Prostatomegaly (Enlarged Prostate) in Dogs

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Prostatomegaly is an increase in size of the prostate gland. It is common in the intact male dog, with almost all having the symptom as they age. Neutered male dogs are much less likely to have an enlarged prostate.

The general causes of prostatomegaly include:

  • Benign prostatic hyperplasia (BPH) or cystic hyperplasia. This is the most common cause of prostatomegaly.

  • Squamous metaplasia. This is enlargement of the prostate gland caused by excessive exposure to estrogen.

  • Prostatitis. This is a bacterial infection of the prostate gland.

  • Prostatic abscess. This is a severe form of prostatitis where a pocket of infected fluid develops within the prostate.

  • Paraprostatic cysts. These are large fluid-filled sacs connected to the prostate by a thin stalk.

  • Prostatic neoplasia. Tumors of the prostate gland are all malignant and difficult to treat.

    Prostatomegaly may cause a wide variety of clinical signs. Most animals with prostatomegaly have benign prostatic hyperplasia and are asymptomatic, not showing any clinical signs. However, as the prostate enlarges or clinical disease is present, signs associated with prostatomegaly begin to appear.

    What to Watch For

  • Clear, cloudy, yellow or bloody discharge from the penis
  • Straining to pass stool
  • Passing stool shaped like a ribbon
  • Lethargy
  • Anorexia
  • Weight loss
  • Fever
  • Abdominal discomfort
  • Abdominal distention
  • Straining to urinate
  • Fertility problems in intact male breeding dogs
  • Chronic or recurrent urinary tract (bladder) infections

    Diagnosis

  • History and physical exam, including digital rectal exam
  • Urinalysis
  • Culture and sensitivity of the urine
  • Cytologic (microscopic) evaluation of seminal or prostatic fluid, collected by ejaculate, with culture and sensitivity
  • Prostatic massage and wash for cytology, and culture and sensitivity
  • Abdominal radiographs (X-rays)
  • Abdominal ultrasound with or without prostatic aspiration – inserting a needle and syringe into the tissue and obtaining a small sample for cytologic analysis – or biopsy
  • Clotting profile
  • Complete blood count
  • Biochemical profile
  • Thoracic (chest) radiographs
  • Distention retrograde urethrocystography

    Treatment

    Specific treatment requires a specific diagnosis. General supportive care while a diagnosis is pending might include:

  • Intravenous fluids
  • Intravenous antibiotics
  • Urinary catheterization
  • Analgesic (pain) medication
  • Enemas

    Home Care

    Close follow-up and rechecks are recommended to follow prostatic size. Most animals with enlarged prostates do not require emergency veterinary care. If your pet is ill, has a fever, or is very weak, veterinary care should be sought immediately.

  • Prostatomegaly is a common clinical sign in older intact male dogs. As intact dogs age, testosterone and estrogen levels change, and with time, lead to a prostate gland that gradually enlarges. The prostate cells become larger and more numerous and often will form multiple small cysts throughout the prostatic tissue. This change (BPH) is a normal physiologic response to hormonal changes in the body and usually does not cause any clinical signs.

    With intact male dogs, prostatomegaly is, many times, an incidental finding. Occasionally, if the growth of the prostate is excessive, the symptoms of prostatomegaly will be noted. If a dog is neutered prior to reaching sexual maturity, the usual prostatic growth is inhibited.

    Dogs that have been previously castrated that present with prostatomegaly are at greater risk of having prostatic pathology (disease) than intact dogs with enlarged prostates. Some degree of prostatomegaly might be considered normal in the intact male. A more aggressive diagnostic approach is recommended in the neutered male dog with prostatomegaly since this is not a usual finding.

    The physical examination of the prostate is important in providing useful information regarding the depth of the work-up required in evaluating prostatomegaly. The prostate generally can be palpated (felt) rectally or externally just in front of the dog's pelvis. If the enlarged prostate is painful or asymmetrical, further diagnostics are warranted. Asymmetrical prostates are more commonly associated with prostatic neoplasia or infections. Any history of weight loss or poor general body condition may indicate a more chronic (long term) condition.

