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Canine Benign Prostatic Hyperplasia

Introduction

Benign prostatic hyperplasia (BPH) involves the formation of nodules on the prostate that compress the urethral canal. BPH is a natural consequence of aging that affects older dogs. Entire male dogs (i.e. not castrated) over the age of 5 have an 80% chance of suffering from BPH to some extent.

Fortunately, BPH is not a fatal or threatening condition and is easily treated; yet due to the lack of clinical signs in the majority of cases, BPH can often go undetected. This can cause discomfort for the patient. Whilst there may not be any direct risk posed by BPH, it has been suggested that it may dispose the patient to increased risk of urinary tract infections.

BPH can result in painful urination, frequent urination or hesitancy to urinate; yet these symptoms may not be immediately obvious. Because of the ease at which BPH can be treated and the high prevalence rate in elder males it is worth asking for a screening from your vet if your dog is in the ‘at risk’ category (non-castrated males over the age of five).

The Canine Prostate

The canine prostate and the diseases that affect it are comparable to the human prostate. As such, it has been subject to numerous studies.

The prostate is the only major accessory sex gland in the male dog – an accessory gland being any organ other than the gonads that contribute to sexual function. The prostate is located entirely within the pelvic cavity of a young dog, however as the male ages, the prostate adopts a more abdominal position. As the male ages, the size of the prostate increase, further contributing to the relocation of the prostate.

The canine prostate secretes a fluid that makes up a major part of the male ejaculate; this fluid facilitates sperm transportation by reducing the viscosity of the ejaculate. Due to the acidic nature of this fluid, it is also suggested that it reduces the likelihood of urinary tract infections developing. The acidic environment will make the urinary tract less hospitable to bacteria.

Growth of the canine prostate is influenced by the release of testosterone. The continued release is believed to be responsible for the spontaneous enlargement of the prostate associated with BPH.

Diseases of the Prostate

Benign Prostatic Hyperplasia

The most common canine prostatic disease, BPH, arises spontaneously as a consequence of ageing and endocrine influence. Testosterone (produced by the testes) is converted by the enzyme 5-α reductase to dihydrotestosterone (DHT) in prostatic epithelial cells. DHT is believed to be the predominant factor in promoting BPH.

BPH can be permanently prevented by castration due to the reduction in testosterone production.

Squamous Metaplasia 

Squamous metaplasia is the abnormal change in tissue whereby the epithelial cells become squamous (flattened). Whilst squamous metaplasia doesn’t signify disease, it does show that the body may be experiencing stress or suffering from an irritation.

However, squamous metaplasia may lead to the development of cysts or abscesses that can obstruct the urethra. This can be detected by an increased number of squamous cells in prostatic fluids. The lesion is reversible but usually involves castration.

Neoplasia

Primary neoplasia contributes for around 5% of all canine prostatic diseases. Neoplasia is new, abnormal tissue growth – with prostatic adenocarcinoma (PAC or prostate cancer) being the most common form of neoplasia.

Neoplastic growths on the prostate gland are typically enlarged asymmetries that can put pressure on surrounding organs. Unfortunately PAC can be difficult to diagnose early, meaning treatment often lacks efficacy.

Prostatic Cysts

Cysts can arise either as small-yet-multiple nodules within or around the prostate or as larger, single ‘true cysts’ that are fluid filled and have a distinct cavity wall. Cystic prostate glands will feel enlarged and asymmetrical upon palpation, however many cases show no clinical signs. Larger cysts can prove quite stressful, putting pressure on abdominal organs and posing the risk of infection.

Treatment usually involves draining the cyst, removal of the cystic tissue or in more severe cases – removal of part or the entire prostate.

Prostatitis

Prostatitis is the inflammation of the tissue of the prostate gland. As the body attempts to fight off infection, irritation of the surrounding tissue is likely. Inflammation of the prostate is typically caused by bacteria and can prove painful for the patient. Treatment involves the administration of antibiotics.

