Canine benign prostatic hyperplasia

The prostate is found in all male dogs, with its main function to produce prostatic fluid as a transport and support media for sperm during ejaculation¹.

As male dogs get older, the influence of testosterone (more specifically 5-alpha-dihydrotestosterone [DHT]) causes an increase in epithelial cell numbers (hyperplasia) and an increase in epithelial cell size (hypertrophy). This growth process begins as glandular hyperplasia in dogs as young as 2.5 years of age².

As the dog continues to age, the incidence of benign prostatic hyperplasia (BPH) also increases. Prevalence of BPH is 80% in dogs older than 6 years of age and 95% in dogs older than 9 years of age³.

As dogs age, DHT production continues and the rate of production of prostatic cells and volume exceeds the rate at which new cells are needed. This leads to an overall increase in prostatic volume and an increased size of the prostate⁴.

BPH usually progresses as symmetrical prostatic enlargement growing outward, away from the urethra, due to both hyperplastic and hypertrophic processes⁵. A hyperplastic prostate is extremely well vascularised and, therefore, easily bleeds, which correlates to some of the most common clinical signs of BPH being blood in urine or ejaculate.

More painful diseases such as prostatitis or abscessation are likely consequences of presence of blood in the prostate⁶.

Diagnosis

Diagnosis is usually based on clinical signs such as bloody penile discharge, difficulties in urination or defecation, ribbon shaped faeces, infertility, physical exam and an ultrasound exam (increase in prostatic size and presence of cysts).

Dogs with BPH are frequently considered clinically normal until further investigations are pursued; usually, a rectal exam identifies a non-painful and symmetrically enlarged prostate. No alteration of haematological or biochemical parameters are observed in dogs with BPH⁷.

The diagnosis of BPH can be hard to differentiate from other prostatic disorders such as prostatitis, cysts and adenocarcinomas, because of the similar clinical signs. However, a marker of prostatic activity and secretion is canine prostate-specific arginine esterase (CPSE)⁸.

‘As dogs age, 5-alpha-dihydrotestosterone production continues and the rate of production of prostatic cells and volume exceeds the rate at which new cells are needed. This leads to an overall increase in prostatic volume and an increased size of the prostate.’

CPSE constitutes more than 90% of the seminal protein secretion, with elevated levels being associated with prostatic hyperplasia.

Further research is needed to identify the exact role of CPSE and its uses in diagnosis of non-neoplastic prostatic disorders.

Canine BPH treatment

The removal of androgens is the primary treatment for BPH, which can be performed via castration or administration of medications such as osaterone acetate, sold under the brand name Ypozane (Virbac).

It is the first anti-androgen therapy developed specifically for the treatment of BPH in dogs, and is a steroidal anti-androgen competing directly with androgen receptors at a cellular level in the target organ.

There is a specific inhibitory action on prostatic stroma and the main metabolite of Ypozane (15β-hydroxylated – osaterone acetate) has anti-androgenic activity. It competitively prevents the binding of androgens to their prostatic receptors and blocks transport of testosterone into the prostate⁹.

Ypozane has been shown to shrink the volume of the prostate by 27% after only one week, and by 40% after only two weeks from the start of treatment, with virtually total clinical resolution within this time¹⁰. Because of this rapid resolution, it is often used in dogs that are castrated, as well as sole treatment in entire dogs, with a repeated course every six months.

Ypozane is an oral medication given once daily for seven consecutive days. It is slowly metabolised by the liver with a very long half-life. For this reason, a seven-day course of treatment allows for a pharmacological concentration of the drug to last for six months with minimal side effects and no compromise on breeding performance or semen quality⁹, meaning it is an attractive option in breeding animals.

Ypozane is a progesterone derivative available in several European countries licensed for BPH.