    Ill animals with large and painful prostates may have prostatitis or a prostatic abscess and would require more rapid attention. Acute or sudden infections of the prostate can be serious and may even spread systemically, causing septicemia (a blood infection). Rapid diagnosis and treatment will improve the prognosis and minimize the potential of sepsis.

    Dogs that are straining to urinate or defecate should also be treated rapidly, as these animals are usually quite uncomfortable, and delays could lead to other problems. Severe constipation or a urinary obstruction might result, requiring emergency intervention. Fortunately, prostatomegaly is usually not an emergency situation, being a more chronic condition. This enables veterinarians to evaluate the patient carefully and to choose an appropriate diagnostic plan.

    Causes

    The location and anatomy of the prostate is important in understanding the clinical signs associated with prostatomegaly. The prostate is located just behind the urinary bladder and under the colon. The prostate encircles the urethra, which is the tube that carries urine from the bladder through the penis and out of the body, as it exits the bladder.

    The prostate is made up of two symmetrical parts, or lobes, located on either side of the urethra. When the prostate is small it sits within the pelvic canal, but as it increases in size, it moves forward into the abdomen.

    The clinical signs of prostatomegaly vary with the type and severity of the prostatic disease. A urethral discharge is commonly seen with prostatic disease. Since the prostate communicates with the urethra, any increase in prostatic secretions may lead to a noted discharge.

    Infection from prostatitis or a prostatic abscess may lead to a cloudy or purulent or pussy discharge. Bloody discharges may be seen with infections, tumors, or even BPH as an increased blood supply to the prostate may lead to hemorrhage. Clear or yellow discharges may be seen with cystic disease.

    Your dog may also strain when he defecates when the prostate enlarges to the point of putting pressure on the colon and decreasing its functional diameter. The occasional "ribbon-like" appearance to the stools is a result of this compression. The decreased diameter can also result in constipation.

    Paraprostatic cysts and prostatic abscesses are most commonly associated with this sign. The prostate generally enlarges outward, but if there is inward enlargement, pressure on the urethra may cause difficulty in urinating. This is an unusual presentation that generally only occurs with very significant enlargement as seen with paraprostatic cysts or abscesses. If the cysts or abscess is very large, distention of the abdomen may even be noted. Finally, animals with infections or tumors may feel ill, have a loss of appetite or have a more chronic weight loss.

    The most common causes of prostatomegaly include:

  • Benign prostatic hyperplasia. BPH is the most common form of prostatomegaly, with virtually all intact male dog acquiring the condition as they age. It is caused by an increase in number and size of the prostate cells as the intact dog ages and is exposed to normal hormonal influences. It is a benign condition that usually does not cause any clinical signs. The majority of the time this condition is found incidentally on routine physical examination.

  • Prostatitis. Bacterial infection of the prostate gland causes pain in the prostate on palpation, and many times the dog acts ill. A large prostate and a bloody discharge from the penis or blood in the urine are common signs. Prostatitis may be acute (sudden) or chronic (long term).

  • Prostatic abscess. An abscess is a walled off pocket of infection containing white blood cells, bacteria, and cellular debris. Abscesses occasionally form within the prostate gland in cases of chronic prostatic infections. They may get to be quite large and cause compression of both the colon and urethra. Your dog may strain when he defecates or urinates and will probably feel ill.

  • Paraprostatic cyst. These fluid-filled sacs are connected to the prostate by a thin stalk. The cysts may be developmental in origin arising from remnants of fetal tissue that normally degenerates (uterus masculinus). The cyst can also be directly of prostatic origin. Single or multiple cysts may be seen, and they can get very large. Animals usually only feel ill if the cysts become large enough to compress other internal organs.

  • Prostatic neoplasia (cancer). Cancer of the prostate may closely mimic other types of prostatomegaly, but usually dogs with prostatic cancer have an asymmetric enlargement or firm nodules in one of the lobes of the prostate. Animals with prostate cancer also tend to be ill systemically, and have a history of weight loss. Tumors of the prostate are almost always malignant. The most common tumors involving the prostate are adenocarcinoma and transitional cell carcinoma. In contrast to most other types of prostatic disease, prostatic cancer occurs with the same frequency in both intact and neutered dogs. In a neutered male dog with significant prostatomegaly, prostatic neoplasia would be high on the list of potential causes.

