12.7.4: Urolithiasis Flashcards
What are struvite crystals associated with in dogs?
- Usually associated with UTIs caused by urease-producing bacteria (this alters pH -> leads to crystals)
- More common in females than males due to increased UTIs in females
Risk factors
* Abnormal retention of urine (left inside / sedentary)
* Any condition predisposing to UTI e.g. diabetes mellitus, HAC
* Susceptible breeds: Mini Schnauzers, Shih Tzu, Bichon
What are struvite crystals associated with in cats?
- 90% sterile
- Accounts for 50% of lower urinary tract stones in cats
- Infection-induced are seen mostly in cats >10 y.o.
Risk factors
* Abnormal retention of urine
* Formation of concentrated urine (link to moisture content of food and water intake; if cat refuses to drink, urine will be even more concentrated than usual)
* Urine-alkalinising metabolites in diets
What are calcium oxalate crystals associated with in dogs and cats?
- Aetiology poorly understood
- Possibly due to hypercalciuria - increased intestinal or reduced renal tubular reabsorption of calcium
- Possibly due to hypercalcaemia - renal tubular reabsorption mechanisms overwhelmed
Risk factors
* Acidifying diets
* Oral calcium supplements given outside of meal times
* Excessive dietary protein
* Formation of concentrated urine
What are urate crystals asssociated with in dogs and cats?
- Composed of uric acid, sodium urate, or ammonium nitrate
- Impaired conversion of uric acid to allantoin -> increased concentration of uric acid in serum and urine
- About 5-8% uroliths
Risk factors
* High purine intake (glandular meat)
* Persistent aciduria ina predisposed animal
Which breeds are particularly predisposed to urate crystals?
- Dalmatians, Black Russian Terriers
- Often associated with portosystemic shunts (impaired hepatic metabolism of uric acid and ammonia) e.g. Yorkshire terries
What are cysteine crystals associated with?
- Cystinuria = inborn error of metabolism caused by defective tubular resorption of cysteine and other amino acids
- Not all cystinuric dogs develop cysteine uroliths, it is just a predisposing factors
- Predominantly intact male dogs affected
- Breeds with genetic mutations: Newfoundlands, Labs, Aussie cattle dogs, mastiffs, bulldogs
Risk factors
* Genetic predisposition to cystinuria
* Acidic, concentrated urine
* Urine retention
What are calcium oxalate crystals associated with?
What are xanthine crystals associated with?
Clinical signs of uroliths
- Lower urinary tract signs - dysuria, haematuria, pollakiuria
- ± signs of urinary obstruction
- If urate crystals -> signs of PSS
Diagnostics for uroliths
- Imaging is key - either ultrasound or radiography, possibly both
- Urinalysis helpful for pH, working out ongoing management, identification of any UTI; however crystals may not be present even if there is a urolith
Why might you not see crystals on urinalysis if there is a urolith?
- If a urolith has formed, minerals are more likely to be deposited on the surface of the urolith than to form new crystals
- This means crystals are often absent when there is a urolith present
- Even if there are crystals, they may not be of the same type as the urolith
You identify what you think is a mass on bladder ultrasound, but you are concerned it could possibly be a urolith. How will you check?
- Scan the dog in 2 different positions and see if the stone moves (urolith will move, mass won’t)
- You could also gentle ballot the abdomen to try and move the stone
Advantages of using ultrasound to detect uroliths compared to radiography?
- Can identify radiolucent uroliths
- Can be done conscious
What does radiographic appearance of uroliths tell you about them?
- Radiopaque uroliths: calcium oxalate, struvite, calcium phosphate
- Radiolucent uroliths: xanthine
- Variable: urate, cysteine
- Also consider shape
General medical treatment points for any urolith
- Analgesia (usually NSAID)
- Antibiotic e.g. co-amoxiclav PO if a concurrent UTI; C&S if prolonged course required
Medical treatment of urate crystals
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Which uroliths require surgery and how would you carry this out?
Use a partial thickness suture (e.g. Cushing pattern) in the bladder
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