Prostatitis and prostatic abscesses in the dog

This prostatic disease may affect both intact and castrated male dogs, after the development of an infection. Chronic prostatitis has also been reported in a cat.

PATHOGENESIS

The term prostatitis indicates an inflammatory process of the prostate gland. Prostatitis may be acute or chronic;  true abscesses are instead secondary to infections of prostatic or para-prostatic cysts, or the result of a severe infection with encapsulation of purulent material.

Unlike in humans, in whom non-bacterial prostatitis is 12 times more likely than bacterial prostatitis, in the dog the disease is typically caused by Escherichia Coli._^1,2Many other bacteria can cause this pathology, among which Staphylococcus, Streptococcus, Klebsiella, Mycoplasma or, more rarely, Proteus spp., Pseudomonas, Brucella canis or anaerobic bacteria.

The exact pathogenesis is still unknown: in most cases it is believed that the bacteria infect the prostate by the ascending route, even though dissemination through the blood or the urinary tract, through semen or by rectal flora have been suggested. The causative microorganisms are very often found in the urine of the affected patients._³ Consequent predisposing factors are urethral urolithiasis, neoplasms, traumas or stenosis.

CLINICAL PRESENTATION

Acute prostatitis. Common symptoms of acute prostatitis are symptoms such as fever, depressed sensorium, anorexia, urethral discharge and pain on palpation of the prostate; more rarely there is the presence of vomiting, caused by a localized peritonitis. An acute prostatitis can also be the cause of septicaemia, which is usually accompanied by conspicuous clinical signs; a less typical clinical sign is constipation: in fact, since defecation is painful, some patients may simply avoid evacuating. Moreover, other subjects show a stiff “stilt-like” gait on their hind legs. On palpation, the prostate volume is usually symmetric and normal or increased, as a concomitant benign prostatic hyperplasia may be present.

Prostatic abscess. The presence of prostatic abscesses is manifested by fever, lethargy and caudal abdominal pain; the prostate is enlarged and asymmetric; tenesmus and constipation may be present. Also in this case haemorrhagic or purulent urethral discharge may become evident, sometimes accompanied by dysuria. About 10% of dogs show symptoms referable to septic shock; a ruptured prostatic abscess can result in localized or diffuse peritonitis with abdominal pain and vomiting.

Chronic prostatitis. In the chronic form, clinical signs are often absent; sometimes owners may report a lethargic state of the animal. Regardless of the presence of clinical signs, chronic prostatitis should always be suspected in all male patients with recurrent lower urinary tract infections, haematuria, or with problems related to hypo-/infertility._⁴ Typically, transrectal palpation of the gland does not evoke pain, and the prostate volume is either normal or enlarged (in the presence of a benign prostatic hyperplasia) an increase in texture may indicate the presence of fibrosis and support the diagnosis of chronic prostatitis.

DIAGNOSIS

The diagnosis of suspicion is based on the clinical history and on clinical and laboratory tests (blood count and urinalysis with urine culture). To confirm the diagnosis of prostatic infection a microbiological examination on a sample of prostatic fluid  should be performed, obtained by ejaculation: this said, animals suffering from acute prostatitis or prostatic abscesses often suffer too much pain to ejaculate; furthermore, in these cases the collection of a prostate fluid sample through massage should be avoided, because of the high risk of rupture of the abscesses or the possible spread of septic emboli. In such cases, an ultrasound-guided fine needle aspiration biopsy may be indicated; in all cases, a cultural examination of a urine sample taken by cystocentesis is recommended.

As for prostatic abscesses, a diagnostic ultrasound examination is extremely useful in the assessment of the prostate and in detecting the presence of systemic signs.

TREATMENT

Acute bacterial prostatitis. Antibiotic treatment, continued for 28 days, based on the drug sensitivity identified by urine culture and an antibiogram. In acute prostatitis the blood-prostate barrier is permeable, because of the prostatic inflammation, so any antibiotic can be used. Initially, the antibiotic therapy should be given parenterally, with a support therapy. Once the patient has been stabilized, the therapy can be continued orally, with a different antibiotic that can penetrate into the gland (see below).

Chronic bacterial prostatitis. In chronic prostatitis, the blood-prostate barrier is intact, consequently this form of the disease is more difficult to treat. The blood-prostate barrier prevents the entry of many drugs into the prostate gland, as the pH of the liquid that carries the antibiotic influences the PK of the drug and this is reflected in its state of ionization. This also determines the degree of liposolubility of the drug, indispensable for enabling antibiotic penetration into the prostate parenchyma.