  • Squamous metaplasia. Squamous metaplasia is a change in the prostate gland due to elevated blood estrogen levels. The prostate gland generally becomes symmetrically enlarged bilaterally. The main cause of this is an estrogen-producing tumor (Sertoli cell tumor). Long-term oral estrogen supplementation can also cause these changes.

  • A complete history and physical examination is the first step of obtaining an accurate diagnosis. It is very important to note if the dog is neutered or intact, as this will affect the diagnostic plan. A rectal exam is always indicated. Depending on the prostate's size and dog's conformation, the prostate (or part of the prostate) is usually palpable rectally. The size, shape, and texture of the gland are noted.

    Prostatomegaly is much more common in intact older dogs. Many times the enlarged prostate is picked up as an incidental finding on the physical exam. If the prostate is smooth, not painful, symmetrically enlarged and the dog is not showing any clinical signs, the diagnosis of BPH is presumed, and no further work-up is recommended. In dogs neutered at a young age, the symptom of prostatomegaly should be investigated more aggressively.

    The following tests may be indicated in some dogs having prostatomegaly:

  • A urinalysis to detect inflammatory changes or blood in the urine and to evaluate prostatic disease. The urine should be a sterile specimen for accurate interpretation. Animals with prostatitis or abscesses may show signs of infection (increased white blood cells and bacteria) in the urine. Some dogs with chronic intermittent bladder infections have underling prostatitis as the primary cause of the problem. A normal urinalysis does not preclude a diagnosis of prostatic disease.

  • A culture and sensitivity of the urine to determine if a bacterial infection is present. A positive growth of bacteria indicates that a urinary tract infection is present. However, the results are not specific for a prostatic infection as an infection anywhere along the urinary tract (bladder, kidneys or prostate) may give positive results. Additionally, dogs with prostatic infections may not have any bacterial growth on culture as the bacteria may be sequestered deep within the prostate and not be present in the urine at the time of sampling. A bacterial culture and sensitivity needs to be interpreted with caution and should be evaluated in light of the total clinical presentation of the animal.

  • Cytologic (microscopic) evaluation of seminal fluid. Samples are obtained via an ejaculate and the fluid is checked for evidence of infection, blood or tumor cells. The sample, ideally the third fraction of the ejaculate, can also be cultured if indicated. Dogs with BPH have normal seminal fluid with or without blood. This test is not often done, since obtaining a sample may be difficult, especially with an ill, painful or uncooperative patient.

  • A prostatic massage and wash. There are several techniques for obtaining this sample. Briefly, a urinary catheter is passed to the level of the prostatic urethra and the prostate is digitally massaged through the rectum. A sample is obtained by flushing fluid into the area and then aspirating the fluid back through the catheter. The sample is then submitted for cytology and culture. Dogs with BPH have normal results.

  • Abdominal radiographs are very useful in evaluating the abdominal organs and the extent of prostatic enlargement. The general size and shape of the prostate is noted, and the lymph nodes that drain the prostate are evaluated for enlargement. With prostatic enlargement the colon may be pushed upward and compressed, while the bladder may be pushed further into the abdomen. Large circular masses adjacent to the prostate may indicate paraprostatic cysts or a large abscess. If there is poor abdominal contrast in the area of the prostate an abscess, tumor or cyst may be suspected. Abnormal calcification of the prostate is easily visualized radiographically and sometimes correlates with a neoplastic process. Infection can also cause these changes. The bones, especially the lumbar vertebral bodies may show evidence of metastatic spread in cases of prostatic neoplasia.

  • An abdominal ultrasound to evaluate the texture and consistency of the prostate, as well as size and shape. Cysts and abscesses are easily visualized. Changes in texture (echogenicity) can be seen with any type of prostatic disease. Abdominal lymph nodes are observed for enlargement. In order to obtain a more specific diagnosis, an area that is identified as abnormal may be aspirated or biopsied using the ultrasound for guidance.

    Fine needle aspiration is useful in collecting fluid from cysts or obtaining small cell samples from the prostatic tissue. A biopsy provides a core of tissue for histopathology (microscopic examination of tissue), and usually provides more accurate information about the pathology of the prostate, since a larger amount of tissue can be evaluated. The ultrasound appearance of a dog's prostate with BPH generally shows a smooth capsule (covering) with the gland symmetrically enlarged. Small cystic areas may be noted that are usually well defined and have smooth margins. Biopsy is the only way to diagnose BPH definitively, but most times is not performed if the clinical presentation and history are typical.

