Replying to Talia C. 18/11/2024 - 17:06
Dear Talia,
I hope you are well!
Thank you for your detailed case description—this is indeed a challenging situation, and it’s great that you’ve already ruled out hyperadrenocorticism.
Primary Polydipsia vs. Other Causes:
Primary polydipsia (PD) can be difficult to confirm, especially in a multi-dog household where water intake cannot be accurately monitored. The USG variation in this case is interesting—morning concentration suggests some renal concentrating ability, but the subsequent low values during the day raise concerns about inappropriate diuresis.
While the morning USG of 1.028 shows some concentrating ability, it is still not maximally concentrated (e.g., >1.040).
The marked decrease in USG during the day suggests either significant water consumption or a potential inability to concentrate due to an underlying cause.
Given she is intact, consider whether hormonal factors related to her recent heat in May 2024 could play a role. While pyometra seems unlikely based on your ultrasound findings, conditions like oestrogen influence on the kidneys may contribute to altered water balance? It might be worth repeating the ultrasound. Could there be something more subtle happening in the uterus.
To further investigate the cause of her PU/PD, advanced imaging such as an abdominal ultrasound and thoracic radiographs would be logical next steps. These could help identify any occult disease or structural abnormalities contributing to her clinical signs, particularly given her history of recurrent UTIs. Alongside imaging, a desmopressin (DDAVP) trial would be a non-invasive way to explore the possibility of central diabetes insipidus (CDI). If her urine becomes concentrated after desmopressin administration, this would support a diagnosis of CDI.
Additional diagnostic options include measuring SDMA (symmetric dimethylarginine) to detect early renal dysfunction, which may not be apparent on routine biochemistry. Iohexol clearance testing could also be considered as a precise method for assessing glomerular filtration rate (GFR) if renal insufficiency remains a concern. Evaluating her renal function through a urine protein-to-creatinine ratio (UPC) would provide further insight into any subtle renal disease not evident on bloodwork or routine urinalysis.
Even though a water deprivation test is often used to differentiate between primary polydipsia, CDI, and nephrogenic diabetes insipidus (NDI), I would avoid this in her case due to the risk of dehydration and the availability of safer diagnostic approaches. This combination of imaging, targeted renal assessments, and a DDAVP trial offers a systematic and minimally invasive pathway to better understand her condition.
Does that make sense?
Scott 🙂
