Canine Prostatic Disease Study Guide

Overview and Clinical Importance

Prostatic diseases are common in intact male dogs and represent a significant category of reproductive and urinary pathology on the NAVLE. The prostate gland is the only accessory sex gland in male dogs and is located caudal to the urinary bladder, completely encircling the proximal urethra. Disease of the prostate accounts for 3-10% of intact male dogs presented to veterinary practitioners. The four major prostatic disorders include benign prostatic hyperplasia (BPH), prostatitis, prostatic abscess, and prostatic neoplasia. Understanding the pathophysiology, clinical presentation, diagnosis, and treatment of each condition is essential for board examination success and clinical practice.

Prostate Anatomy and Physiology

The canine prostate gland is a bilobed structure that completely encircles the proximal urethra immediately caudal to the bladder. It is the sole accessory sex organ in male dogs. The gland produces prostatic fluid, a liquid rich in calcium, citric acid, simple sugars, and enzymes that constitutes approximately 25-30% of seminal plasma.

Hormonal Control

Prostate growth and function are androgen-dependent. Testosterone produced by the testes is converted to dihydrotestosterone (DHT) by the enzyme 5-alpha reductase within prostatic epithelial cells. DHT binds to androgen receptors and is the primary hormone controlling prostatic growth, secretory function, and maintenance. Castration leads to prostatic involution due to absence of androgenic stimulation.

Normal Prostate Parameters

Benign Prostatic Hyperplasia (BPH)

Pathophysiology

Benign prostatic hyperplasia (BPH) is the most common prostatic disorder in sexually intact male dogs, diagnosed in almost every intact male dog with sufficient age. BPH involves an increase in both prostatic cell numbers (hyperplasia) and cell size (hypertrophy). The condition results from an altered androgen-to-estrogen ratio with aging, leading to increased sensitivity of prostatic cells to DHT stimulation.

Prevalence by Age

• Glandular hyperplasia begins in some dogs as young as 2.5 years
• After age 4 years, cystic hyperplasia tends to develop
• 80% prevalence in dogs 6 years of age and older
• 95% prevalence in dogs 9 years of age and older

Clinical Signs

Many dogs with BPH are clinically normal or have only mild signs. BPH in dogs differs from humans - the prostate enlarges symmetrically outward (eccentric growth), away from the urethra, so urethral obstruction is rare. When clinical signs occur, they include:

• Hemorrhagic urethral discharge (blood dripping from prepuce unassociated with urination)
• Hemospermia (blood in ejaculate)
• Tenesmus and ribbon-like feces (from dorsal colonic compression)
• Hematuria (usually at end of urination)
• Infertility

Diagnosis

Rectal palpation: Symmetrically enlarged, smooth, non-painful prostate.

Radiography: Prostatomegaly without mineralization. The prostate displaces the colon dorsally and the bladder cranially.

Ultrasound: Diffuse, symmetric enlargement with homogeneous or mildly hyperechoic echotexture. Small fluid-filled cysts (intraparenchymal) may be present in cystic hyperplasia.

CPSE Blood Test: Canine prostate-specific arginine esterase (CPSE) is elevated in BPH. A commercial ELISA test (Odelis CPSE) is available in some countries with high sensitivity (97%) and specificity (92%).

Cytology: Sheets of uniform epithelial cells without inflammation or atypia. May show hemorrhage with mild inflammation without sepsis.

Treatment Options for BPH

Bacterial Prostatitis

Pathophysiology

Prostatitis is the second most common prostatic disease in intact male dogs. It occurs most commonly in intact males 9 years of age and older, though it can affect younger and neutered dogs. Infection typically occurs via ascending urethral bacteria (most common) or hematogenous spread. BPH predisposes to prostatitis because the hyperplastic gland with accumulated prostatic fluid provides excellent media for bacterial growth.

Common Pathogens

• Escherichia coli (most common)
• Staphylococcus species
• Streptococcus species
• Proteus species
• Brucella canis (consider in breeding dogs)

Acute vs. Chronic Prostatitis

Treatment of Prostatitis

Antibiotic selection must consider the blood-prostate barrier. In chronic prostatitis, the intact barrier limits penetration of many antibiotics. Drugs that penetrate best are: highly lipid-soluble, have low protein binding, and are weak bases or amphoteric.

Preferred Antibiotics

• Fluoroquinolones (enrofloxacin, marbofloxacin) - excellent penetration, broad gram-negative coverage
• Trimethoprim-sulfamethoxazole - good penetration, covers common pathogens
• Chloramphenicol - excellent penetration but side effects limit use
• Duration: 4-6 weeks minimum; reculture 2-4 weeks after completing therapy

Prostatic Abscess

Pathophysiology

Prostatic abscessation develops secondary to acute prostatitis or infection of prostatic cysts. When ducts draining the prostate become obstructed, bacteria are trapped and form walled-off pockets of infection. Prostatic abscesses are more severe forms of bacterial prostatitis and should be considered relative emergencies due to risk of rupture, peritonitis, septicemia, and shock.