Since the prostatic fluid, in both physiological and pathological conditions, turns out to be weakly acidic, antibiotics that act as weak bases (erythromycin, clindamycin and trimethoprim), will enter into the prostatic fluid and will concentrate better than others antibiotics._^5,6At the same time liposoluble drugs, such as chloramphenicol, macrolides, trimethoprim and fluoroquinolones, will also be able to penetrate into the prostatic fluid. Penicillin, ampicillin, cephalosporins and aminoglycosides are not able, given their low liposolubility, to penetrate the barrier. When selecting an antibiotic it is also worth considering whether the causative microorganism is gram positive or gram negative: in the case of a gram-positive organism, erythromycin, clindamycin and trimethoprim are recommended; in the case of a gram negative organism, trimethoprim and quinolones are recommended. Antibiotic therapy should be continued for at least 6 weeks.

In the presence of a concomitant lower urinary tract infection, a urine culture during therapy may be useful, in order to monitor the effectiveness of the treatment. Once the antibiotic therapy has been completed, an additional urine culture, during the first week, and then one month after discontinuation of the drug, is necessary. A relapse may occur a few months after discontinuation of the antibiotic therapy: in this case the therapy must be resumed and continued for 3 months, suspending it only in the presence of adverse events. Castration is recommended and can be critical in resolving cases of chronic prostatitis. Should the antibiotic therapy and castration fail, the remaining option is a low dose antibiotic therapy and a prostatectomy. However, in this case, it is quite likely that the dog will become incontinent.

Prostatic abscess. In the presence of a prostatic abscess, the therapy is essentially surgery, and the technique of choice is a prostatic intracapsular omentalization. The evaluation of the bladder and urethral function is fundamental: in fact, if the enlargement of the gland leads to a partial urethral obstruction, a hyperdistension of the bladder could result in bladder atony. The use of a urinary catheter may be necessary in order to allow healing of the detrusor muscle, however, the resulting damage may be irreversible. Castration is recommended as an adjunctive therapy. Antibiotic therapy is recommended, based on the same considerations made for chronic prostatitis and possibly modified based on culture exam. The percutaneous, ultrasound-guided drainage of abscesses has proved to be a fast and safe technique._⁷ Notwithstanding the therapy, it is worth recalling that the morbidity and mortality associated with prostatic abscessae are quite high.

MONITORING OF THE PATIENT

Since it is common for an acute prostatitis to become chronic, a careful reassessment of the patient 7 days after discontinuation of antibiotic therapy is required. On this occasion, a microbiological examination of a urine sample and of a prostatic fluid sample should be carried out. In the presence of chronic prostatitis, the urine should be reassessed at 1 week, 1 month and 3 months following discontinuation of antibiotic therapy.  In a patient treated for prostatic abscess, the gland should be checked by palpation and ultrasound on a monthly basis until actual healing can be confirmed.

Suggested readings

1. Ettinger SJ, Feldman EC: “Textbook of Veterinary Internal Medicine, 6^th edn”. Elsevier-Saunders, St. Louis 2005.
2. Couto CG, Nelson WR: “Medicina interna del cane e del gatto”
3. Elservier-Masson, 2010.
4. BSAVA Manual of Canine and Feline Nephrology and Urology Second edition, Edited by Johnathan Elliot and Gregory F. Grauer, 2007.
5. OsborneCA, Finco DR: Canine and feline nephrology and urology. Williams & Wilkins, Philadelphia, 1995

References

1. Barsanti JA, Finco DR.: “Canine bacterial prostatitis.” Vet Clin North Am Small Anim Pract. 1980 Nov;9(4):679-700.
2. Bersanti J, Crowell W, Finco D. et al.: “Induction of chronic bacterial prostatitis in the dog.” J Urol. 1982 Jun;127(6):1215-9.
3. Black GM, Ling GV, Nyland TG, Baker T.:  “Prevalence of prostatic cysts in adult, large-breed dogs.”J Am Anim Hosp Assoc. 1998 Mar-Apr;34(2):177-80.
4. Memon MA.: “Common causes of male dog infertility.”Theriogenology. 2007 Aug;68(3):322-8. Epub 2007 May 23.
5. Madsen PO, Kjaer TB, Baumuller A.: “Prostatic tissue and fluid concentrations of trimethoprim and sulfamethoxazole: exprerimental and clinical studies.” Urology. 1976 Aug;8(2):129-32.
6. Fair WR, Cordonnier JJ.: “The pH of prostatic fluid: a reappraisal and therapeutic implication.” J Urol. 1978 Dec;120(6):695-8.
7. Bussadori C, Bigliardi E, D’Agnolo G, Borgarelli M, Santilli RA.: “The percutaneous frainage of prostatic abscesses in the dog.” Radiol Med. 1999 Nov;98(5):391-4.