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Prostatic Disease in Dogs

By Ryan Llera, BSc, DVM; Ernest Ward, DVM

Medical Conditions, Pet Services

What is the prostate?dog_m_reproductive_system_prostate_2018-01

The prostate is a small gland located near the neck of the urinary bladder of male dogs. The urethra (the tube that carries urine from the bladder to outside the body) passes through the prostate shortly after leaving the bladder. The purpose of the prostate is to produce some of the fluids found in semen.

 

What are the signs of prostatic disease?

Enlargement of the prostate gland is common with most prostatic diseases. Since the urethra passes through the prostate, enlargement of the gland compresses the urethra and urination becomes difficult and uncomfortable.

Complete urethral obstruction rarely occurs with prostatic problems, but an affected dog will spend a prolonged time urinating and will often produce only a thin stream of urine. If the prostate is very enlarged, the colon, located just above the prostate, may also become compressed, causing difficulty with passing bowel movements. Dogs with prostatic enlargement often have a history of straining to urinate or defecate.

"A dog with prostatic enlargement often has a history of straining to urinate or defecate."

In addition, some dogs with prostatic disease will have blood in the urine; however, bloody urine is not specific for prostatic disease as this is a sign for other diseases affecting the urinary system.

What are the diseases that cause the prostate to enlarge?

There are at least seven diseases affecting the prostate.

  1. Benign prostatic hyperplasia (BPH). This is a non-cancerous enlargement of the prostate gland. It is associated with the male sex hormone testosterone and is the most common disease of the prostate.
  2. Squamous metaplasia. This is a non-cancerous enlargement of the gland caused by excess amounts of the hormone estrogen in male dogs. An estrogen-producing testicular tumor called a Sertoli cell tumor is the most commonly diagnosed estrogen-producing tumor that causes squamous metaplasia.
  3. Cystic hyperplasia. This condition is usually secondary to benign prostatic hyperplasia or squamous metaplasia. It is caused by obstruction of the ducts that carry prostatic secretions to the urethra. This condition causes the development of numerous fluid-filled cavities in the prostate.
  4. Paraprostatic cysts. These are fluid-filled cysts that develop adjacent to the prostate. They are abnormal tissue remnants from embryonic development (before the puppy was born). The cysts begin to develop shortly after birth but often do not cause problems until the dog is several years old.
  5. Bacterial infection. Bacteria may enter and infect the prostate by traveling up the urethra, or may travel down the ureter or urethra from an infection that originates in the kidneys or urinary bladder, respectively. A bacterial infection is usually associated with a pre-existing abnormality of the prostate, such as BPH.
  6. Prostatic abscess. This is a more severe form of a bacterial infection. If the ducts that drain the prostate become obstructed, bacteria are trapped in the prostate and form a walled-off site of infection known as an abscess. Prostatic abscesses can be challenging to treat since many antibiotics are unable to penetrate into the prostate.
  7. Prostatic cancer. This disease is a rare occurrence in dogs. It may be associated with hormones from the testicles, adrenal glands, or pituitary glands or without any association with hormones.

How is prostatic disease diagnosed?

The first step in diagnosis is to determine if the prostate is enlarged. To do this, your veterinarian will attempt to palpate (feel) the prostate either through the abdominal wall or during a rectal exam. Radiographs (X-rays) or an ultrasound examination may be required to diagnose an enlarged prostate gland.

"Several tests will be needed to determine the exact cause of a particular patient's condition"

Because there are many diseases of the prostate, it is necessary to perform several tests to determine the exact cause of a particular patient's condition. These tests may include:

  • culture of the dog's urine to determine if there is a bacterial infection,
  • a microscopic examination of the cells in the urine, and
  • a microscopic examination of the cells in prostatic fluid or in the prostate.

How will my veterinarian get these samples?

A free-flow urine sample iscollected (urine is voided voluntarily by a pet and collected into a container as the pet urinates). Samples of prostatic fluid are obtained by passing a urethral catheter to the level of the prostate and massaging the prostate to milk fluid out of it.

Samples of prostatic cells are obtained by fine needle aspiration (FNA) or biopsy. If the prostate is greatly enlarged, it may be sampled by through the body wall by FNA or biopsied. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the prostate and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope. In some cases, results from FNA may not be entirely clear and biopsy may be necessary.

How is prostate disease treated?

Treatment depends on the diagnosis, and the type of disease that is present.

Diseases associated with excessive hormone levels (BPH, squamous metaplasia, and cystic hyperplasia) are typically treated by neutering the dog. Because testosterone and estrogen are both formed in the testicles, neutering is generally an effective treatment. The prostate will return to its normal size within one month after surgery. Certain medications or hormone replacements, such as finasteride, megestrol acetate, and GnRH, may be used to treat specific prostatic conditions.

Paraprostatic cysts and prostatic abscesses require surgery to drain and remove them.

Diseases involving primary or secondary bacterial infections are treated with aggressive and prolonged antibiotic therapy. Because it is difficult for antibiotics to penetrate into the prostate gland, treatment for several weeks to months is usually necessary. Antibiotics that can penetrate the prostate include enrofloxacin, erythromycin, ciprofloxacin, chlorhamphenicol, doxycycline, and trimethoprim-sulfonamides each having varying pros and cons. Since the prostatic infections are typically secondary to another disease, treating the prostatic infection is only part of the overall treatment.

"Because it is difficult for antibiotics to penetrate into the prostate gland, treatment for several weeks to months is usually necessary."

Primary prostatic cancer in dogs does not respond well to currently available forms of treatment. If the prostatic tumor is associated with an excess of a hormone, neutering may be beneficial. Targeted radiation therapy may be possible, and some chemotherapy drugs may be useful depending on the type of tumor (see handout “Prostate Tumors in Dogs” for more information). The prognosis for prostatic cancer is usually poor.

Additional supportive care may include anti-inflammatory medications such as meloxicam (brand name Metacam®) or piroxicam (brand name Feldene®). Stool softeners or laxatives may be useful to help prevent constipation. Your veterinarian will advise you about the treatment options that are appropriate for your dog's condition.

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