Guerra JM, Freitas MF, Daniel AG, Pellegrino A, Cardoso NC, et al. Age-based ultrasonographic criteria for diagnosis of autosomal dominant polycystic kidney disease in Persian cats. J Feline Med Surg. 2018 Apr 1;:1098612X18764591. PubMed PMID: 29652208.
Autosomal dominant polycystic kidney disease (PKD) is a disorder most often seen in Persians and related breeds, where is may affect 25-50% of cats. It is characterized by the formation of multiple cysts within the kidneys (and less commonly the liver). Cysts are progressive, and generally become larger and more numerous over the course of a cats life. While some cats remain subclinical, others develop early onset kidney failure.
PKD may be diagnosed in cats by use of genetic testing to identify a single base pair substitution in the PKD1 gene. However, testing is often expensive, requires carefully collected DNA samples, and must be shipped to one of only a few reference labs worldwide. Ultrasound exam of the kidneys is readily available, non-invasive, inexpensive, and with a fast turnaround. Many cats, however, have incidental cysts in the kidneys that are benign and non-progressive.
The purpose of this study was to determine if ultrasonographic criteria can be established to consistently diagnose PKD in Persian cats. The study was designed as a prospective observational study.
Eighty-two cats from 33 pedigrees were recruited into the study. Cats received a physical exam, routine biochemistry with thyroxine level, urinalysis, CBC, abdominal ultrasound, and genotype analysis. Genetic analysis was performed on whole blood to identify the presence or absence of a C→A transversion at position 3284 of exon 29 in the feline PKD1 gene, which is considered diagnostic for autosomal dominant PKD.
Twelve cats (14.6%) were positive for PKD on genetic analysis. No difference in age or sex was found between positive and negative cats. 33% of pedigrees were affected.
All PKD positive cats had renal cysts observable on ultrasound. Affected cats had longer kidneys with increased cortical echogeneicity, irregular contour, and corticomedullary blurring compared to non affected cats. 33% of affected cats had liver cysts as well. No cysts were present in unaffected cats.
ROC curve analysis and linear regression were performed on the data to produce a set of cut-off values for diagnosis of PKD in cats based on age of the animals and number of cysts (between both kidneys). Cut off values were;
- ⩽ 15 months = ⩾1 cysts
- 16-32m = ⩾2 cysts
- 33-49m = ⩾3 cysts
- 50-66m = ⩾4 cysts
The overall cut-off value for diagnosis of PKD at any age was 3 cysts in one or both kidneys. The best cut-off for age was 66 months (5.5 years).
There were no significant urine or blood analysis differences between groups, with the exception of a higher blood calcium level in PKD cats.
Some limitations to the study existed. None of the cats evaluated had renal dysfunction, and the presence of kidney disease may have changed the appearance of the kidneys. The only breed assessed was Persian, and so while results may be extended to other breeds of cat, this should be done with caution.
The authors conclude that the diagnosis of PKD in Persian cats may be done with ultrasound with a high degree of accuracy when accounting for age and the number of cysts. They did not have an explanation for the elevated calcium in affected cats. (MRK)