Wednesday, April 7, 2010

16. urinary stones in dogs

The Death Sentence for Producing Urinary Stones - How to prevent recurrences in struvite and other urinary stone formation
Dr Sing Kong Yuen, BVMS (Glasgow), MRCVS
Updated: 08 April, 2010

Many times, it is a death sentence when the pet dog produces urinary stones again as the average Singaporean dog owner feels that the diagnosis by clinical signs and diagnostic imaging, the surgical treatment, hospitalisation, nursing care and medication from around S$800 to over $2,500 are "expensive". Unfortunately, urinary stones do recur in some dogs such as the Miniature Schnauzer.

Stones are usually found in the bladder and urethra. Less than 4% of urolithiasis cases are found in the kidneys or ureter (hydronephrosis, acute renal failure).
1. Accurate analysis. Stone analysis by Hills Pet Nutrition using optical crystallography or infra-red spectrometry or a laboratory able to analyse stones. Crystalluria or urine analysis may not be accurate. Characteristic shapes on radiographs and by visual examination is not a reliable guide to their composition. Oxalates are said to be highly radiodense and silica are radiodense with jackstone shape. Struvites are moderately to highly radiodense but is associated with urinary tract infection (urease production) and alkaline pH. Calcium oxalates are associated with hypercalcaemia.

2. Treat UTI e.g. struvite stones.
3. Surgical removal by cystotomy (calcium uroliths) or medical dissolution by dietary manipulation of the urine pH (applies only to struvites, urate and cystine). Ureteroliths and urethroliths cannot be dissolved and should be surgically or manually removed. All uroliths dissolve at the same rate, so it is not the number. But largest stones dissolve slower than smaller ones. The owner may not want to pay for the regular X-rays to monitor dissolution of the stones in real life. The owner must be warned that it is possible that bladder stones may obstruct the urethra when they get dissolved to smaller size. In practice, I have a case where a vet suggested feeding home cooked food but the female Miniature Schnauzer had a stone as large as a quail's egg. The stone did not dissolve. I suspected that the vet just advised home-cooked food and gave antibiotics. I don't think the owner gave the acidification tablets after some days or were not given any. In any case, the dog kept peeing blood. I had it surgically removed and the dog was OK for the past years. It is said that it takes as long as 7 months to get the large struvite stones dissolved. When you see the large quail egg stone (in one of my case studies), you will wonder whether it can be dissolved medically at that size.

4. Lithotripsy or sonic dissolution. Not available in Singapore.

5. Prevent or reduce recurrence by getting the dog to pee less concentrated urine (target at USG <1.020).
How to do it? No dry food. Add water into food. Pet fountain, multiple water bowls around the house, ice cubes in water, add something inside water to encourage drinking. I would advise milk if the dog is lactose tolerant.

6. Monitor by regular imaging. Few Singapore owners spare the time or money to get this done. They just seem to have no time.
Some of my tips to prevent recurrences of struvite stones are:

1. BREED. Breeds like the Miniature Schnauzer are prone to producing urinary stones. Urinary examination at least 3-monthly will be ideal. If not, during the half yearly wellness examination or yearly vaccination, ask your vet to do a urinary analysis.

2. DIET. No dry dog food definitely. No canned foods or treats. Special low stone prescription diet or home-cooked food.

3. URINE pH to be acidic if struvite stones have formed. USG to be less than 1.020. Red and White Blood Cells measured weekly using dipsticks in collaboration with your vet.

4. WATER INTAKE. Measure diligently and scientifically 24-hourly water drunk in collaboration with your vet. Some sedentary dogs need to be encouraged to drink by more exercise or supervision.

5. ACIDIFICATION OF THE URINE if the urine pH is 7.0 and higher in collaboration with your vet.

6. BLADDER PALPATION. If stones or a crackling gassy sound are felt, it is bad news. Consult your vet promptly.

2 female dogs with blood in the urine. Both had dry dog food. The Schnauzer, peeing out stones, was fed home-cooked food at the same time as another dog (Golden Retriever) was fed dry food by the maid 8 months ago after consulting me about "no surgery". She was given acidification tablets and C/D diet for 1 month and had no longer produced stones. She might have eaten some dry food and produced stones 8 months after my consultation.

The Cocker Spaniel had fish-based dry dog food for 8 years and was observed to have haematuria 2 months ago. A vet advised medication to dissolve the stones in view of the high anaesthetic risk of operating on a senior dog.
The objective is to prevent struvite crystal formation by ensuring that the bladder is free from bacterial infections and that the urine pH is alkaline. The dog owner has to be educated in prevention and to take good care post-surgery in collaboration with their vet keeping proper records. Unfortunately, few owners bother. A recurrence means a death sentence usually during times of recession. The guidelines apply to the prevention of struvite (triple phosphate) urinary stones only.

INCIDENTAL FINDINGS OF A CALCULUS. Many Singapore owners are not interested in medical management by regular abdominal radiographs or surgical removal as the dog seems not to have any urinary problems after antibiotic treatment.

URINE pH required to form struvite stones is alkaline. Calcium oxalate and ammonium urate or urates (Acid to Normal). Cystine, silica and xanthine (acidic).

Struvite (magnesium ammonium phosphate) are most amenable to medical dissolution. Calculolytic diets have low protein, phosphorus and magnesium but high sodium content to produce diuresis and they acidify urine. Antibiotics based on bacterial culture. Dissolution may take 4 months or as long as 7 months. Surgical removal if urethral obstruction not relieved by retropulsion.

Calcium oxalate. Increased urinary calcium excretion may be due to increased GI calcium absorption, renal-leak hypercalciuria (tubular defect), hypercalcaemia or hyperadrenocortiicism. Surgical removal only. Correct hypercalcaemia, reduced protein, calcium and oxalae diet for absorptive hypercalciuria. urinary alklisation with potassium citrate. thiazide diuretics in dogs with recurrent cases eg. hydrochlorothiazide 2mg/k q 12 hr PO). No treatment for renal-leak hypercalciuria.

Ammonium urate. 96% Dalmatians. Dogs with liver disease of portosystemic shunts 4%. Calculoytic diets by urinary alkalisation e.g. Hills u/d but this takes many months. Allopurinol 30 mg/kg q 24 hr PO to reduce urate production by inhibiting enzyme xanthine oxidase WITH protein restricted food. Prolonged allopurinol treatment may result in xanthine crystalluria and urolithiasis.

acid urine. renal tubular disorder. surgical removal. medical management said to work. Alkalisation and protein restriction diet e.g. u/d. PLUS N-(2-mercaptopropionyl)-glycine (2-MPG) at 15-20mg/kg, 12 hr with diet for dissolution, then 15 mg/kg q 12 hr for prevention.

Bladder Stone case studies
The Vet's Best Is Not Good Enough


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