Urolithiasis Flashcards
Urolithiasis pathogenesis
Disturbed equilibrium → precipitation of solutes into solid crystals that aggregate and grow in a protein matrix.
Mechanisms:
- Increased solute concentrations
- Decrease in excretion/function of natural crystallization inhibitors
- Urine pH changes
Suture material (nidus for mineralization)
Disorders that increase residual urine volume
struvite
What percentage of canine uroliths do struvite comprise?
40%
Pathogenesis of struvite crystals
Secondary to UTI.
Infections with urease-producing bacteria (e.g., Staphylococcus spp., Proteus spp.) increase urinary ammonium and pH, resulting in precipitation of struvite.
calcium oxalate
What percentage of canine uroliths do calcium oxalate comprise?
35%
(Calcium phosphate are another type but more rare, only comprising 1%.)
Pathogenesis of calcium oxalate crystals.
Idiopathic hypercalcinuria (Increased urinary calcium excretion despite normocalcemia)
up to <10% primary hyperparathyroidism or malignancy
Genetic predisposition
- Breeds: miniature schnauzer, yorkshire terrier, shih tzu, bichon frise, lhasa apso
cystine
What percentage of canine uroliths do cystine comprise?
6%
Pathogenesis of cystine crystals.
Cystinuria is a hereditary disorder caused by mutations in genes encoding subunits of a renal amino acid transporter.
causes an amino acid called cystine to build up in urine. Cystine can be excreted in urine and lead to the formation of bladder or kidney stones.
Cystinuria types.
Types I, II, III
Type I and II: mutations in genes encoding subunits of a renal amino acid transporter.
Newfoundland, australian cattle dog, labrador retriever, miniature pinscher
Type III: androgen dependent (70-80%) (most common)
Mastiff, scottish deerhound, english and french bulldog, rottweiler, basset hound, irish terrier
The most common form of cystinuria in dogs is
type III, androgen-dependent and thus sex-limited, with 70-90% of cystine uroliths submitted from intact males.
urate
What percentage of canine uroliths does urate comprise?
5%
Pathogenesis of urate crystals.
Decreased hepatic conversion of uric acid to allantoin → hyperuricosuria.
Causes:
Congenital portosystemic shunt
Hereditary hyperuricosuria (acidic urine):
Mutation in the uric acid transporter gene → decreased hepatic uptake and renal reabsorption of uric acid;
>90% dalmatians, >90% uroliths from
Neutered male dalmations. But can occur in other breeds too!
What type of crystals do dalmations get?
urate (acidic)
Name a rare purine urolith.
xanthine
(0.1% of submissions) caused by a deficiency in xanthine dehydrogenase (XDH), the enzyme that converts xanthine to uric acid.
Most (75%) canine xanthine uroliths are iatrogenic, caused by XDH inhibitor therapy (e.g., allopurinol) for management of urate stones or leishmaniasis, with the remainder attributed to hereditary defects.)
Signalment of typical urolith patient.
Middle-aged
>7 y: 60% CaOx, 35% struvite, 9% urate, 1% cystine
<7 y: 58% struvite, 26% CaOx, 25% urate, 5% cystine
Sex prevalence is equal but composition differs by sex.
Female: 74% struvite (UTI) compared to only 13% in males.
Male: 73% CaOx. Intact males: cystine
Certain dog breeds are predisposed to specific urolith types.
Clinical signs of urolithiasis. (8)
Lower urinary tract signs like Pollakiuria, periuria, stranguria
Hematuria
Urethral obstruction: unable to urinate
despite attempts
Partial obstruction: incontinence/dribbling
Urethral obstruction/ruptured bladder: systemic clinical signs like lethargy, anorexia, vomiting.
UTI: urine might have a foul smell
Congenital PSS: delayed growth, GI signs, abnormal mentation
Upper urinary tract disease: PU/PD, persistent hematuria without lower urinary tract signs.
Physical examination of a urolithiasis patient.
Most dogs with bladder and/or urethral uroliths have a normal physical examination.
But Large cystoliths may be palpable
Urethroliths may be palpable
Check Bladder size - if large could indicate (partial) obstruction.
