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Date:   09 February, 2012  

 Small animals - dogs, cats, hamsters, guinea pigs, turtles & rabbits
Recurrent urolithiasis in a Miniature Schnauzer
from calcium oxalate to struvite stones

Dr Sing Kong Yuen, BVMS (Glasgow), MRCVS

09 February, 2012 
Be Kind To Pets
Veterinary Education
Project 2010-0129
I hope this will be an interesting case for vet students trying to memorise their facts and figures on urolithiasis in the dog.

I review the following case as a vet said that that the recurrent urinary stone situation was due to the same calcium oxalate stones as in the first surgery of cystotomy. It was only 4 months ago that this dog had an operation and stones were taken out and analysed as calcium oxalate stones.

Veterinary medicine is full of surprises and challenges and that is why the vet must always be alert. The recurring stone problem was due to Struvite stones! This case illustrates the importance of the owner doing urine tests every month after the surgery and X-ray every 3 months.

But no owner in Singapore, in my experience, will bother to adopt this preventive advices. If stones are seen early on X-rays, they can be dissolved by dietary management (for Struvites) or flushed into the bladder and sucked out (urohydropropulsion). Therefore, there is no need for another surgery. The case review is as follows:
urinary stones again despite home-cooked food diet. why? toapayohvets miniature schnauzerPatient; Miniature Schnauzer, Male,
8 years, Salt & Pepper 48 hours after the 2nd cystotomy. He bit the vet nurse post-op and was best nursed at home as he does not bite family members. 
9.3 kg, 39.3C
Dysuria >7 days. Haematuria. Eats dry food. Now, anorexic.
Urethral obstruction. Catheter relieved obstruction. Cystotomy the next day. Owner advised prescription diet but was not interested. Would feed home-cooked food.
8.2 kg,  38.4C
Dysuria. Haematuria. Fed home-cooked food. Dr Vanessa said that the catheter could not pass through and the dog was biting. A prompt X-ray on a Friday evening and immediate surgery. Dog went home on Day 3. Dog not so aggressive now. Family is happy with good surgical outcome.  
pH=7 (5-8), SG 1.030 (1.005 - 1.030).
Protein +, Blood 4+, WBC 504, RBC 1440, Bacteria +, Crystals Nil

X-RAY. Small stones seen.

Urea = 7 (4.2 - 6.3)
Creatinine = 61 (89-177)
WBC = 13.6 (6-17) with neutrophils 93%. Absolute 12.6, lymphocytes 6.5%. Absolute 0.88
No hypercalcaemia

16.9.11 Cystotomy. Urinary stones removed by Vet 1

STONE ANALYSIS - multiple fragmented uroliths. CANINE CALCIUM OXALATE
Calcium oxalate monohydrate 100% stone, 5% shell
Calcium oxalate dihydrate 95% shell


MANAGING Calcium Oxalate Urolith prevention - do urinalysis and X-rays.
If urine SG >1.020 give canned food or add water to food
If urine pH <6.5, consider diets that produce less acidic urine eg. u/d or use urinary alkalinizers eg. K citrate If urine pH>6.5, USG <1.020, no crystals, repeat urinalysis monthly, then every 3-6 months.
Repeat X-ray every 6-12 months to detect Urolith recurrence early.
Repeat urine test and X-rays if signs - haematuria, pollakiuria, dysuria recur.

For calcium oxalate prevention,
1. Diets promoting urine pH <6.59 were at highest risk.

2. Avoid risk factors like hypercalciuria due to hypercalcaemia, metabolic acidosis, high sodium consumption and Vit D excess.

3. Feed canned foods and/or add more water to food so that urine pH is consistently <6.5.

4. Consider hydrochlorothiazide (2mg/kg q 12 hr) with highly recurrent urolithiasis in dogs without hypercalcaemia.

5. Consider potassium citrate (75mg/kg q 12-24 hr) if urine pH is consistently <6.5.

pH=9 (5-8), SG 1.025 (1.005 - 1.030)

Protein 2+, Blood 4+, WBC 0, RBC >2250, Bacteria +, Crystals Triple phosphate +, Amorphous phosphate 3+

Struvites stones can be dissolved by diet if they are small in size or removed by urohydropropulsion. Toa Payoh Vets, Singapore

X-RAY. 15 stones seen. bladder and behind os penis.
urinary stones again despite home-cooked food diet. why? toapayohvets miniature schnauzer

BLOOD TEST. Owner declined test.

3.2.12 Cystotomy. Urinary stones removed by Vet 1

STONE ANALYSIS - Sent stones to the lab

This is not a recurrent case of calcium oxalate urinary stones as the 2nd episode showed struvite stone formation.

If the owner had done urine tests monthly and X-ray 3-monthly, the struvite stones will be detected early and as small stones.

It is easier to remove without the need for surgery. Either using urohydropropulsion and sucking out the small stones or S/D diet to dissolve them.

STRUVITE stones are clinically insignificant if there is no urinary tract infection as bacteria-forming urease are required for struvite Urolith formation in dogs.

In this case, the urine had bacteria and had high alkaline pH  (pH= 9.0) favouring the urease-producing bacterial growth and subsequently the production of struvites (known as triple phosphates).

1. Voiding urohydropropulsion if small uroliths are present as seen in the X-ray. 
2. Medical dissolution with prescription dies in cases like struvites.
3. No clinical signs (dysuria, haematuria), leave stones alone inside the bladder.
4. With persistent clinical signs, remove uroliths
5. Send for stone analysis. See the case of:
Recurrent urolithiasis in a Shih Tzu
6. Vet to record advice to owner to do urinalysis every month and X-rays every 3 monthly to prevent recurrence or to treat early without surgery.

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