scott@vtx-cpd.com

Replying to Talia C. 02/12/2024 - 08:55

Dear Talia,

Thank you for sharing this case. Pyelonephritis can be such a diagnostic puzzle? The combination of fever, weight loss, and reduced appetite alongside the initial ultrasound findings and positive E. coli culture certainly pointed toward pyelonephritis as the likely culprit. Starting enrofloxacin was a solid choice, and her clinical response after the two-week course was really encouraging. That said, I agree with your instincts—it might’ve been better to extend the course to 4–6 weeks, given the nature of renal infections and their tendency to hang around if not completely eradicated. These infections like to play the long game!

At the three-month follow-up, I think you did the right thing by repeating the ultrasound and urine culture. Even though she’s clinically well now, the residual urine culture positivity raises the question of whether we’re dealing with asymptomatic bacteriuria (ASB) or some lingering infection. The ultrasound findings of mild pelvic dilation and increased cortical echogenicity could well be residual scarring from the earlier infection. It’s always a bit tricky to interpret those changes—renal pelvic dilation can be non-specific, and chronic changes don’t necessarily mean ongoing infection. But I would agree it’s worth keeping an eye on.

Now, about the current culture result showing E. coli in her urine. In a cat who’s bright, eating, and symptom-free, I’d lean toward considering this as ASB rather than an active infection. Studies suggest treating ASB isn’t always beneficial and can even encourage resistance. That said, if she starts showing any clinical signs—lethargy, dysuria, or even subtle changes like hiding more—I’d definitely revisit the idea of treating her with a longer antibiotic course, ideally guided by sensitivity testing.

When it comes to further management, here’s what I’d suggest: No immediate antibiotics. Since she’s well in herself and there are no systemic signs, we can probably leave the E. coli alone for now. Just keep monitoring her closely. Recheck urine culture in 2–3 months. If it’s still positive but she remains symptom-free, I’d still hold off on antibiotics unless her bloodwork (e.g., creatinine, SAA) or clinical signs change. Routine follow-ups. Periodic ultrasounds and blood checks will help keep tabs on her kidney function and detect any recurrence early. It’s also a good opportunity to discuss any subtle behaviour changes with her owner.

I’d be slightly cautious about relying on enrofloxacin for future treatment in this girl if she does need antibiotics again. There have been occasional reports of retinal toxicity in cats on enrofloxacin, especially at higher doses, so it might be worth considering alternatives like marbofloxacin or cefpodoxime instead. It’s a small risk, but I’d rather play it safe when we have options.

Let me know how she gets on or if you’d like to chat through anything further!

Warm regards,

Scott 🙂

Replying to Rachel C. 12/12/2024 - 14:33

Hi Rachel,

I completely understand your concerns—this is such a common scenario in general practice, and it can be challenging to strike the right balance between monitoring and action while managing owner expectations.

For geriatric patients on long-term NSAIDs, mild increases in ALT and ALP are not uncommon. As long as the dog is clinically well and these changes are mild (e.g., less than 2-3 times the upper reference interval), monitoring is often a reasonable first step. I typically recommend rechecking bloodwork in 2-4 weeks to observe trends. If values remain stable or improve, continued monitoring every 3-6 months, aligned with routine NSAID check-ins, may suffice.

However, I would investigate further if:

Enzyme elevations become significant (e.g., >4-5 times the upper reference interval).
Other abnormalities appear, such as hypoalbuminemia or elevated bile acids.
Clinical signs like anorexia, vomiting, or lethargy develop.
In such cases, additional diagnostics like an abdominal ultrasound can help assess for underlying liver dysfunction.

When owners ask about “something to give,” I often suggest liver-supportive supplements such as SAM-e, milk thistle (silymarin), or combination products like Denamarin. While evidence varies, these are generally safe and may offer hepatoprotective benefits.

Carprofen-Induced Liver Injury
It’s important to consider potential carprofen-induced hepatotoxicity, an idiosyncratic reaction seen in some dogs, typically within the first month of treatment. Clinical signs include anorexia, vomiting, and icterus, often accompanied by elevated ALT, ALP, and bilirubin levels. The condition can improve with prompt discontinuation of carprofen and supportive care. Interestingly, Labradors appear over-represented, although this might reflect breed popularity. Histopathological findings often reveal bridging hepatic necrosis, and chronic liver disease as a sequel has not been clearly established.

Additionally, a study published in the J Am Vet Med Assoc (“Hepatocellular toxicosis associated with administration of carprofen in 21 dogs”) highlighted variable clinical courses among affected dogs. While most recovered after discontinuation of the drug, some cases showed associated renal abnormalities, likely secondary to tubular disease.

Let me know your thoughts or if you’d like to discuss this further!

Best,

Scott 🩺🐾

Replying to Jenny G. 29/11/2024 - 12:25

Thank you again Jenny.

Scott 🙂

Replying to Talia C. 24/11/2024 - 20:40

Dear Talia,

Thank you for your reply! It sounds like you have a very systematic and thorough plan in place, which is great for these tricky cases. You’re absolutely correct in your understanding of the response to desmopressin (synthetic ADH). The diagnostic utility of a DDAVP trial lies in its ability to differentiate between central diabetes insipidus (CDI), nephrogenic diabetes insipidus (NDI), and psychogenic polydipsia (PD), as you outlined. A marked increase in urine concentration, with a urine specific gravity (USG) above 1.025 or a rise of over 50% from baseline, strongly supports CDI. In contrast, only minimal improvement in USG is expected with NDI because the kidneys are unresponsive to ADH. Dogs with psychogenic polydipsia may show a mild reduction in urine output and water intake as plasma osmolality normalizes, but this response is often subtle.

The morning USG of 1.028 does introduce some complexity. While it suggests some ability to concentrate urine, it doesn’t entirely rule out CDI, as partial CDI cases may show intermittent concentrating ability. Similarly, primary polydipsia can also present with variable USG patterns, making it challenging to differentiate between the two based on USG alone.

If there is still concern about being “stuck” between NDI and primary PD, adding SDMA testing and advanced imaging are excellent next steps to rule out subtle renal disease or structural abnormalities. Iohexol clearance testing could also be considered, as it provides a precise measure of glomerular filtration rate (GFR) and might uncover early renal dysfunction not evident on routine tests. Monitoring USG at different intervals, particularly during periods of water restriction if feasible, may also help establish a clearer pattern of water handling and concentration ability.

The planned full abdominal ultrasound is an important step and will help exclude other systemic causes, particularly structural or functional abnormalities that could impact water balance. Chronic conditions, such as low-grade inflammation or mild endocrine issues, could also contribute to her clinical signs and would benefit from this thorough evaluation.

If you proceed with a DDAVP trial, I recommend carefully monitoring water intake and USG over several days before and after administration. While this won’t definitively distinguish between all potential causes, it often provides enough diagnostic clarity to inform further management or investigations. Please let me know how she progresses following the ultrasound and any additional testing.

Best regards,

Scott

Replying to Lesley M. 22/11/2024 - 22:36

Thank you so much and thank you again for sharing via email.

I will make sure to post here!

Scott 🙂