

Question 17

Urate urolith risk factors

Answer 17

❑ High Purine intake (glandular meat)
❑ Persistent aciduria in a predisposed animal

Question 18

Cause of cysteine uroliths

Answer 18

❑ 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

Question 19

Cysteine urolith risk factors

Answer 19

❑ Genetic predisposition to cystinuria
❑ Acidic, concentrated urine
❑ Urine retention

Question 20

Cysteine urolith signalment & breed predispositions

Answer 20

❑ Breeds with genetic mutations include Newfoundlands, Labradors, Australian cattle dogs, mastiffs and bulldogs
❑ Predominantly intact male dogs affected

Question 21

Calcium phosphate urolith prevalence

Answer 21

❑ Pure Calcium Phosphate uroliths - less than 1% of all uroliths in dogs and cats

Question 22

What are calcium phosphate uroliths often a minor component of?

Answer 22

• struvite and calcium oxalate uroliths

Question 23

Xanthine urolith causes

Answer 23

❑ Impaired Xanthine oxidase activity leads to hyperxanthinaemia and xanthinuria
❑ Familial or congenital defect e.g. CKCS
❑ Allopurinol therapy can lead to acquired xanthinuria

Question 24

Xanthine urolith risk factors

Answer 24

❑ Genetic predisposition
❑ Acid urine, highly concentrated urine
❑ Urine retention
❑ Allopurinol treatment

Question 25

Urolithiasis: clinical signs

Answer 25

❑Lower urinary tract signs – dysuria, haematuria, pollakiuria ❑+/- signs of urinary obstruction ❑Urate – signs of PSS

Question 26

Urolithiasis: diagnosis

Answer 26

- Urinalysis - Imaging - Ultrasound

Question 27

Urinalysis for diagnosis

Answer 27

❑ 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.

Question 28

Radiography for diagnosis

Answer 28

- Radiopaque uroliths: Calcium Oxalate, Struvite, Calcium phosphate - Radiolucent uroliths: Xanthine - Variable: Urate, Cysteine - Struvite: usually round/faceted, appear smooth - Calcium Oxalate: more irregular

Question 29

Ultrasound for diagnosis

Answer 29

❑ Acoustic shadowing ❑ Remember gravity when deciding if mass or urolith ❑ Can be done conscious ❑ Will pick up radiolucent uroliths

Question 30

When can you do urolith analysis?

Answer 30

- either post cystotomy, or if small uroliths are passed

Question 31

Non-specific medical tx

Answer 31

❑ 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

Question 32

Urate specific tx

Answer 32

❑ 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

Question 33

Diets for dissolution (tx) (for each urolith)

Answer 33

- 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

Question 34

Which uroliths would you treat surgically?

Answer 34

- Calcium Oxalate - Calcium phosphate - larger Struvite uroliths

Question 35

Surgical tx

Answer 35

❑ 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

Question 36

Surgical tx - post op warnings to O

Answer 36

- warn owner of likely haematuria, need to monitor urine output, watch for dysuria

Question 37

Surgical tx - peri- & post-op analgesia

Answer 37

- opioid - NSAID

Question 38

What else do you need to do post-surgery for struvite crystals?

Answer 38

- take urine sample for C & S (unless done recently)

Question 39

Prevention of calcium oxalate uroliths

Answer 39

- 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

Question 40

Prevention of struvite uroliths

Answer 40

- 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

Question 41

Prevention of urate uroliths

Answer 41

- High moisture alkalinising diet - Some dogs require long term Allopurinol

Question 42

Prevention of cysteine uroliths

Answer 42

- High moisture alkalinising diet - Dogs – consider castration, will reduce recurrence if have sex-linked genetic predisposition

Question 43

Prevention of calcium phosphate uroliths

Answer 43

- High moisture diet; senior diets may be useful due to lower protein

Question 44

Prevention of xanthine uroliths

Answer 44

- High moisture alkalinising diet