Benign prostatic hyperplasia (BPH) is a natural consequence of ageing thought to affect over 80 per cent of entire male dogs over the age of five.1 The rate of detection is low, possibly as a result of poor awareness amongst owners and because clinical signs can be vague or, indeed, absent. However, BPH can be a painful condition which is relatively easy to diagnose and treat. It is perhaps a disease which should be given greater consideration when we are presented with elderly entire male dogs.

The canine prostate

The prostate is the only major accessory sex gland in the dog. In younger dogs, it lies entirely within the pelvic cavity but, in adult dogs, it increases in size and occupies an abdominal position. Fluid secreted by the prostate is responsible for more than 90 per cent of the total volume of the canine ejaculate.2 Its main function is to facilitate sperm transport by decreasing the viscosity of the ejaculate, but its acidic nature is also thought to help prevent ascending urinary tract infections.

Disease of the prostate

Benign prostatic hyperplasia is the most common condition of the canine prostate. As the dog ages, the gland undergoes spontaneous enlargement under the continual influence of testosterone. The condition is only seen in uncastrated male dogs and, though more common in elderly animals, can occur from the age of one or two years. Other conditions of the prostate are less common but include prostatic cysts, abscesses, prostatitis and prostatic neoplasia.

Clinical signs of BPH

As the enlarged prostate pushes on neighbouring organs, BPH may present with a variety of clinical signs, including:

•   difficulty in defaecation or urination

•   ribbon-like faeces

•   abdominal pain

•   haematuria or haemorrhagic urethral discharge.

Often the animal presents with lameness resulting from pain in the caudal abdomen, which can be misinterpreted as an orthopaedic disorder of the hips or lower spine. Even more commonly, the dog will show no obvious clinical signs but, because its prevalence is so high, it is well worth screening any entire male dog over the age of five for BPH.

Screening and the role of the VN

Traditionally BPH has been detected by rectal palpation, which gives the clinician an impression of prostate size. In BPH, the prostate is enlarged but symmetrical. The problem with rectal palpation is that, aside from being uncomfortable for the patient, it is subjective and can be inaccurate even in experienced hands. It is also impossible in very large or small breeds.

More recently, a blood test to detect BPH has become available through clinical laboratories in the UK. Odelis CPSE is an ELISA test for canine prostate-specific arginine esterase (a protein similar to prostate-specific antigen in man), which has been shown to be an excellent indicator of prostate size in the dog. This test could be incorporated into geriatric nurse clinics where bloods are also taken to detect for other diseases of the elderly patient, such as chronic renal failure and liver disease.

Diagnosis and workup

In a dog with clinical signs or where rectal palpation or Odelis CPSE has indicated disease, further work-up should include abdominal palpation and, especially, imaging.

Ultrasound examination is particularly useful. In simple BPH, a symmetrically enlarged prostate with loss of the normal homogenous appearance will be seen. It can also be used to reveal other abnormalities, such as prostatic cysts or abscesses, and ultrasound-guided biopsy can confirm diagnosis.

Treatment of BPH

Since the enlarged prostate is dependent on testosterone, traditional treatment has involved removing the testosterone, either through the use of surgical castration or the administration of progestagens, which decrease testosterone through negative feedback on the hypothalamic-pituitary- gonadal axis.

More recently, osaterone acetate (Ypozane, Virbac) has become available, which works by blocking the effects of testosterone on the prostate, shrinking it by as much as 27 per cent in a week and 40 per cent in two weeks. One advantage of this therapy is that blood testosterone remains at normal levels, leaving reproductive potential unaffected. It can also be particularly useful where surgery is contraindicated in elderly dogs because of concurrent disease.

One advantage of castration is that it is permanent: BPH will not recur. A disadvantage is that it can take weeks for blood testosterone levels to fall and, therefore, for the prostate to shrink. However, osaterone acetate can be administered at the same time as surgery so that the dog benefits from rapid resolution of symptoms. 

Canine Prostate Awareness Month is running during November 2011.

This is an initiative to increase awareness of this common condition. For further information, speak to your Virbac territory manager or call 01359 243243.

Author

Chris Geddes MA VetMB MRCVS

References

1.   O'SHEA. J 0 (1962) Studies on the canine prostate gland: factors influencing its size and weight J. Comp. Pathol 72: 321-331.

2.   JOHNSTON. S. 0.. KAMOLPATANA. K.. ROOT-KUSTRITZ. M. V. and JOHNSTON. G. R. (2000) Prostatic disorders in the dog. Anim Reprod. Sci. 60-61: 405-415.

Veterinary Nursing Journal• VOL 26 • November 2011 •