Causes of Benign Prostatic Hyperplasia
Benign prostatic hyperplasia (BPH) is influenced by sex hormones, especially testosterone, 5-alpha-dihydrotestosterone and estrogen. These hormones are the triggers for formation and growth of new prostate cells, which in turn are responsible for benign enlargement of the prostate gland. In intact (unneutered) male dogs, BPH is also influenced by the natural course of aging. BPH is the most common cause of an enlarged prostate gland in older domestic dogs. This condition is also referred to as prostatomegaly.
BPH typically occurs in two phases, called the glandular phase and the complex phase. The end result is an oversized but symmetrical prostate gland, which sometimes contains small cysts and can potentially become cancerous. The most common type of prostate cancer in dogs is squamous cell carcinoma. Squamous cell carcinoma tends to develop in the prostatic epithelium, which is the lining of the external and internal surfaces of the gland itself.
As the dog’s prostate expands over time, it can eventually press on and even obstruct part of the rectum. The rectum is the terminal end of the colon, also known as the large intestine. Over time, this pressure can lead to constipation, straining and difficulty defecating – a condition referred to as “tenesmus”. BPH can also lead to the formation of unusually flat or ribbon-like stools, as well as fecal impaction and constipation. Moreover, the enlarged prostate can put abnormal pressure on the urethra, which is the “tube” through which urine leaves the urinary bladder and exits the body through the external genitalia. This can cause additional discomfort, pain and an artificial sense of urgency to urinate.
Preventing Enlarged Prostate
Neutering juvenile male dogs will almost always prevent the development of benign prostatic hyperplasia, because castration eliminates the hormonal stimulus for enlargement of prostatic cells and tissues. There is no other reliable way to prevent this condition from developing in aging dogs.
In men, BPH can cause urine retention and difficulty urinating. Dogs with BPH do not seem to have these symptoms, although we cannot be sure. When dogs do appear to develop symptoms of difficulty urinating and abnormal urine retention, the cause is more likely attributable to some form of cancer (neoplasia) than to BPH. Some intact males with benign prostatic hyperplasia develop small cysts within their prostate gland. These cysts can be sites for bacterial infection and can develop into puss-filled abscesses. However, they also can be simply incidental findings with no real medical significance.