Calculi in Dogs (and Other Pets)

Question 1

Do you always see crystaluria when uroliths are present?

Answer 1

If crystals retain – they may grow and aggregate to form stones. Crystals make up stones – need lots of them to group to make a stone

No, they are separate, may have different stone to crystals seen in urine?

Crystaluria is not synonomous with formation of uroliths – nor is crystalluria evidence of stone forming tendency (even if animal has loads of crystals à doesn’t mean its going to get a stone)

Get stones – if don’t urinate often, certain diets, temperature, bad luck

Question 2

What percentage of uroliths in the dog are located in the kidneys or ureters? Note surgical removal of uroliths from the kidney and ureter carries considerable risks. This is not a procedure routinely performed in general practice.

Answer 2

Lower chance of getting stone in kidney or ureter to elsewhere

Most common place: urethra/bladder, then ureter then kidney?

Horse: bladder, urethra, renal pelvis, ureter

Question 3

Why is it common to get secondary urinary tract infections with uroliths?

Answer 3

Cause obstructions?

UTI is both a cause and consequence of uroliths because infection with bacteria that is urase producing – then will get struvite uroliths. Presence of uroliths can precipitate UTI by obstruction of mucosal lining of bladder and incomplete urine voiding and sequestration of microorganisms

Question 4

Which crystals may occasionally be found in the urine of normal dogs?

Answer 4

Normal dogs – struvite can be normal, calcium oxalate (high Ca diet)

Struvite, Ca oxalate and urate more commonly found in dogs

Ca dihydrate and struvite à storage more than 1 hour without refridgeration

Question 5

What clinical signs may you see with urolithiasis?

Answer 5

Dysuria, haematuria, stranguria (straining), lethargy

Question 6

If you suspect that an animal may have urolithiasis (based on its clinical signs) what would a sensible diagnostic plan include?

Answer 6

Urine analysis – sediment, radiographs, US, contrast studies?

· Palpation of distended bladder, potential palpation of uroliths.

· Urinalysis – pH, sediment exam.

· US of bladder – look for shadows caused by uroliths (useful for radiolucent uroliths). Radiography – struvite/oxalate calcium phosphate and silca radiopaque (cystine and urate less radiopaque – may need double contrast cystography). Culture – urease producing bacteria eg staphylococci associated with struvite urolithiasis. Biochem – hypercalcaemia associated with calcium oxalate urolithiasis

Question 7

In which cases would you NOT attempt medical dissolution of uroliths?

Answer 7

If obstruction present

Question 8

Animals that have an acute complete obstruction of the urethra with a urolith are a genuine emergency and will require a number of immediate treatments – please list these in order of priority

Answer 8

· Bloods – hyperK+? (may need to reduce, protection of heart)

· Stabilise patient : Fluids? Only if no obstruction. Maybe just do it anyway and repeat Cystocentesis to remove – animals needs fluids – will die from hypovolemic shock not from rupture bladder

· Cystocentesis to remove some of the pressure?

· Try to catherterise/retropulsion

Question 9

For each of the following methods of Urolith removal briefly list the pluses and minuses. All of these methods require a general anaesthetic

Answer 9

· Cystotomy : surgical incision, good as can remove stones, bad as poorer prognosis – traumatic, bladder leak after poor sealing, GA risks. U

· Laparoscopic assisted cystotomy: less traumatic – make cauterise the hole, grab and pinch together? Use stone baskets passed through cystoscope and pull stones up.

· Voiding Urohydropulsion: fill bladder with saline under GA and squeeze out

· Cystoscopy assisted techniques :

· Lithotripsy: laser, cystoscopy to place a laser in direct contact withuroliths with fragmentation, blast the stone. YAG (laser energy) – Holmium lag laser, absorbed – limited risk. After this, then squeeze bladder or voiding urohydropulsion to remove the fragments. Good: safer than open surgical removal, less damage to bladder wall. Complications – partial to complete obstruction of ureter (kidney) by fragments. Use a scope

Question 10

What is retro-urohydropropulsion and how is it performed?

Answer 10

For urethroliths

· Retrograde urohydropulsion – push back into bladder with catheter, then release pressure, then there is less panic.

· GA and lubrication, use end hole catheter. 2 person procedure, one person ready to flush stones, rectal exam other person to squash urethra against pelvis, then fill up, then when feel pressure, person in rectum removes finger and then more force of stone back into bladder. Care not to rupture urethra

Question 11

Which stones may be dissolved via medical therapy (diet manipulation to adjust the composition of urine)

Answer 11

Struvite (short term low protein acidifying diet) , maybe urate (can try, low protein diet, lots of water to flush through, if it doesn’t work then may need to remove), Cysteine

Cant dissolve Calcium oxalate (formed by acidic urine)

Question 12

Why is it always important to determine the composition of any uroliths you remove?

Answer 12

Depends on treatment offered! Medical vs Surgical

If you acidify diet to try to treat struvite then exacerbate then Ca oxalate growth. And vice versa.

Help you find a cause? Note that urate ones can be caused by shunts – may show underlying issue, or severe hepatic disease

Cysteine – caused by defect in renal tubular transport – may be other renal issues going on

Struvite may show UTI – so tx this

Ca monohydrate crustals – ethylene glycol or chocolate toxicity

Question 13

Make a plan for the medical dissolution and prevention of recurrence of struvite uroliths located in the bladder of a female dog.

Answer 13

Need to give low protein, acidifying diet

Dissolution via dietary modification – acidifying diet, reduced high quality protein, reduced phosphorous and magnesium (decrease intake of struvite precursors) Treat UTI – struvite calculi usually follow infection with urease-producing organims (Staphylococcus, Proteusor ureaplasma) Increase fluid intake – to decrease concentration of urine which decreases saturation with minerals that make up the stones. Urinary acidifier – to decrease risk of future struvite stone formation (but doesn’t have many additional benefits if acidifying diet is already producing acidic urine)

Question 14

Given the length of therapy is medical or surgical therapy for struvite uroliths more expensive?

Answer 14

Even if you do surgical removal – still need preventative diet – so ££

So maybe just do diet in long term

Question 15

What percentage of uroliths will recur without preventive therapy?

Answer 15

Ca stones 60% recurrence over 3 years

Lecture notes: Struvite in dogs = Usually with UTI - urease producing Staph, NH4 precipitates with Mg & PO4. HCO3 = ­pH, Treat UTI, Short term low protein acidifying diet, Prevention - not required unless sterile struvite

Will recur more with UTIs.

Question 16

What are the major differences in the medical treatment (or prevention of recurrence post surgical removal) of the following uroliths

Answer 16

· Oxalate - cant medically (diet) calcium oxalate, conflicting advice about prevention with diet – maybe more common in acidifying diet, maybe alkalinise. Avoid Ca supplements and high oxalate food – chocolate, nuts, spinach. Use high moisture food – due to desired increased water consumption (to flush out).

· Urates/Purines - low purine diet, low prtein diet, make urine more alkaline. Xanthine oxidase inhibition and elimtae UTIs. Hill’s prescription diet with reduced protein and purine content to produce alkaline urine!

· Cystine - prevent with diet, Hills prescription diet , K+ citrate can be added

· Calcium Phosphate – can get as a result of UTI – in which case penecillins work against urease producing bacteria – stop UTIs

Question 17

Complete this table

Answer 17

Question 18

Complete this table

Answer 18