Definition

Pathophysiology

• Predisposing pathology is gross and/or microscopic benign prostatic hypertrophy, which occurs under the influence of dihydrotestosterone in more than 80% of intact male dogs >5 years of age.
• BPH is characterized by large, irregularly shaped, well-vascularized prostatic alveoli and branching infoldings of epithelium with microcysts containing sanguineous prostatic fluid; if infected, these can become abscesses.
• Infection of the hypertrophied canine prostate develops most commonly from ascent of normal urethral flora-rarely from blood-borne bacteria and/or from penetrating wounds introducing bacteria or fungi to the scrotum. The prostate of intact male dogs constantly secretes prostatic fluid, which is deposited into the prostatic urethra and then flows both into the urinary bladder and out the tip of the penile urethra. With prostatitis, prostatic fluid containing blood, inflammatory exudate, and bacteria or fungi is deposited into the urinary bladder and discharged intermittently from the tip of the penis.

Systems Affected

• Gastrointestinal-tenesmus if the enlarged prostate compresses the rectum.
• Hemic/Lymphatic/Immune-mature or immature neutrophilia in acute prostatitis.
• Polysystemic-septic shock if prostatic abscesses rupture, tachycardia, poor tissue perfusion, elevated temperature, and focal or generalized peritonitis.
• Urinary-dysuria if the enlarged prostate compresses the urethra; deposition of prostatic fluid with inflammatory exudate into the urinary bladder.
• Reproductive-pain at copulation and reduction in libido; infertility from infected prostatic fluid in the ejaculate.

Incidence/Prevalence

High in intact male dogs more than 5 years of age. Infection is reported in 40% of dogs with prostatic disease.

Signalment

Signs

Causes

• Infection of the hypertrophied prostate with ascending urethral flora, including Escherichia coli, Staphylococcus spp., Streptococcus spp., Proteus mirabilis, Klebsiella spp., Enterobacter spp., Hemophilus spp., Pseudomonas spp., Pasteurella spp., anaerobic bacteria, and Mycoplasma (most common).
• Infection of the hypertrophied prostate with systemic bacterial infection, including Brucella canis.
• Systemic or local puncture wound infection with Blastomyces dermatitidis.

Risk Factors

• Increasing age
• Presence of functional testes in affected dogs
• BPH and, less commonly, prostatic neoplasia
• Historical androgen or estrogen administration
• Impaired host defense mechanisms

Differential Diagnosis

• BPH without infection, distinguished by semen culture
• Prostatic cysts, distinguished by ultrasound and semen culture
• Prostatic neoplasia, distinguished by ultrasound and tissue biopsy
• Abdominal mass or abscess, distinguished by abdominal imaging

CBC/Biochemistry/Urinalysis

• CBC abnormalities in acute prostatitis and abscessation include immature neutrophilia and toxic neutrophils; immature neutropenia may occur with sepsis. Most dogs with chronic prostatitis have a normal CBC.
• Serum chemistry abnormalities are variable with acute prostatitis. Most dogs with chronic prostatitis have normal serum chemistries.
• Urinalysis abnormalities include hematuria, purulent exudate, and causative microbes; these abnormalities arise, not from primary UTI, but from deposition of infected prostatic fluid into the urinary bladder.

Other Laboratory Tests

• Gross examination, cytology, and culture of whole semen or the prostatic fluid (third) fraction of semen or fluid collected at prostatic massage yields inflammatory exudate with aerobic bacteria, anaerobic bacteria, Mycoplasma, or fungi. Normal prostatic fluid should contain fewer than 100,000 colony-forming bacterial units per mL, and fewer than 5 leukocytes per high power field following fluid centrifugation.
• Although infection with Brucella canis is uncommon, because of the zoonotic potential of this infection, B. canis serology is recommended in all dogs with suspected prostatitis, with follow-up culture of semen for B. canis if serology is positive.

Imaging

Survey radiography of the caudal abdomen, retrograde urethrocystography, and prostatic ultrasonography are indicated to evaluate prostatic size, echo-texture, and detection of cavitating prostatic lesions. The prostate is enlarged if its greatest craniocaudal diameter measured on a line parallel to the line connecting the sacral promontory to the anterior aspect of the pubis on a lateral radiograph exceeds 70% of the length of the distance between the sacral promontory and the anterior aspect of the pubis.

Diagnostic Procedures

• Collection and evaluation of prostatic fluid in seminal plasma and collection of prostatic fluid by prostatic massage in dogs reluctant to ejaculate.
• Ultrasound-directed percutaneous fine-needle aspirate of the prostate.

