PROSTATE DISORDERS IN DOGS: SOME OVERLOOKED FACTS

Dr. Pravesh Kumar Dwivedi, Dr. Apoorva Mishra, Dr. Sumit Kumar Patel and Dr. Vandana Sharma

College of Veterinary Science and Animal Husbandry, NDVSU, Jabalpur (M.P.) 482001

INTRODUCTION

The canine prostate is an androgen-dependent, ovoid-shaped, bilobed gland composed of glandular and stromal elements, which encircles the urethra of the male  dog caudal to the neck of the urinary bladder. The prostate contributes fluid to the first     and third fractions of the ejaculate.

Clinical symptoms are transient in the beginning and are difficult to recognize as the patient feels very little discomfort. Late presentation of case is responsible for poor prognosis and is generally merges with digestive, urinary and locomotory disorders.

The canine prostate gland can be affected by several disease processes, which often have overlapping clinical signs, making it difficult to reach the correct diagnosis. Accurate diagnosis of prostatic disease requires a thorough understanding of prostatic anatomy, as well as clinical signs associated with canine prostatic disease. Furthermore, knowing which diagnostic tests are indicated, efficient. In addition to standard surgical and medical treatment options for dogs with prostatic disease, there are also new and emerging treatment modalities.

COMMON PROSTATIC DISEASES

There appears to be no breed predilection for prostate disease, large-breed dogs such as German Shepherd dogs and Dobermanns seem to have an increased prevalence,  although a causal relationship has not been established. The common prostatic diseases include: Prostatitis, Prostatic cyst, Prostatic abcessation, Prostatic neoplasia and Benign prostatic hyperplasia (BPH).

Prostatitis

Male dogs generally have sufficient defence mechanisms which protect the prostate from infection. However, when the prostate is compromised by BPH or cysts, prostatitis can occur. In most cases, the prostate is colonized by bacteria that ascend up the urethra, however there is also hematogenous spread. Furthermore, cystitis can extend to the prostate and cause acute prostatitis.

The most common bacterial isolate is Escherichia coli. Other bacteria which are commonly isolated include Mycoplasma, Staphylococcus spp., Streptococcus spp., Klebsiella spp., Proteus mirabilis, Pseudomonas spp. and Brucella canis. The fungal infections like blastomycosis and cryptococcosis are infrequent causes of prostatitis in the dog.

Clinical signs in dogs with acute prostatitis include depression, pain on rectal palpation of the prostate, fever, straining to urinate or defecate, a ‘‘stiff-legged’’ gait, haematuria, oedema of the scrotum, prepuce or hindlimb and polyuria. One, some or all of these signs may be present. In addition, dogs with prostatic abscessation, peritonitis or septicemia may show signs of septic shock. Clinical signs in dogs with chronic prostatitis may be absent or may consist of poor semen quality with infertility or sometimes decreased libido if prostatic contraction is painful. Urine may contain blood, bacteria, leukocytes as with acute prostatitis and dogs with chronic prostatitis may be admitted to a veterinarian for suspected lower urinary tract disease.

A diagnosis is based on the history, physical examination, transrectal examination, diagnostic imaging, haematology, urinalysis, prostatic fluid analysis and bacterial cultures. The prostate will often be very painful on palpation and is typically normal to slightly enlarged. Ultrasonographically, there may be a diffuse increase in prostatic echodensity, which becomes more pronounced over time. Abdominal radiographs may show evidence of prostamegaly or rarely mineralization within the prostate. Urinalysis will typically reveal pyuria and evidence of bacteria. It is important to get a urine sample via cystocentesis whenever possible to make interpretation of culture results more straight forward. Prostatic fluid analysis will reveal numerous neutrophils with the evidence of engulfed bacteria.

Prostatic cyst

Prostatic cysts may be associated with BPH and are formed when canaliculi become obstructed leading to accumulation of prostatic fluid. Cysts are often found in dogs with concurrent BPH or other prostatic pathology. The initial cystic changes are apparently histologically. However, as these cysts begin to communicate with each other and become evident macroscopically, they are termed prostatic cysts. Cysts are classified as either retention cysts or paraprostatic cysts. Retention cysts are cavitating lesions filled with fluid within the parenchyma of the prostate. These cysts typically communicate with the urethra. Paraprostatic cysts are found outside the prostate. These paraprostatic cysts are often very large and can be palpated trans-abdominally.

Prostatic cysts are typically diagnosed via ultrasound evaluation of the prostate. Small cystic structures may not alter the contour of the prostate, making them difficult to detect with trans-rectal palpation or radiology. Very large paraprostatic cysts may be palpable on abdominal palpation, but should be confirmed with ultrasonography.

Prostatic abscess

Prostatic abscessation is a sequel to chronic prostatitis in which cavities of purulent fluid are found within the parenchyma of the prostate. Alternatively, they may develop due to secondary infection of prostatic cysts. Escherichia coli is the most common agent of prostatic infections. Proteus spp, Klebsiella spp, Streptococcus spp, Staphylococcus spp, Pseudomonas spp, Mycoplasma spp and Brucella spp have also been isolated from prostatic abscesses.