Clinical Signs of Canine Benign Prostatic Hyperplasia

The main pathology of BPH is the enlargement of the prostate. This enlargement puts pressure on neighbouring organs and the urethral tract resulting in a number of possible clinical signs:

  • Pain induced lameness
  • Difficulty in defaecation or urination
  • Abdominal pain
  • Haemorrhagic discharge from the urethra
  • Ribbon-like faeces

However it is more likely is that the dog will display no clinical signs of BPH – adding to the argument that dogs in the ‘at risk’ category should be screened with or without display of clinical signs.

A dog displaying BPH induced lameness may be incorrectly diagnosed with orthopaedic disorders particularly of the hips or spine.

Screening for Canine Benign Prostatic Hyperplasia

When presented with a patient believed to be suffering from BPH, the traditional method of diagnosis is rectal palpation. This allows the size of the prostate to be determined. Dogs suffering from BPH will be suffering from an enlarged yet symmetrical prostate that can be detected by palpation.

The problem with rectal palpation is that diagnosis is subjective i.e. dependent on the experience of the person performing the palpation. The experience can also prove uncomfortable for the patient.

A less invasive method of screening for BPH is the use of ELISA tests. Blood is taken from the patient, which is then subject to an ELISA test. ELISA tests are able to detect specific enzymes or proteins in a sample fluid.

The BPH specific ELISA detects levels of the canine prostate-specific arginine esterase, an enzyme whose concentration can be linked to the size of the prostate. A high level of arginine esterase is a strong indicator of BPH.

The ease at which an ELISA test can be run for BPH gives confidence that it could be easily incorporated in to routine blood tests (such as those performed on elderly patients for liver disease or chronic renal failure). This would allow diagnosis of BPH in patients where clinical signs were not apparent.

A positive diagnosis of BPH should be followed up with ultrasound. Ultrasound can quickly and easily confirm a diagnosis – an enlarged, symmetrical prostate can be located easily and will appear clearly on the monitor. The prostate will not appear homogenous and vary in density. Whilst examining the prostate via ultrasound, it is also easy to detect for secondary abscesses or cysts.

Treatment of Canine Benign Prostatic Hyperplasia

Because enlargement of the prostate is almost entirely dependent on the production of high testosterone levels, castration can provide permanent relief from BPH.

Another traditional treatment involves the use of progestagens, which are hormones, produced predominately by the female – large amounts of progestagens are released by the corpus luteum. Progestagens decrease the level of luteinizing hormone which has an antiandrogenic effect on the male i.e. it reduces the amount of androgens in the body which are the hormones responsible for the development of the male sex organs.

There may be cases where castration is not an option, in which case the use of pharmaceuticals is recommended. There are two main pharmaceutical treatments that can be used to rapidly reduce the size of the prostate – osaterone acetate and finasteride.

Finasteride blocks the action of the enzyme 5- α testosterone reductase thus reducing levels of DHT – the compound primary responsible for enlargement of the prostate. Finasteride does not reduce semen quality, libido or fertility – but if the administration of the drug is discontinued, the prostatic hypertrophy (BPH) will return.

Osaterone acetate provides a more rapid reduction in prostate size (40% reduction in 2 weeks). The drug works by blocking the effects of testosterone in the prostate, leaving blood testosterone levels unchanged. The advantage of this is there is no reduction in reproductive quality.

The use of osaterone acetate can be combined with castration to provide rapid and permanent relief from BPH.

 

Veterinary Nursing Journal Vol 26 pp388-399

O’shea, J. D. (1962) Studies on the canine prostate gland: factors influencing its size and weight. J. Comp. Pathol 72: 321-331

Johnston, S. D. Kamolpatana, K. Root-Kustritz, M. V. and Johnston G. R. (2000) Prostatic Disorders in the Dog Anim. Reprod. Sci. 60-61: 405-415

The canine prostate gland: Part 1 Non-inflammatory diseases, Nicola M A Parry BSc MSc BVSc MRCVS

 

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