Prostatic Disease in Dogs
What is the prostate?
The prostate (commonly miscalled the "prostrate") 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 markedly enlarged, the colon, located just above the prostate, may also become compressed, causing difficulty in passing bowel movements.
"A dog with prostatic enlargement often has a history of straining to urinate or defecate."
Therefore, 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. Bloody urine is not specific for prostatic disease.
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 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 urethra from an infection that originates in the kidneys or urinary bladder. A bacterial infection is usually associated with a pre-existing abnormality of the prostate, such as benign prostatic hyperplasia.
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 abscess.
7. Prostatic cancer - This disease is much less common in the dog than all of the others. 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 through the rectal wall. Radiographs or an ultrasound examination may be required to diagnose an enlarged prostate gland.
"...necessary to perform several tests 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:
1) culture of the dog's urine to determine if there is a bacterial infection,
2) a microscopic examination of the cells in the urine, and
3) a microscopic examination of the cells in prostatic fluid or in the prostate itself.
How will my veterinarian get these samples?
A "free flow" or voided urine sample is appropriate for investigation of prostatic disease. 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 needle aspiration or biopsy. If the prostate is greatly enlarged, it may be aspirated or biopsied through the body wall; otherwise, an approach through the rectal wall is necessary. An aspiration sample is taken through a very small bore needle and only recovers a few cells. Sometimes this is adequate for analysis; other times it is not. A needle biopsy sample is obtained through a large bore needle, and often this sample is obtained using ultrasound guidance. A biopsy sample recovers a piece of prostatic tissue.
In most cases, these samples will be sent to a laboratory, where a veterinary pathologist will examine them to determine the diagnosis.
How is prostate disease treated?
Treatment depends on the diagnosis, and the type of disease that is present.
1. 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..."
Because it is difficult for antibiotics to penetrate into the prostate gland, treatment for several weeks to months is usually necessary. Since most of the infections are secondary to another disease, treating the prostatic infection is only part of the overall treatment.
2. Diseases associated with excessive hormone levels include benign prostatic hyperplasia (BPH), cystic metaplasia, cystic hyperplasia and testicular tumors.
"...neutering is generally an effective treatment for these conditions."
Since testosterone and estrogen are both formed in the testicles, neutering is generally an effective treatment for these conditions. The prostate will generally return to normal within one month after surgery. Certain medications or hormone replacements may be used to treat specific prostatic conditions.
3. Paraprostatic cysts and prostatic abscesses require major abdominal surgery to drain and remove them.
4. Primary prostatic cancer in dogs does not respond well to any currently used form of treatment. If it is associated with an excess of a hormone, neutering may be beneficial; however, most are not and spread to other parts of the body.
"The prognosis for prostatic cancer is usually poor in the dog."
The prognosis for prostatic cancer is usually poor in the dog. As advances are made in the treatment of human prostate cancer, we expect new treatments and surgeries to become available for dogs suffering from this disease. Your veterinarian will advise you about the treatment options that are appropriate for your dog's condition.