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.
Urolith analysis.
Urolith analysis is vital for delineating pathogenesis, clinical management, and prognosis.
Conditions contributing to urolith formation in an individual dog can change over time, depending on environment, diet, and comorbidities. For this reason, it is essential to submit uroliths for analysis with each recurrence, rather than assume the composition based on previous urolithiasis events.
Similarly, if uroliths are removed from the upper and lower urinary tracts, uroliths from both locations should be submitted.
Should be dry when sent.
Most uroliths contain a predominant mineral type (>70%).
A urolith is referred to as “mixed” if
no single mineral comprises greater than 70% of a layer or “compound” if 1 portion of the urolith comprises at least 70% of 1 mineral type and 1 or more other layers are primarily (>70%) of a different mineral.
Factors that initiate urolith formation (nidus/core) may be different from those that allow urolith growth and subsequent layers (stone, shell, surface crystals). Therefore, the urolith core can differ in composition from that of the body.
Additional diagnostics based on urolith type.
Struvite
CaOx
Cystine
Urate
Struvite
- Urine culture at diagnosis
- Identify underlying causes of UTI
CaOx
- Serum total and ionized calcium
- Genetic testing
Cystine
- Urinary cystine quantification
- Genetic testing
Urate
- Bile acid test (PSS)
- Genetic testing
Treatment of urolithiasis.
All types: promote water intake (USG ≤1.020)
Dissolution with Diet, medication (works for Struvite, urate, cystine)
Removal:
Indications: clinical signs, urethral obstruction, recurrent infection.
Radiographs a week or less prior.
Minimally invasive procedures
include Voiding urohydropropulsion, basket removal, lithotripsy, percutaneous cystolithotomy.
Cystotomy (risk of Suture-induced urolith recurrence)
Voiding urohydropropulsion
is a minimally invasive procedure used to remove small bladder stones (uroliths) from animals, typically dogs and cats.
It involves filling the bladder with sterile fluid to distend it and then using controlled pressure to expel the stones through the urethra.
This technique is effective for small, smooth stones and is often chosen because it avoids surgery, minimizing recovery time and reducing risks for the patient.
basket removal
Basket removal for urolithiasis is a procedure used to extract stones (uroliths) from the urinary tract, typically using a cystoscope and a specialized wire basket device.
The basket is carefully inserted into the bladder or ureter, where it is maneuvered to capture the stones.
Once the stones are securely within the basket, they are gently removed through the urinary tract. This minimally invasive technique is commonly used for smaller stones and allows for a quicker recovery than open surgery.
lithotripsy
Lithotripsy for urolithiasis is a non-invasive procedure that breaks down urinary stones (uroliths) into smaller fragments, allowing them to be naturally expelled through the urinary tract.
It uses focused shock waves or laser energy to fragment the stones without the need for surgery.
Lithotripsy is commonly used for stones that are too large to pass on their own and offers a quicker recovery compared to more invasive techniques.
percutaneous cystolithotomy
Percutaneous cystolithotomy is a minimally invasive surgical procedure used to remove bladder stones (uroliths) in cases where non-surgical methods are ineffective.
It involves making a small incision through the skin and bladder wall to insert instruments that directly access and remove the stones. This technique provides an alternative to open surgery, offering a shorter recovery time and reduced discomfort for patients.
Basically the same as traditional surgery but uses smaller incision and an instruments to fish the stones out.
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
Contraindications for dissolution of struvite uroliths. (2)
Urethral obstruction
Comorbidities that prevent feeding of a therapeutic dissolution diet
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
What mechanism in portosystemic shunts predisposes animals to urate urolithiasis?
(PSS) divert blood away from the liver, impairing the liver’s ability to metabolize ammonia and uric acid.
This reduced hepatic processing leads to increased blood levels of uric acid, which is then excreted in the urine.
The elevated uric acid concentration, combined with altered urinary pH and reduced urine flow, creates a favorable environment for the formation of urate uroliths (stones).
Describe reasons for Dissolution failure
Wrong urolith type
Noncompliance with diet/medication
Premature discontinuation of therapy
Inappropriate antimicrobial selection in case of struvite
Describe monitoring after initiation of urolith dissolution.
UA at 1 month, then q3-6m Until target pH and USG.
Imaging at 1 and 3-6 months, then q6-12m To identify recurrence.
Struvite: urine culture at 1 month, if lower urinary tract signs return, q3m with history of recurrent UTIs.
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.
Typically, CaOx stones are found in what type of cats?
middle-aged to older, male neutered cats.
