Feline Autosomal Dominant Polycystic Kidney Disease

PKD is an autosomal dominant form of polycystic kidney disease has been recognised in Persian cats. Studies by Biller et al (1996) showed that in (affected x affected) cats, 73% of offspring were affected. In (affected x unaffected) crosses, 42% of offspring were affected. There was no sex predilection. The age at which renal failure develops in Persian cats with FADPKD is variable. The average age of onset of renal failure in affected cats is 7 years with a range of 3-10 years. Cats positive for the disease should be identified with a view to eliminating the gene from the population. 

Diagnosis

Ultrasound examination of the kidneys is currently the method of choice for the antemortem diagnosis of  FADPKD.  FADPKD is characterised by a variable number of cysts in the renal cortex and renal medulla. These are seen as circular, anechoic structures with well defined, thin walls with a distinct far wall border and strong acoustic enhancement. However, in some young cats, FADPKD may be demonstrated by a single large cyst in one kidney. Simple, single cysts are rare in cats and the identification of one cyst in one kidney in Persian cats is considered consistent with FADPKD. Knowledge of the FADPKD status of the parents and siblings of a cat with a single cyst in one kidney adds further diagnostic confidence to the FADPKD status of the cat in question. Work is currently under way in the U.S. to determine the incidence of simple renal cysts in non Persian cats.

Ultrasound examinations should be performed with the highest frequency transducer available (at least 7.5 MHz). Examination should include imaging the entire kidney in transverse and longitudinal planes. The cysts should not be confused with the normal medulla of the kidneys, particularly in young cats. The normal medulla is relatively hypoechoic when compared to the renal cortex and does not have acoustic enhancement beyond it.

Biller et al (1996) calculated the sensitivity and specificity of ultrasound for the diagnosis of FADPKD in 62 cats using a 7.5 MHz transducer and ATL Ultramark ultrasound machine. Sensitivity was defined as the number of affected cats positive on ultrasonography, at or younger than a specified age divided by the total number of cats positive for FADPKD on histopathology. Specificity was defined as the number of unaffected cats negative on ultrasonography divided by the total number of cats negative for FADPKD on histopathology. Using these definitions, ultrasonography had a sensitivity of 75% and a specificity of 100% when performed at less than 16 weeks of age and a sensitivity of 91% and a specificity of 100% when performed at greater than 36 weeks of age.

In practice the sensitivity and specificity will be influenced by the operator experience and skill, the type of ultrasound machine and the frequency of the ultrasound transducer that is used.

Current recommendations in the United States are that cats negative at 10 months can be called negative and do not required follow up examination. Whilst this figure relates to Biller’s work it still requires further investigation to ensure its accuracy. Current recommendations at the University of Melbourne are that cats have the final examination at 1 year.

Protocol for the examination

The cat should be appropriately identified from microchip or tattoo.

The cat should be sedated if required and restrained for the examination.

The coat does not always require clipping, particularly if in show condition;  high quality images can be obtained by parting the hair and wetting the skin with alcohol. Ultrasound coupling gel should be applied to the skin.

The kidneys should be identified and examined in transverse and longitudinal planes. The entire kidney should be imaged.

Cysts are identified as circular, anechoic structures with well defined walls and a distinct far wall border. There should be obvious distal enhancement (through transmission) beyond the cyst.

An estimate of cyst numbers should be obtained and the diameter of the largest cyst measured.

The findings should be recorded and a certificate provided for each cat examined.

Cats less than 10 months can be examined, however if negative they should be re-examined when they are 10 months (one year) old.

Certification

A national form of certification needs to be developed to assist Persian cat breeders in identifying positive cats and thus being able to reduce the incidence of FADPKD in the breed. The form should be available to members of AAVDI to provide consistency in recording and certifying FADPKD negative and positive cats. It should be developed along the lines of Dr Billers certificate.

Identification of Animals

The certificate should record the coat and eye colour of the cat examined and the microchip number.

Breed Information

A register of FADPKD should be maintained by the Persian Cat Society.

Charge to Clients

Currently the charge to clients varies widely throughout Australia. Costs should be formulated to cover the time taken for examination and the cost of equipment used. However, costs should be kept at a reasonable level to assist breeders in their efforts to eliminate the disease. Multiple cats examined in one visit may enable the fee to be lower for the owner.

References

Biller DS, Dibartola SP, Eaton KA, Pfueger S, Wellman ML, and Randin. Inheritance of polycystic kidney disease in Persian cats. Journal of Heredity 1996;87:1-5

Eaton KA, Biller DS, Dibartola SP. Autosomal dominate polycystic kidney disease in Perisan and Persian cross cats. Vet. Pathol. 1997;34:117-12

 

This document was drafted from the input of the following veterinarians -

Drs. Cathy Beck, Karon Hoffmann, Richard Malik and Sue Foster

 

 


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