The clinical signs often vary, depending on the size of the abscess and whether the infection has become systemic. In dogs with very large prostatic abscesses, there may be signs of tenesmus or dysuria, due to pressure on the colon or urethra. Urethral discharge, whether chronic or intermittent, is a common finding in dogs with prostatic abscesses.

A doughy and asymmetric enlargement of the prostate may be felt on rectal examination. The presence of concurrent urinary tract infection raises the index of suspicion for prostatic abscesses caused by the same organism. The diagnosis is generally made with ultrasonography of the prostate, in conjunction with bacterial culture of prostatic fluid. The cavitating lesions are generally readily visible on routine scanning of the prostate. Palpation typically reveals an enlarged prostate, which may           or may not be painful.

Prostatic Neoplasia

Prostatic neoplasia is the most commonly diagnosed prostatic disorder in castrated dogs, which may have a slightly greater risk of developing prostatic neoplasia than intact dogs. Adenocarcinoma of the prostate and transitional cell carcinomas of the prostatic urethra are the most frequently diagnosed prostatic tumors in dogs. Adenocarcinomas are usually found in 8-10 year old dogs and only sporadically in very young dogs. Castration does not appear to have any protective effect on the canine prostate with regards to neoplasia, with castrates having the same or greater prevalence of prostatic neoplasia when compared to intact dogs. Intact dogs will often also show histological evidence of BPH as well as prostatic neoplasia.

Clinical signs associated with prostatic neoplasia can vary depending on the time of diagnosis, degree of invasiveness and potential metastasis. The most common clinical signs include anorexia, weight loss, hematuria, stranguria, tenesmus and often weakness in the rear limbs. Metastasis to regional lymph nodes and pelvic bones is commonly associated with pain and neurological deficits in the pelvic limbs.

Any time a palpable prostate is found on a transrectal exam in a castrated male, one should be suspicious of prostatic neoplasia in these cases, further diagnostic tests should be performed to rule out neoplasia. Radiographic findings in dogs with prostatic neoplasia can include prostamegaly, prostatic mineralization, regional lymphadenopathy, and evidence of metastasis to the lungs and skeleton. Prostatic tumors present ultrasonographically as solitary or multiple hyperechoic lesions with assymetrically enlarged, irregular margins. The prostate is usually still in the pelvic canal, but in advanced cases, it may be in the abdomen due to its increasing size. Biopsies of the prostate are obtained with the aid of ultrasound or digital guidance. Castrated dogs are more likely to have the poorly differentiated ones.

Benign Prostatic Hyperplasia (BPH)

Benign prostatic hyperplasia is a spontaneous disease of intact male dogs that                                      begins as glandular hyperplasia as early as 3 years of age. It is noteworthy that BPH is a part of an aging process that includes both an increase in cell number (hyperplasia) and an increase in cell size (hypertrophy). Although this condition occurs in both dogs and humans, there are histological differences between species. With time, almost all intact male dogs will develop BPH, with >95% affected by 9 years of age. However, most will not develop clinical signs associated with BPH.

Large breeds such as Dobermann, German Shepherd and Labrador Retriever appear to be predisposed to BPH. Hyperplasia may be glandular or complex. Glandular hyperplasia affects dogs as young as 1 year of age and peaks at 5 to 6 years. There is a uniform proliferation of secretory structures with glandular hyperplasia and gland consistency is normal. Complex hyperplasia is seen in dogs as young as 2 years of age, but predominantly occurs between 8 and 9 years. Cystic dilated alveoli are present with heterogeneous epithelial cells varying from normal to non-functional cuboidal cells. Acini are filled with  eosinophilic material and plasma cells and lymphocytes are present in the hyperplasic  stroma.

Rectal examination indicates a prostate of normal consistency, symmetrical not painful with a discrete or moderate prostatomegaly. Dogs may have tenesmus, hematuria and/or urethral bleeding. Owners may observe ribbon-like stools.

Transrectal digital palpation is the best method of physical examination of the benign prostatic hyperplasia. The prostate is most easily reached when one hand is used to palpate the caudal, ventral abdomen and push the neck of the bladder and prostate into the pelvic canal. Simultaneously the index finger of the other hand is used to perform a digital exam of the caudal aspect of the prostate gland.

Radiographically the prostate appears symmetrically enlarged. The prostate is considered enlarged if it is greater than 70% of the distance between the sacral promontory and the pubis on lateral radiographs. The colon may be displaced dorsally.  On sonography of    hyperplastic prostate, the homogeneous nature of the prostate image is lost and focal to multifocal areas of hyperechoic and/or hypoechoic tissue become apparent.

Differential diagnosis

https://vcahospitals.com/know-your-pet/prostatic-disease-in-dogs

https://www.pashudhanpraharee.com/infertility-in-dogs/

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