Diseases of the Prostate Gland

Chapter 84 Diseases of the Prostate Gland



Nancy D. Kay


Diseases of the prostate gland are common in middle-aged and older dogs. Medium- and large-breed dogs (especially Doberman pinschers) are more commonly affected. Although cats have prostate glands, for unknown reasons feline prostatic disease is extremely rare. This chapter discusses canine prostatic disease only.



ETIOLOGY


Several types of prostatic disease exist and some may occur simultaneously (e.g., prostatic cyst with abscessation or prostatic neoplasia with bacterial prostatitis).



Benign Prostatic Hyperplasia


To some degree, both hypertrophy (increased size) and hyperplasia (increased numbers) of prostatic cells account for enlargement of the gland in all middle-aged and older non-castrated dogs.




Key Point


Benign prostatic hyperplasia is the most common disorder of the prostate gland.



• Causes of benign prostatic hyperplasia include an imbalance in the ratio of androgens to estrogens, increased numbers of androgen receptors, and increased tissue sensitivity to androgens.

• Dihydrotestosterone is the main androgen that promotes prostatic hyperplasia.


Squamous Metaplasia


This morphologic alteration of prostatic epithelial cells is caused by estrogen stimulation arising from an exogenous or endogenous (e.g., Sertoli cell tumor) source.



Cystic Hyperplasia


This condition refers to multiple fluid-filled cavities within the prostatic parenchyma that result from the obstruction of glandular excretory ducts.


• Cystic hyperplasia commonly is associated with benign prostatic hyperplasia and squamous metaplasia.


Paraprostatic Cyst


These fluid-filled structures develop adjacent to the prostate gland and result from fluid accumulation within embryologic vestiges (uterus masculinus). The cystic lining may become calcified.



Prostatic Infection



• Bacterial prostatitis occurs when normal host resistance is altered.

• Predisposing causes include disruption of normal glandular architecture (benign hyperplasia, squamous metaplasia, neoplasia, parenchymal cysts), urethral diseases, urinary tract infections, alterations in urine flow, altered prostatic secretions, and host immune dysfunction.

• Infection usually occurs by an ascending route, although hematogenous spread of bacteria also may occur.

• The most common pathogens are Escherichia coli, Staphylococcus, Proteus mirabilis, Streptococcus, and Mycoplasma. Less common isolates include Klebsiella, Brucella canis, Pseudomonas, and Ureaplasma. Anaerobic infections are rare.

• In rare cases, disseminated (systemic) mycotic infections, such as Blastomyces, Cryptococcus, or Coccidioides, can cause prostatitis (see Chapter 20).


Idiopathic Prostatitis


Idiopathic (non-bacterial) prostatitis has been documented in dogs.



• Clinical signs are similar to those associated with chronic bacterial prostatitis.

• The etiology of the inflammation is uncertain.


Prostatic Abscess


Prostatic abscesses are either extensions of bacterial prostatitis in which obstruction of an excretory duct has occurred or secondary infection of a preexisting cyst.



Prostatic Neoplasia


Neoplasia is relatively rare compared with other forms of canine prostatic disease.


• Prostatic adenocarcinoma and transitional cell carcinoma are most common.

• Previously, castration was thought to prevent the development of prostatic cancer. In one study, 19 of 43 dogs had been castrated at least 3 years before the development of prostatic disease. More recent studies have also concluded that castration at any age has no sparing effect on the development of prostate cancer. Tumors from neutered dogs tend to be more highly undifferentiated and often metastasize to the lung. This may reflect a more aggressive neoplastic process or delayed detection of the disease.

• Development of prostatic cancer in dogs may not be hormonally mediated or may be influenced by hormones of non-testicular origin. Hormones produced by the adrenal and pituitary glands may play a significant role.

• Metastasis is common. Frequent sites of metastasis include lymph nodes (regional and distant), bones (near and distant), and visceral organs.


CLINICAL SIGNS


Clinical signs associated with canine prostatic disease are variable. Depression, anorexia, and vomiting are systemic manifestations of bacterial prostatitis or prostatic abscessation. Other clinical signs do not correlate well with etiology (Table 84-1). Hematuria and blood dripping from the prepuce are the most frequent signs seen with most types of prostatic disease. In animals with uncomplicated benign prostatic hyperplasia, however, clinical signs frequently are absent until prostatomegaly becomes severe.



Table 84-1 INCIDENCE OF CLINICAL SIGNS ASSOCIATED WITH PROSTATIC DISEASE

image


• Hematuria is caused by reflux of blood from the prostatic urethra into the bladder. It also may be associated with a concurrent bacterial cystitis.

• Urethral discharge results from the exudation of blood, pus, and/or prostatic fluid into the prostatic urethra. This fluid drips passively from the penile urethra and is often blood tinged.

• Stranguria is present if partial or complete urethral obstruction results from prostatic enlargement.

• Fecal tenesmus or a change in stool diameter occurs when prostatic gland enlargement encroaches on the rectum. Constipation may be secondary to avoidance of pain associated with defecation.

• Fever, depression, anorexia, vomiting, and diarrhea are signs of systemic involvement and are most commonly associated with bacterial prostatitis or prostatic abscessation.

