Urolithiasis Flashcards
What can contribute to the formation of uroliths?
pH Retention of urine Increased concentration of salt Infection Decreased concentration of crystalisation inhibitors (GAGs, citrates etc) Normally a nidus
What are the types of urolith that are common
Struvite Ca Oxalate Cystine Purine Silica Ca Phosphate Mixed
What can predispose to Ca Oxalate crystals
High calcium
High oxaluria
Ca in the water source
Concurrent disease
What can cause calciuria?
Different types.
- Absorptive - excess absorption in the intestines, leads to renal leak, therefore decreased renal reabsoprtion there fore increased PTH which leads to increased Ca absorption and release in bone
- Resoptive - excess skeletal mobilisation of Ca - primary hyperparathyroidism
What can cause oxaluria?
Produced by metabolism of glyoxalate, glycine, ascorbic acid in the liver and excreted in the urine
AAs from meat protein metabolised to oxalate
Not reported in dogs
/How can water source predispose to Ca Ox crystals
Increased Na or Ca in the water
Abscence of Zn which chelates Zn
No studies in dogs
Not a thing in cats
What are some inhibitors of Ca Ox?
most important are citrate and Mg as they form a v insoluble complex
Also:
Pyrophosphate - related to Phos, decrease phos, increased risk
GAGs
Nephrocalcin
Tamm Horsfall mucoprotein
What concurrent diseases pre-dispose to calcium oxalate?
Cushings hyper PTH vitaminosis D Paraneoplastic hypercalcaemia Meds - frusemide or steroids
How can you dx Ca Ox stones?
UA -ph <6.5
Crystals only may be present
Can be seen on rads
May see high Ca on bloods
How do you treat Ca Ox stones?
Not ammenable to dissolution
For obstruction - retrograde hydropulsion then cystotomy or perineal urethrostomy if needed
If stones small enough to pass then increase u+ then repeat rads
When should you use surgery to remove uroliths?
Recurrent infections Blockage Painful Severe h+ u+ Increasing in size/ damaging renal tissue Monitor with rads every 3-6m
How should a diet be made for Ca Ox stones?
Increase water intake Wet diet or add water Diet non rich or restricted Ca Decent phos leves Moderate Na levels to increase diuresis, but too much predisposes
What should you do if the pH is not high enough even with a Ca Ox diet (s/o LUT support or Hills u/d)
Or what if there is still crystaluria?
Add K citrate
Feed moderate to high fibre and low fat
Thiazide diuretics - they decrease urinary Ca excretion, and concentraton, cause subclinical volume depletion which increases proximal tubular reabsorpion of Ca and Na
What does K citrate do?
increases urinary pH by decreasing tubular reabsoprtion of citrate and increasing urinary citrate excretion
What supplements should be avoided with Ca Ox?
Vits C or D
What is the recurrence rate of Ca Ox?
up to 50% in 3 years
When is the presence of crystals important?
Previous stones
Crystal that is not struvite or Ca Ox
Predisposed breed
Under treatment
Which breeds have a higher occurance of struvites?
Lhasa Apso, Cockers, mini poodle
What are Ix findings specific for struvites
Culture more commonly +ve
If negative, ensure an anaerobic culture is performed on the centre of the stone
May see inflammation on bloods
How do you monitor dissolution of struvites?
Can take approx 3 months Imaging and UA every m Tx 4 weeks beyond radiographic cure Do Sx if C/S are severe, obstruction, pyelonephritis, immature dog. UTI control more important than diet
Outline the use of Hills S/d for struvite dissolution
not long term
Low protein, Mg, phos
Acidifies for diuresis
Avoid if pregnant, high BP, renal issue, need for low fat
May cause low BUN and high ALP - if bloods show no changes then O is likely also feeding pet something else
What should you do if the diet is not modifying the pH enough?
Consider UTI not being under control
Can give AHA, an inhibitor of urease, however not to patients with renal issues as there are many side effects.
What should you consider if the uroliths increase in size despite treatment?
Mixed uroltih Wrong Dx Further release of bacteria non compliant O Consider sx
How do you monitor struvites post dissolution?
Culture approx every 2-4m
Diet alone cannot control struvite stones if present
Consider cystoscopy or bladder biopsy if recurring
How do you prevent sterile struvites?
Keep pH 7
Increase water and u+
diet as for UTI struvites
What specific Ix are needed for purine stones
Biochem may show underlying disease
do BA stim in any breed not a dalmation
Rads - are radiolucent so double contrast cystogram for nephroliths
US - stones and shunts
How do you treat purine stones
Sx if obstruction or PSS
Low purine diet - high water
Allopurinol (xanthine oxidase inhibitor)
Increase pH - aim for 7, can give Na Bicarb or K citrate
Tx UTI
takes 8-12 weeks
hills u/d - no Na, non acidifying, low purine, K citrate in and Ca Carbonate
if dog has DCM, can get CHF with low protein diet, so give renal diet and allopurinol
What is a caveat to allopurinol treatment?
Must be low protein diet or can get a xanthine shell
What pH do you need to prevent cysteine?
> 7.2
Cysteine is freely filtered and actively reabsorbed. If there are stones, there is ddefective absorption
What specific ix findings are there with cysteine?
Cyanide nitroprusside test +ve
increase AA in urine AA profile
Contrast studies needed for rads
How can you do medical dissolution of cysteine stones?
2MPG -combines with cysteine to make more soluble, can get s/e Hills u/d diet urine alkalinisers - K+ citrate At least 10 weeks, often a long time Monitor every 4-6 weeks
How do you prevent cysteine stones
2MPG or u+ alkalinisers
Low protein unless has DCM
Decreased risk with age
Outline silica stones
not pH dependent more males, any age GSD/ old english shepherds Jackstone appearance Poss d/t increased excretion of silica Increased plant diet thought to be a risk factor, also talc and kaolin Radiodense
How do you treat silica stones
Can’t disolve
Low veg diet
Sx if obstructing
What can cause Ca Phophate stones/ crystals
UTI from urease
high urine pH
high ca/ high PTH
Can irritate epithelium and be a nidus for struvite
How do you treat Ca Phosphate stones?
Often small so high risk of obstruction, so often recommend Sx
May need to remove parathyroid if high PTH
Who gets dried blood clot stones
Cats
outline ureteral stones
Often start in renal pelvis and move causing a partial or complete obstruction
can get rupture
In dog normall struvite or Ca ox
Don’t always get signs, may be incidental
may not see on rads as so small so U/S easier
Most sensitive test for changes in the ureter is excretory urography
if no movement in 3-5 days consider intervention
Tx - lithotripsy, sx or medical. Can do unilateral nephrectomy if v bad one side and all fine on other
Outline excretory urography
Most sensitive test for changes in the ureter
May see increased size if obsruction
In chronic disease the ureters are dilated and tortuous
Avoid in patients with renal issues
What are the easiest stones to dissolve with lithotripsy?
Struvite easiest, then Ca Ox, then urate, then cysteine
