Urolithiasis Flashcards
Describe the history and presenting clinical signs in a dog with bladder stones
- Variable - asymptomatic to complete urinary tract obstruction
- Pollakiuria
- Dysuria / urinary tenesmus
- Discomfort / vocalisation on urination
- Haematuria
Describe the physical exam findings in a dog with bladder stones
May feel stones in bladder
May be abdominal pain (usually not)
How are canine bladder stones diagnosed?
Imaging
Describe the use of imaging for bladder stones
Imaging tells you the presence of uroliths and location, number, size, shape, and density
The preferred contrast technique for uroliths is double contrast
Urates are found normally in which breed?
Dalmations
Crystal type may suggest the urolith type, but when is this not true?
- If diet has changed, may be different
- UTI (development or cure) can lead to different crystal types
How is USG related to bladder stones?
A high urine specific gravity suggests an increase in concentration of urolithic precursors.
How is pH related to bladder stones?
Ph can suggest which urolith is present - oxalate, purines, and cystine uroliths form typically in urine with a pH less than 7.0, whereas struvite calculi form typically in urine with a pH greater than 7.0
How is culture related to bladder stones?
Culture indicated because urinary tract infections may occur secondarily in patients with urolithiasis or may induce urolith formation
Which crystal has a coffin shaped appearance?
Struvite
Which crystal has a pyramidal shape?
Calcium oxalate dihydrate
Are blood tests useful in cases of bladder stones?
Yes
- Underlying diseases e.g. hypercalcaemia
- Effects of obstruction
- Liver function if urate stones found
Why is analysis of the urolith performed?
Essential to prevent recurrence!
If uroliths recur, resubmit!
Describe the composition of uroliths
- A urolith is composed primarily of 1 or more minerals in combination with small quantities of organic matrix.
- Layers of stone are: the nidus, stone, shell, and surface crystals
Why is the nidus of the stone important?
The nidus is the area of obvious initiation of stone growth. – not necessarily right in the middle.
Nidus needs to be the focus of prevention
Describe the advantages and disadvantages of medical dissolution of stones
Advantage - Less invasive
Disadvantages
- Owner compliance with diet
- Repeated radiographs, urinalysis and culture
- Some stones do not dissolve
- May block urethra
Which stones dissolve, and which dont?
Do = Struvite, urate, cystine
Don’t = Oxalate, silicate, phosphate
List the indications for calculi removal
Obstruction
Increase in size or number of calculi
Persistent clinical signs
Lack of response to therapy
Voiding urohydropropulsion can be used to remove uroliths of what size?
1 to 3 mm in male dogs
up to 10 mm in female dogs
Does struvite form in acidic or alkaline urine?
Alkaline
What can predispose the formation of struvite crystals?
A urinary tract infection needs to occur for struvite to form
Do struvite crystals form in the lower or upper urinary tract?
LUT (95%) > UUT (5%)
What other elements must be present in the urine fot struvite to form?
urine must be oversaturated with magnesium, ammonium, and phosphate ions
How are struvite crystals treated/managed?
- Treat the UTI
- Feed a diet with reduced protein, phosphorus and magnesium that promotes formation of acidic urine (i.e. pH <6.5)
- High moisture food is preferred
- Give appropriate antimicrobial agent during the entire time of medical dissolution
How is struvite dissolution monitored?
Urinalysis and imaging 4-6 weeks
- Expect USG <1.020 and 20% reduction in stone size
- Repeat every 4-6 weeks
- Continue for 2-4 weeks after radiographic cure
What are some possible reasons that struvite doesn’t dissolved?
The UTI isn’t controlled
Core of oxalate
How can you prevent struvite formation?
- Prevent the urinary tract infection from recurring
- Treat bacterial infections as they arise
- Dietary modification does not prevent infection-induced struvite uroliths
- And many breeds are also predisposed to calcium oxalate!
Calcium oxalate crystals form in acidic or alkaline urine?
Neutral-acidic
What condition predisposed to calcium oxalate crystals?
Hypercalcaemia
Describe the predispositions for calcium oxalate formation
Males (70%) > females (30%)
Certain breeds
Age - more common in older dogs
How are calcium oxalate crystals treated?
- Medical protocols that promote dissolution of calcium oxalate uroliths are not available
- Uroliths must be removed physically
- Calcium oxalate uroliths are recurrent!
How can calcium oxalate crystals be prevented?
- Rule out: Hypercalcaemia, Metabolic acidosis and Vitamin D excess
- Increase urine volume:
- Increase voiding frequency
- High-moisture (>75% water) foods
- Aim for USG < 1.020
Do urates form in acidic or alkaline urine?
Acidic
Describe the appearance of urates
Radiolucent, smooth, round or oval
When are urates a normal finding?
They are the end product of purine catabolism in humans, higher primates, and Dalmatian dogs.
Urate stones in dogs form due two which two possible distinct situations?
Inherited alteration of the urate transporter
PSS – portosystemic shunt
Describe the predispositions for urate formation
- Breeds: Dalmatians, English Bulldogs
- Dogs that get PSS e.g. Yorkshire Terrier, Miniature Schnauzer
- Sex: Males (85%) > females
- UTIs (urease-producing bacteria)
- High protein diet
Which tests should you run to confirm urates?
Serum bile acid concentrations
Genetic Hyperuricosuria testing (SLC2A9 gene)
How should urates be managed in dogs without liver disease?
Dissolution of urate uroliths usually within 4 weeks
Suitable diet
Alkalinise urine if necessary with potassium citrate or sodium bicarbonate
Describe a suitable diet for a dog with urate crystals
- Low in protein
- Low in purines
- Produce alkaline urine
Examples of dissolution diet = Hills u/d
How can recurrence of urates be prevented?
Continue feeding the low purine diet. Check:
- urine pH (>7)
- USG (<1.020)
- BUN (low)
- Sediment (no crystals)
Drugs-
- Consider allopurinol
- Consider potassium citrate if urine pH is consistently less than 6.6.
Why do cystine crystals form?
Inherited disorder of renal tubular transport
Describe the appearance of cystine
Radiolucent, smooth, small.
Crystals flat, colourless, hexagonal
Which patients are predisposed to cystine crystals
Male (90%) > female
Dachshunds, others
Several genetic mutations have been identified - some are sex linked/androgen responsive
How are cystine crystals treated?
Encourage water intake
Suitable dissolution diet- Hills u/d, RCW Urinary U/C
Neutering for cystine uroliths?
What are mixed composition stones?
Between 5% and 15% of uroliths may be mixed or compound stones
Refers to a situation in which more than 1 mineral is present within the stone, either mixed within all layers or different parts of the stone are composed of different minerals
Which uroliths that can be medically dissolved?
Struvite
Urates
Cystine
Which urolith is most commonly seen in females?
Struvite
Which intervention is important in ALL uroliths?
Increase water intake
Which uroliths that are usually radiopaque, and which are radiolucent?
Radiopaque = oxalate, struvite
Radiolucent = urate, cystine