Don’t forget Prostate palpation
The following diseases should be considered in dogs with lower urinary tract signs: (5)
bladder/urethral uroliths,
bacterial cystitis,
bladder/urethral neoplasia,
urethritis,
and in males, prostatic disease.
Rank based on signalment and PE. For example, 60% of females presenting with lower urinary tract signs have bacterial cystitis compared to only 25% of males.
Urinalysis in urolithiasis cases.
USG: lower urinary tract uroliths don’t affect it but dogs with uroliths may have concurrent diseases (CKD, PSS etc.)
pH: Acidic - urate, alkaline - struvite
Should not be the sole way of estimating the most likely type cause may not be accurate.
Proteinuria is common in urolithiasis.
Crystalluria: Presence/type of crystalluria do not accurately predict urolith presence/type. Struvite, amorphous phosphate, CaOx crystals may be normal.
Cystine, urate always abnormal.
Sample storage can cause crystals.
Hematuria is common.
Pyuria, bacteriuria
- In Struvite
- In ⅓ dalmatians with urate
Always Urine culture
What type of uroliths most commonly form in acidic urine and what type in alkali?
Acidic - urate
Alkaline - struvite
Imaging in urolithiasis cases in order to
identify, count, measure uroliths
+ To predict composition
Struvite: max 10 mm, ovoid/pyramidal shape
CaOx: rosette-shaped
+ signalment, risk factors
Greater than 90% of CaOx and struvite uroliths are estimated to be visible with plain radiography. In contrast, only 70-75% of urate and cystine uroliths are estimated to be detected because of their relatively poor radiopacity.
U/S in urolithiasis cases.
Ultrasonography can easily detect cystoliths, bladder wall abnormalities (masses, thickening, hematomas), and upper urinary tract uroliths; it is limited in its ability to detect urethroliths because of pelvic bone superimposition.
More sensitive than radiography for uroliths <1 mm
Uretheroliths difficult to detect tho.
Difficult to count them. Tendency to overestimate size.
Algorithm for selecting the best therapeutic options for dissolution or removal of cystoliths in dogs.
Treatment - struvite.
Struvite uroliths should first be medically dissolved (attempted) using a combination of a therapeutic dissolution diet and antimicrobial therapy to clear the concurrent UTI.
Success rates for medical dissolution of suspected struvite uroliths are 50-60%, with a median time to full dissolution of approximately 1 month.
Urolith removal if:
No dissolution by 4-6 weeks
Clinical signs fail to resolve within 2 weeks
Algorithm for when to suspect a struvite composition in a dog diagnosed with uroliths and how to implement a medical dissolution trial.
Treatment - CaOx.
Cannot be medically dissolved.
Prevention:
1. Diet
- Low oxalate, moderate calcium, optimal Ca:P, potassium citrate
- Potassium citrate supplementation
- Alkalinizer, crystallization inhibitor.
Indication: pH persistently <6.5, recurrent stones - Hydrochlorothiazide
- Reduces Ca excretion
- Recurrent stones
- Rule out hyperCa first
Recurrence rate as high as 50% in 2-3 y.
Treatment - cystine
Intact male dogs -> castration (androgen dependent cystinuria most common)
Medical dissolution
1. Diet: low animal protein, low Na, alkalinizing
- Potassium citrate alkalinizer supplement if urine remains acidic (target pH 7.5).
- Tiopronin med (cystine chelating agent) if castration and diet do not reduce cystinuria.
Treatment - urate
Medical dissolution
1. Low purine, alkalinizing diet
- Potassium citrate alkalinizer if urine remains acidic (target pH ≥7)
- Allopurinol with HHU (hereditary hyperuricosuria), persistent crystalluria despite diet and potassium citrate
+ low purine diet!
Full dissolution in 30-40% of cases in a median of 1 month.
PSS needs surgery
Urolithiasis in cats.
the most common feline uroliths being
struvite (magnesium ammonium phosphate [MAP]) and calcium oxalate (CaOx).
The remainder of stones that occur in cats include purine, cystine, calcium phosphate, compound, and mixed.
