Short-term and long-term outcome of cats with big kidney-little kidney syndrome under medical management

The “Big Kidney-Little Kidney” (BKLK) syndrome has been firstly introduced in feline medicine in 2011 to describe a significant size asymmetry between the kidneys. At present, BKLK is considered one of the leading causes of acute on chronic kidney disease (ACKD). Although ureteral surgery is usually considered the gold standard, medical management is often attempted as first-line treatment. The present study aimed to retrospectively investigate the possible association between haemato-biochemical findings, ultrasonographic parameters, and survival in cats with ACKD due to BKLK. We included cats referred to the nephrology and urology service of our hospital (2015-2025) for ACKD due to BKLK. Signalment, haemato-biochemical, urinary, ultrasonographic parameters, and survival time were collected. According to survival time, cats were classified as short-term survivors (ST) if they survived <30 days of hospital admission, and long-term survivors (LT) if they lived > 30 days. Statistical analysis was conducted by GraphPad Prism 10 (statistical significance for p<0.05). Overall survival was 120 days (7-2190). Ultrasonographic signs of ureteral obstruction were found in 93% of cats, with unilateral obstruction in 28% of cats and bilateral obstruction in 72% of cats. According to survival, 37 cats (69%) were in the LT group, and 17 cats (31%) were in the ST group. The ST group showed significantly higher values of median urea (p=0.001), creatinine (p=0.002), and phosphate (p=0.01), and a higher number of cats with severe pelvic dilation, compared to the LT group. No significant difference between the two groups was found in terms of cause of obstruction, number of cats with resolution vs failure, unilateral vs bilateral obstruction, or localisation of ureteral dilation. Cats with BKLK under medical management show elevated survival time, also in the case of partial resolution, regardless of the cause and localisation of obstruction. However, the finding of severe pelvic dilation might be a decisive factor to consider surgery.