• Recurrent urinary tract infection in a male dog may be associated with non-resolving or recurrent bacterial prostatitis.

• Abdominal distention may be caused by a paraprostatic cyst or prostatic abscess.

• Caudal abdominal pain, lumbar pain, and/or hind limb stiffness may be associated with metastasis of prostatic neoplasia to bone or muscle or with peritonitis associated with prostatic abscess.

• Hypertrophic osteopathy may occur secondary to prostatic disease such as tumors.

• Hind limb pitting edema may occur secondary to lymphatic invasion by metastatic tumors.

• Urinary incontinence can be caused by impingement on the pelvic nerves by an adjacent prostatic mass (tumor or abscess) or from inflammation of the urethra from urinary tract infection.

• Other clinical conditions that may be associated with prostatic disease include impaired libido, infertility, sepsis, ketoacidotic diabetes mellitus, perineal hernia, and testicular tumor.


DIAGNOSIS


Localizing and defining the etiology of diseases of the prostate gland can be a challenging task. Until recently, few diagnostic techniques have combined reliability and specificity of results with safety and ease of application. The ideal method for the diagnosis of prostatic disease should localize the disease to the prostate gland and eliminate other parts of the urinary and reproductive tracts as sources of the disease.



Physical Examination


Abdominal palpation in dogs with prostatic disease may reveal abdominal pain, abdominal distention, or the presence of an abdominal mass.




Key Point


A rectal examination is essential in the diagnosis of prostatic disease.



• In rectal examination, palpate ventrally for the prostate gland and dorsally for iliac lymph node enlargement or lumbar pain.

• Evaluate the prostate gland for location, size, symmetry, surface contour, consistency, movability, and pain. The normal prostate gland is bilobed, intrapelvic, symmetric, smooth, movable, and non-painful.

• As the prostate gland enlarges with disease, it may move cranially over the pelvic brim. Therefore, simultaneous rectal and caudal abdominal palpation may be helpful.



Key Point


The prostate gland of a normal Scottish terrier may be up to 4 times larger than those of other breeds.



Imaging Studies



Abdominal Radiography


Abdominal radiography rarely determines the specific etiology of prostatic disease, but it can reveal various associated abnormalities, including the following:



• Prostatomegaly

• Prostate gland asymmetry

• Abnormal fluid-filled mass in the caudal abdomen

• Prostate gland mineralization

• Iliac lymph node enlargement

• Vertebral or pelvic bone periosteal reactions

• Decreased soft tissue detail in the caudal abdomen due to tissue inflammation

• Urine or fecal retention



Key Point


Prostate gland mineralization and iliac lymph node enlargement are often but not always associated with prostatic neoplasia.



Urethrography


Positive-contrast retrograde urethrography may help localize the disease process. However, there is no correlation between the urethroprostatic reflux and the type of prostatic disease. Reflux may be observed in some dogs without prostatic disease.



Ultrasonography


Ultrasonography can be used to evaluate the prostate location, size, and architecture and to guide percutaneous needle aspiration or needle core biopsy. Ultrasound observations may include the following:



• Prostatomegaly

• Intraprostatic cyst or abscess (appears as focally hypoechoic or anechoic)

• Paraprostatic cyst

• Focal or multifocal areas of increased echogenicity (may represent bacterial prostatitis or neoplasia)

• Shadowing (may represent bacterial prostatitis or neoplasia)

• Prostatic calculi

• Iliac lymphadenopathy


Laboratory Studies



Complete Blood Count and Serum Biochemistry



• Hemogram abnormalities do not consistently correlate with the occurrence of infectious or noninfectious prostatic diseases. An exception is neutrophilic leukocytosis, which is consistently associated with acute, fulminant bacterial prostatitis.

• A mild to moderate nonregenerative anemia may occur in chronic inflammatory or neoplastic prostatic disease.

• An increase in serum alkaline phosphatase commonly accompanies bacterial prostatitis and prostatic neoplasia. It is not known which alkaline phosphatase isoenzyme is responsible.


Urinalysis and Urine Culture



• Bacterial cystitis and bacterial prostatitis may occur independently.

• Urinalysis and urine culture are always indicated for animals with signs of urinary tract disease. However, they may not be useful in the diagnosis of prostatic disease.
• For example, urine sediment examination is not reliable for the diagnosis of prostatic neoplasia, and urine cultures can be negative in dogs with bacterial prostatitis or prostatic abscess.

• For this reason, in addition to urine, evaluate prostatic fluid, prostatic tissue, or both in dogs suspected of prostatic disease.


Prostatic Fluid or Tissue Culture


This procedure is necessary for documentation of bacterial prostatitis. Mycoplasma organisms require specialized culture media (pleuropneumonia-like organism [PPLO] agar); therefore, specifically request this culture (see “Specimen Collection” for techniques for collection of microbiology specimens).



Prostatic Fluid Cytology


Cytologic studies may identify benign prostatic hyperplasia, squamous metaplasia, bacterial prostatitis, non-bacterial prostatitis, and prostatic neoplasia (see “Specimen Collection” for techniques for collection of cytology specimens).

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  4. Otitis Media and Otitis Interna

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Diseases of the Prostate Gland

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