Pathologic Findings

• Gross pathology of the infected prostate includes enlargement, variable loss of symmetry of the dorsal median raphe, and variable presence of fluid-filled abscesses within or on the surface of the gland. Enlargement may be focal, multifocal, or diffuse.
• Bacterial or fungal infection causes suppurative (bacterial) or granulomatous (fungal) inflammation of the gland. Inflammatory lesions may be focal, multifocal, or diffuse. Abscesses contain accumulations of purulent fluid exudate.
• Biopsy of the infected prostate is not recommended because biopsy may result in the spread of infection to adjacent tissues.

Appropriate Health Care

• Acute prostatitis, prostatic abscess, and rupture of prostatic abscesses into the peritoneal cavity are potentially life-threatening emergencies that can lead to septic shock and death. Hospitalize affected patients and collect diagnostic samples (blood, urine, semen, imaging) immediately.
• Chronic prostatitis patients may be seen as outpatients for diagnostic procedures and started on specific therapy when laboratory results are available.

Nursing Care

• Dogs with acute prostatitis or prostatic abscess should receive antimicrobial drugs intravenously.
• If abscess rupture and peritonitis is suspected, administer intravenous fluid therapy for septic shock.

Activity

Breeding should be avoided until bacteria have been cleared from the prostatic fluid.

Client Education

• Castration is recommended for dogs with acute prostatitis and/or prostatic abscess, as castration induces permanent prostatic involution.
• If maintenance of breeding potential is necessary, long-term or intermittent treatment with finasteride is recommended to induce prostatic involution; routine rechecks at 2- to 3-month intervals for semen culture, semen cytology, and prostatic imaging are recommended. BPH recurs over time in intact male dogs after treatment with finasteride is discontinued, and BPH increases risk of recurrence of prostatitis.

Surgical Considerations

• Surgical management of prostatic abscesses should be deferred until after initiation of antimicrobial therapy and prostatic involution; involution is associated with resolution of abscesses, often making surgery unnecessary.
• Castration is recommended for induction of prostatic involution in non-breeding dogs with prostatitis; castration should be deferred until after identification and treatment (for at least 1 week) of the causative bacterial/fungal agent; alternatively, medical involution of the prostate may be induced with finasteride.
• Placement of Penrose drains, marsupialization, partial prostatectomy, and use of an ultrasonic surgical aspirator have been advocated for treatment of prostatic abscesses in dogs; however, these procedures have been associated with a high percentage of short- and long-term adverse sequelae, including recurrence of abscesses. Surgical drainage with subsequent packing of the cavity with omentum has been associated with the fewest adverse sequelae among surgical treatments.

Drug(s)

Contraindications

Estrogens and androgens cause squamous metaplasia of the prostate and BPH, respectively.

Precautions

Long-term therapy with trimethoprim may lead to keratoconjunctivitis sicca and/or hypothyroidism.

Patient Monitoring

• Repeated evaluation of semen culture, cytology, and prostatic imaging.
• Intervals between reevaluations vary with severity of signs, presence of an abscess, selection of castration or finasteride therapy for prostatic involution, and use of the dog in a breeding program. Intervals between evaluations range from 1 to 8 weeks, with recheck recommended prior to breeding.
• Continue patient monitoring until the dog has been castrated.

Prevention/Avoidance

Castration is recommended to induce prostatic involution, resolution of BPH, and prevention of recurrent infection.

Possible Complications

• Recurrence of infection if prostatic involution is not induced.
• Surgical drainage of abscesses is associated with many complications, including urinary incontinence, recurrent abscessation, hypoproteinemia, scrotal edema, anemia, sepsis, and shock.

Expected Course and Prognosis

• Prognosis is good to excellent except in the case of rupture of prostatic abscesses into the peritoneal cavity, with resulting peritonitis.
• Castration prevents recurrence and improves prognosis.
• Surgical management of prostatic abscesses is associated with complications and a poorer prognosis than medical/surgical induction of prostatic involution.

Associated Conditions

When prostatic fluid is infected, blood, inflammatory exudate, and microbial organisms may reflux into the urinary bladder, which, if detected in a urine sample collected by cystocentesis, may be misinterpreted as primary UTI.

Zoonotic Potential

Rare. Brucella canis and Blastomyces dermatitidis have been isolated from the urine of dogs with prostatic infection, but human infection from these sources has not been reported.

See Also

• Benign Prostatic Hyperplasia
• Dysuria and Pollakiuria
• Hematuria
• Peritonitis
• Prostatic Cysts
• Shock, Septic

Abbreviations

• BPH = benign prostatic hypertrophy
• DHT = dihydrotestosterone
• UTI = urinary tract infection

Author Carl A. Osborne

Consulting Editor Carl A. Osborne

Acknowledgment The author and editors would like to acknowledge the prior contribution of Margaret V. Root Kustritz.

Client Education Handout Available Online