Clinical Signs

• Similar to acute prostatitis: fever, lethargy, anorexia, vomiting
• Severe caudal abdominal pain
• Tenesmus, dysuria, stranguria
• Purulent or hemorrhagic urethral discharge
• If ruptured: signs of septic peritonitis, shock

Diagnosis

Ultrasound: Definitive diagnosis. Shows fluid-filled cavities within the prostate (hypoechoic to anechoic areas with irregular borders). Cannot always differentiate from sterile cysts - aspiration for cytology and culture is needed.

Radiography: Prostatomegaly, possibly with localized peritonitis (loss of serosal detail) if rupture has occurred. Cannot definitively diagnose abscess.

Treatment

Small abscesses (less than 10 mm diameter): May respond to castration (medical or surgical) combined with antimicrobials, with or without percutaneous ultrasound-guided needle drainage.

Large abscesses: Require surgical drainage via intracapsular prostatic omentalization - the current treatment of choice. This technique involves making bilateral incisions in the prostate capsule, draining abscess contents, digitally breaking down loculations, and packing omentum into the cavities. The omentum provides drainage, increased blood supply, and immune function to promote healing.

Key surgical points: Castration should be performed concurrently or after recovery. Medical castration (with deslorelin or osaterone) may be safer in unstable patients as surgical castration during active infection increases risk of scirrhous spermatic cord formation.

Prostatic Neoplasia

Overview and Epidemiology

Prostatic carcinoma is uncommon (5-7% of prostatic diseases) but highly aggressive. Unlike BPH and prostatitis, prostatic neoplasia is NOT androgen-dependent and occurs with HIGHER incidence in NEUTERED males than intact dogs. This is a critical distinction for NAVLE. The most common tumor types are adenocarcinoma and transitional cell carcinoma (TCC) extending from the urethra.

Risk Factors and Breed Predispositions

• Average age at diagnosis: 10 years
• Neutered males at higher risk than intact males
• Medium to large breed dogs
• Predisposed breeds: Doberman Pinscher, Shetland Sheepdog, Scottish Terrier, Beagle, Miniature Poodle, German Shorthaired Pointer, Airedale Terrier

Clinical Signs

Prostatic carcinoma is locally aggressive with high metastatic rate (70-80% at diagnosis). Clinical signs reflect both local invasion and distant metastasis:

• Urinary signs (62%): Stranguria, dysuria, hematuria, urethral obstruction (more common than with BPH)
• GI signs: Tenesmus, ribbon-like feces, constipation
• Systemic signs (42-70%): Weight loss, anorexia, fever
• Gait abnormalities (36-50%): Pelvic limb weakness, lumbar pain due to vertebral or pelvic metastasis
• Bone pain: Lameness if skeletal metastasis present

Diagnosis

Rectal palpation: Firm, painful, irregular, nodular, and often immobile prostate. May palpate sublumbar lymphadenopathy.

Radiography: Prostatomegaly with MINERALIZATION (multifocal, irregular mineral densities) is highly suggestive of carcinoma. Evaluate for sublumbar lymphadenopathy, lytic or proliferative changes in lumbar vertebrae and pelvis, and pulmonary metastasis.

Ultrasound: Irregularly shaped prostate with heterogeneous, hyperechoic foci (mineralization). Asymmetric enlargement. Loss of normal bilobed architecture.

Cytology/Histopathology: Definitive diagnosis requires biopsy. FNA may not detect malignancy in all cases. Catheter biopsy or ultrasound-guided needle biopsy can be performed. Note: FNA is NOT recommended if TCC is suspected due to risk of tumor seeding.

Treatment and Prognosis

Differential Diagnosis of Prostatic Diseases

Memory Aids for NAVLE Success

The 4 Ps of Prostatic Disease

Proliferation (BPH) - Pus (Prostatitis/Abscess) - Pocket (Cyst) - Proliferative neoplasm (Carcinoma)

BPH Age Prevalence

"6 = 80, 9 = 95" - 80% of dogs at 6 years, 95% at 9 years have BPH

Neutered Dog Neoplasia Rule

"Neutered + Prostate Problem = Neoplasia until proven otherwise" - BPH and prostatitis are rare in neutered dogs; neoplasia is MORE common

Antibiotic Penetration: "FTC"

Fluoroquinolones - TMS (trimethoprim-sulfa) - Chloramphenicol = drugs that cross the blood-prostate barrier