Burmese, Himalayan, and Persian breeds are predisposed to CaOx stone formation.
Feline struvite stones are typically sterile, in contrast to canine struvite stones,
and are more commonly found in
middle-aged female cats.
Struvite crystals are often found in the urine of cats with lower urinary tract disease; however, occasionally they can also be seen in cats without evidence of urolithiasis.
Domestic Medium hair (DMH) cats are at an
increased risk compared to other breeds.
the third most commonly reported cystoliths in cats.
Urate stones are the third most commonly reported cystoliths in cats.
Signalment of typical urate stone feline patient.
Males appear to be at an increased risk, but this could be because more stones are submitted from the male population due to lower urinary obstruction.
Most affected cats are 4-10 years of age, with the mean age of urate stone formers being younger than other types of stone formers.
Breed predisposition: ocicat, egyptian mau, siamese, burman
Pathogenesis of calcium oxalate stones.
Urinary calcium and oxalate concentrations depend on dietary intake, intestinal absorption, and renal tubular excretion.
Calcium: metabolic acidosis, hypercalcemia.
Urinary oxalate concentrations are 15× more potent than calcium concentrations in affecting CaOx saturation.
Oxalic acid absorption and excretion are affected by genetics, the amount of oxalate present in the diet, nutritional deficiencies (such as vitamin B6 in experimental settings), and intestinal flora.
Aciduria leads to increased risk of CaOx, urate, and cystine stone formation in cats.
Pathogenesis of struvite stones.
Sterile (11% bacterial)
Alkaline urine (Low animal protein diet, distal renal tubular acidosis, family history of struvite urolithiasis)
Pathogenesis of urate stones.
Any form of severe hepatic dysfunction can predispose cats to forming purine stones.
Clinical signs of urolithiasis in cats.
Ddx?
Asymptomatic or,
Lower urinary tract signs:
Hematuria, pollakiuria, periuria, stranguria
Differential diagnoses:
FIC
UTI
Neoplasia
Some conditions in cats that could predispose to urinary stone formation include: (4)
liver disease (such as portosystemic shunts),
chronic kidney disease,
hypercalcemia, or
diabetes mellitus.
Acidic urine in cats can lead to what types of stone formation? (3)
ammonium urate, silica, cystine
Alkaline urine in cats can lead to what types of stone formation? (3)
struvite,
calcium carbonate,
calcium phosphate (apatite)
Mineralized stones that are most commonly visualized with radiographs include (4)
CaOx, calcium apatite, struvite, and silica.
Most cystine and ammonium urate stones are nonmineralized and therefore not typically visible on radiographs (less visible, thus something may be seen).
The initial evaluation for CaOx stones should include a thorough assessment for underlying causes.
What should you check from biochemistry?
Serum ionized calcium concentration should be measured in any cat that is suspected of having CaOx stones.
If hypercalcemia is confirmed, measurement of parathyroid hormone, parathyroid hormone-related protein, and possibly serum vitamin D levels is recommended.
Treatment by dissolution in cats for what stone types? (3)
Struvite, cystine, urate
Contraindications to medical dissolution of suspected or confirmed struvite, cystine, or urate stones include the inability to medicate the cat, if the cat’s diet cannot be switched due to comorbidities, the cat has a history of urethral obstruction, or the stone is so large that it cannot be bathed in an appropriate amount of urine.
Indications for surgical removal of stones in cats.
have a high likelihood of causing urinary tract obstruction, have already caused urinary tract obstruction, or are causing clinical signs.
Treatment of CaOx in cats.
Cannot be medically dissolved.
Imaging 4 weeks, 3 and 6 months after removal.
Prevention:
Alkalinizing Diet
Increase water intake (USG <1.030)
Potassium citrate if diet is insufficient
(Alkalinizing (pH 7))
Hydrochlorothiazide
Thiazide diuretic
Enhances renal tubular reabsorption of filtered Ca
Manage the cause of hypercalcemia
Treatment of struvite in cats.
Dissolution diet (in 1-4 w (5 m)), Radiography after 2-4 w.
Uroliths should be 33-100% smaller.
Minimal change in size: not struvite, mixed composition, owner.
Continue diet for 2-4 w following radiographic dissolution.
Increase urine volume, reduce urine pH <7, adjust levels of Mg and P minerals in urine.
Treatment - urate in cats.
Surgical removal
Prevention with Protein-restricted alkalinizing diet. Wet food preferred.
Monitoring with Periodic U/S
Which common canine uroliths are smooth on xray and which ones are rough?
struvite are usually smooth
CaOx are usually a bit rough/rosette shaped
