Prostatitis

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Introduction

Prostatitis refers to inflammation of the prostate gland, which is usually suppurative and may result in abscesses. Prostatic cysts, neoplasia, benign prostatic hyperplasia and squamous metaplasia can all predispose dogs to developing bacterial prostatitis.

The prostate is constantly exposed to microorganisms that are part of the normal flora in the distal urethra. Inherent protective mechanisms include: retrograde flow of prostatic fluid and urine, the tight prostatic capsule, presence of local immune factors including IgA and antibacterial proteins, and persistent contractile activity emptying prostatic acini.

Development of prostatitis implies a breakdown of these underlying protective mechanisms.

Bacterial prostatitis develops in many intact male dogs with a urinary tract infection, and in recurrent infections the prostate may serve as a residual focus of infection, leading to recolonisation of the urinary tract once antimicrobial treatment is discontinued.

Both acute and chronic prostatitis can develop, but the chronic form is more common.

The most common causative organism is E. coli. The usual range of Gram-positive and Gram-negative microorganisms involved in urinary tract infections can be involved, but Mycoplasmas are more prevalent.

In certain countries, Brucella canis also colonises the prostate, most likely by haematogenous spread.

Clinical Signs

Dogs with acute bacterial prostatitis present with anorexia, vomiting and lethargy. A serosanguinous urethral discharge is often present and dogs may walk with a stiff stilted gait.

Dogs with chronic bacterial prostatitis may only show signs of intermittent serosanguinous urethral discharge between voiding and recurrent urinary tract infections.

Dogs with the acute disease are usually febrile and painful on caudal abdominal palpation.

Diagnosis

On rectal palpation, the prostate is usually enlarged and painful with the acute form, and generally symmetrical.

Haematology may reveal a neutrophilic leukocytosis with a left shift.

Urinalysis shows evidence of a concurrent urinary tract infection with haematuria, pyuria and bacteriuria, and bacterial culture and sensitivity should be performed.

Prostatic aspirates may show neutrophilic infiltrates and bacterial phagocytosis.

On ultrasound examination the prostate may appear hyperechoic.

Systemic signs are absent in chronic prostatitis. On palpation, the prostate may not be enlarged, and the consistency may be variable depending on the amount of fibrosis.

Prostatic fluid contains neutrophils and macrophages.

Culture and histopathology of prostatic tissue enables a definitive diagnosis to be made.

Treatment

Acute prostatitis cases need fluids to treat the dehydration and shock which can occur.

The pH of prostatic fluid is 6.4, so only weak bases and lipid-soluble anti-microbial agents can penetrate the prostate. Appropriate antimicrobials for use include: erythromycin, clindamycin, chloramphenicol, trimethoprim-sulpha and fluoroquinolones.

Antibiotics should ideally be selected according to sensitivity testing, and should be continued for at least 6 weeks, but longer treatment may be necessary.

Follow-up cultures of prostatic fluid can be used to check effective elimination of the infection.

Castration assists in early resolution of prostatitis and should be strongly considered.

Chronic prostatitis can be difficult to treat. Long-term, low-dose treatment can be given for 3-6 months at 50% of the normal dose. Trimethoprim and enrofloxacin have been used in this way.

Prostatic abscesses are best treatment by surgical drainage and omentalisation.


Prostatitis Learning Resources
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Small Animal Emergency and Critical Care Medicine Q&A 10


References

Merck and Co (2008) Merck Veterinary Manual Merial

Schaer, M. (2010) Clinical Medicine of the Dog and Cat Manson Publishing

Bartges, J. (2011) Nephrology and urology of small animals John Wiley and Sons




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