Struvite- Why won’t the urolith dissolve?
BY DR ANNABEL ROBERTSON - APRIL 20, 2020 - URINARY & KIDNEY
A 2 year old female spayed Dachshund presents to your practice with a history of haematuria and pollakiuria. You take radiographs and see a 3cm round stone of moderate opacity in the bladder. You send the urine to the lab for culture and sensitivity, and it returns a positive culture for Klebsiella that is sensitive to most antibiotics. Given this combination of factors you have reached the conclusion the stone type this patient most likely has is a struvite. You decide to start the dog on Hill’s Prescription Diet c/d Multicare Canine and antibiotics. Two weeks later there has been no reduction in the size or change in density of the urolith on radiographs. What are the next steps?
Check owner compliance
Has the owner been feeding the c/d Multicare food exclusively? A common reason for failure of a struvite stone to dissolve is poor owner compliance. This is often due to a lack of understanding by the owner, and miscommunication by the vet. c/d Multicare works to dissolve struvite stones by producing urine with an under-saturated relative super saturation (RSS) for struvite. It is important to explain the reasons the pet needs to be on the diet exclusively at the first consult, so the client understands the implications of non-compliance.
Top Tip- Check the client understands at the end of the consult by asking them to repeat the plan back to you. This way you can clear up any misunderstanding before they leave the clinic.
Look for an infection
Struvite stones in dogs are commonly associated with an underlying urinary tract infection (UTI). Staphylococcus spp, Proteus spp and other urease producing bacteria are common causes of UTI’s in dogs, and result in alkalinisation of the urine. Struvite rapidly precipitates in alkaline pH and stones can thus form very quickly (days-weeks). Infections are more common in female dogs due to their anatomical differences.
It is imperative to always perform a culture and sensitivity of the urine as bacteria are not necessarily visible on urine sediment examination. Because viable bacteria may be released during dissolution appropriate antibiotics should be continued throughout the entire dissolution period.
Unless the underlying cause of the UTI has been addressed, the infection is likely to recur and struvite can reappear despite feeding a urinary friendly diet. Ensure you address underlying factors for infection such as excessive vulval folds, polyps, strictures, peri-vulvar dermatitis and hyperadrenocorticism.
Evaluate stone size
A struvite stone must be bathed in under-saturated urine for dissolution to be effective. This is why dissolution for urethroliths and nephroliths or large uroliths is often ineffective. It is preferable to remove large bladder stones via cystotomy and submit them for urolith analysis.
Top Tip- Hill’s offers a free urolith analysis service via the Minnesota Urolith Center. Simply contact your Hill’s rep to find out more.
Consider you may be managing a different stone type
Sometimes, despite our best assessment, we have not correctly identified the stone. Instead we could be treating a different or compound urolith such as struvite-calcium phosphate carbonate (CPC). Therefore, if you are certain all the reasons for lack of dissolution listed here have been accounted for, it is very probable you could be faced with a different urolith. Dissolution is therefore not going to be possible in this case. Check out the blog on guesstimating urolith composition for tips on how you can predict stone type.
A note on struvite
Did you know? The American College of Veterinary Internal Medicine (ACVIM) has released guidelines on the management of different uroliths in cats and dogs? It states that ‘Struvite uroliths should be medically dissolved unless… medications or dissolution foods cannot be administered or are contraindicated, the uroliths cannot be adequately bathed in modified urine (eg, urinary obstruction, large solitary urocystoliths occupying almost all of the urinary bladder), or uncontrollable infection despite appropriate medical management and owner compliance.1
Do you have a tricky case and need our help? Or have you received urolith results but are unsure on the long term dietary recommendation? Contact us at the Hill’s Helpline 1800 800 733.
Dr Annabel Robertson BVSc (Hons) MANZCVSc MBA, Hills Technical Services Veterinarian
Annabel graduated from the University of Melbourne with honours in 2008. Since then she has worked as a small animal veterinarian in private practice in Australia and the UK. She also completed an internship in small animal medicine during this time and sat her membership in small animal internal medicine in 2012, and finished her MBA in 2015. Annabel joined the Hill’s team in 2015 as a technical services vet in Melbourne.