Prostatic Disease in Dogs

By Malcolm Weir, DVM, MSc, MPH; Ryan Llera, BSc, DVM; Ernest Ward, DVM

What is the prostate?

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 clinical 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 can become 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.

Some dogs with prostatic disease will have blood in their urine; however, bloody urine is not specific to prostatic disease, as it is also a sign of other diseases affecting the urinary system. In addition, if the prostate is painful due to a disease process, affected dogs may also show signs of abdominal pain or even an unwillingness to move or walk.

What are the diseases that can affect a dog’s prostate?

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 common estrogen-producing tumor that causes squamous metaplasia.

3. Cystic hyperplasia. This condition is usually secondary to BPH 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 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 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 may arise without any association with hormones.

How is prostatic disease in dogs 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.

"Because there are many diseases of the prostate, it is necessary to perform several tests to determine the exact cause of a 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 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.

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 often obtained by fine-needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the prostate, then placing them on a microscope slide to be examined by a veterinary pathologist. In some cases, results from FNA may not be entirely clear and a biopsy (surgical removal of a tissue sample) may be necessary.

A blood test for canine prostate-specific arginine esterase (CPSE) is also available. CPSE is an indicator of prostatic secretion and can be useful as a screening tool for BPH. Your veterinarian may also run additional blood tests, such as a complete blood count (CBC) and a biochemical panel, to look for disturbances in other organs of the body.

How is prostatic disease in dogs treated?

Treatment depends on the diagnosis and the type of disease affecting your dog.

  • 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 treatments, such as finasteride (Proscar®, Propecia®) and megestrol acetate (Ovaban®, Megace®) 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 the prostate gland, treatment for several weeks to months is usually necessary. Antibiotics that can penetrate the prostate include enrofloxacin (Baytril®), erythromycin (Gallimycin®, Erythro®), clindamycin (Antirobe®, Cleocin®), ciprofloxacin (Cipro®), chloramphenicol (Chloromycetin®, Viceton®), and trimethoprim-sulfonamides (Bactrim®, Septra®), each of which has varying pros and cons. Since prostatic infections are typically secondary to another disease, treating the prostatic infection is only part of the overall treatment 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). Non-steroidal anti-inflammatory drugs (NSAIDs), such as piroxicam (Feldene®) or meloxicam (Metacam®), may be useful in prolonging the dog’s lifespan. The prognosis for prostatic cancer is, however, usually poor.

Additional supportive care may include the NSAIDs mentioned above and stool softeners or laxatives to help prevent constipation. Your veterinarian will advise you about the treatment options most appropriate for your dog's condition.

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