  • Occasionally a clotting profile is indicated if there is significant bloody discharge from the penis or blood in the urine. Potential clotting abnormalities that might cause blood to be present in the urine include immune mediated thrombocytopenia and rodenticide intoxication. If the prostatomegaly is caused by excessive circulating estrogen, the platelet count might be decreased due to bone marrow suppression by the high estrogen levels. Clotting tests to be considered might include an activated clotting time (ACT), a prothombin time (PT), activated partial thromboplastin time (APTT), platelet count, and possible a von Willebrands (VWF) test.

  • CBC. The CBC is a useful test to run in cases of pathologic prostatomegaly as it evaluates the red and white blood cells. Elevations in total white count can be seen in inflammatory conditions associated with prostatic infection or neoplasia. Anemia, assessed by a low red blood cell count, may be seen in chronic prostatic disorders. The anemia seen in prostatic disease is generally low grade and not severe, unless it is associated with squamous metaplasia and excessive estrogen blood levels. Testicular Sertoli cell tumors are the most common tumor to produce estrogen and cause these changes.

  • Biochemical profile. The biochemical profile evaluates the metabolic status of a variety of organ systems. Since prostatomegaly is a more common occurrence on older animals, it is a useful screening test to rule out other problems and or associated disease. Liver values may be elevated with the spread of prostatic neoplasia or by septicemia. If the prostate or an associated prostatic cyst or abscess were causing a urinary obstruction, the kidney values would be elevated, indicating an emergency situation. Blood sugar and electrolytes are also checked to provide a good overall assessment of the general condition of the patient. In dogs with acute prostatitis, or sepsis, hypoglycemia (a low blood sugar) may be seen.

  • Thoracic radiographs. X-rays of the chest are indicated any time prostatic neoplasia is suspected. Thoracic radiographs may show evidence of tumor spread to the lungs. Unfortunately if prostatic cancer is present, and even if the chest films are clear of visible tumors, there is still a reasonable chance that the cancer has spread.

  • Distention retrograde urethrocystography. Occasionally the abdominal X-rays may provide ambiguous results as to the nature of the prostatomegaly, especially if a large prostatic abscess or paraprostatic cyst is present. Distention retrograde urethrocystography is a technique where dye and air are injected through the urethra and into the bladder. This technique allows the urethral lining to be visualized, and better defines the bladder, prostate and any associated mass lesions that may be present.

  • Treatment of the symptoms might be needed while doing a diagnostic work-up, especially if the problem is severe. The following nonspecific (symptomatic) treatments may be applicable to some, but not all pets with prostatic enlargement. These treatments may reduce severity of symptoms or provide relief for your pet. However, nonspecific therapy is not a substitute for treatment of the underlying disease responsible for your pet's condition.

  • Intravenous fluids. If your pet is very ill, febrile, or dehydrated, intravenous fluid support may be indicated. Fluid therapy maintains tissue perfusion, blood pressure and circulatory status. The animals that usually require fluid support are those with acute diseases, such as acute prostatitis.

  • Intravenous antibiotics. Antibiotics may be necessary once cultures are taken if infection is suspected in the ill animal. In critical or very ill animals with a history and exam suspicious of infection, it is prudent to begin antibiotic therapy prior to receiving final diagnostic results.

  • Urinary bladder catheterization. In cases where the prostate causes compression of the urethra and a urinary obstruction, a catheter should be placed from the urethral orifice at the tip of the penis through the urethra and into the bladder. The goal is to bypass the urethral blockage and allow for the normal flow of urine.

  • Analgesic medications. Prostatic disease, especially acute prostatitis, can be very painful. Providing pain relief while a diagnosis is pending will allow the dog to be more comfortable and to be able to rest. Narcotics and nonsteroidal anti-inflammatory medications are most commonly used.

  • Enema. If the prostatomegaly is severe enough to cause compression of the colon, constipation may result. Giving an enema may relieve the discomfort while diagnostic tests are pending.

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