THE MALE DOG
Male dogs are much more frequently presented for investigation of infertility or reproductive tract disease of the genitalia than are cats. Most of the pathologies of the male dog are related to prostatic and testicular disease.
Disease processes in the prostate are common and result from various origins such as infectious, hormonal, anatomic or embryologic. An increase in the incidence of those conditions is observed with age and could be related to the physiological
hyper-development of the organ observed under the influence of androgens.
The prostatic secretions whose pH is acid play a role during rest as a bactericidal preventing ascending bladder infections and a major role during ejaculation in the production of the semen. Indeed, in dogs the prostate is largely (more than 90-95%) responsible for the volume of the ejaculate produced.
During the dog's life, the evolution of the prostate could be divided in 3 periods. The first one correspond to the period of embryogenesis and first post-natal development. This phase ends when the animal is around 2 to 3 years. The second one is a phase of exponential hypertrophic development. This phase is clearly androgeno-dependant and terminates approximately when the animal is 12 to 15 year. The last phase is a senile involution phase and follows the previous one when, in the geriatric animals, the production of androgens slowly begins to decrease. The clear distinction between those different periods is difficult to establish and is indeed highly subjective with high variations between animals. However, it is generally accepted that after 5 years, nearly all dogs present a certain degree of prostatic hypertrophy which may continue to develop leading in some animals to the pathological features known as benign prostatic hyperplasia (BPH). This clinical conditions is observed in 60% of the dogs of more than 5 years and in nearly 100 % of more than 10 to 12 years old. The position of the prostate change slowly with the increase of its size. Indeed, from being pelvic in young animals the prostate slowly becomes more abdominal and finally after 8 to 12 years becomes abdominal.
It is beyond the objectives of this text to review all prostatic diseases, clinical signs, investigational methods and treatments. The reader is asked to consult publications given in the reference list below.
The prostate gland may be affected by infection (acute and chronic prostatitis and abscess), endocrine dependant (prostatic hyperplasia and metaplasia) or tumorous processes (adenocarcinoma). Cysts are also described as congenital (paraprostatic cysts), primary (prostatic cysts) or secondary (to other diseases particularly benign prostatic hyperplasia and squamous metaplasia).
The main problems with prostatic diseases are that 1/ they are often complex and different types of lesions can be observed simultaneously 2/ different etiological agents can occur independently or simultaneously 3/ a 'hemato-prostatic barrier' has been described which reduces treatment, penetration and efficacy 4/ they are often underestimated.
Indeed many clinical signs associated with prostate disease are non specific (hematuria, anuria, pain, constipation or locomotor disfunction) and are often first attributed to other organs (bladder or digestive diseases, or orthopaedic problems).
In all entire male animals of more than 4 to 5 years where one or several of the following clinical signs are observed, the prostate should be carefully investigated:
Hematuria is not necessarily associated with urination (blood is often observed passively in resting animals but also during urination), urinary incontinence with a full bladder, dysuria or anuria.
These are not constant but are sometimes the only clinical signs related to prostatic disease. They are caused by the hypertrophy of the prostate in the pelvis inducing constipation with sometimes characteristic flat faeces. These signs are highly variable in intensity and depend on the degree of the prostate enlargement and the position of the prostate. In general the enlarged prostate move cranially into the abdominal cavity and no digestive signs are observed. When inflammation is present (due to infectious processes or abscess), the digestive signs may be over expressed and pain may be one of the dominant features of the disease.
Stiffness, posterior lameness, paresis, oedema of the legs can be sometime observed in dogs with prostatic disease. These symptoms may appear suddenly (abscesses or acute prostatitis) or progressively (hyperplasia, tumours) and are related to local compression related to the enlargement of the prostate gland or to the presence of local metastasis.
General systemic signs of no specific origin
General signs such as fever, pain, prostration, anorexia, emesis, septicaemia may be associated with the condition. They sometimes can be the only symptoms detected by he owners, the more specific signs being more discrete. In all entire adult male dogs, presenting systemic clinical signs of no specific origins, a careful complete investigation of the prostate has to be realised.
Infectious prostatic diseases
Bacterial prostatitis is probably the second most common prostatic disorder in dogs after benign prostatic hyperplasia. The causes of canine prostatitis include E. Coli, Proteus spp., Pseudomonas spp., Brucella canis, Myco bacterium spp., Staphylococci, streptococci, and occasionally distemper virus and blastomyces dermatitidis. Microscopic examination of centrifugated prostatic fluid allows the observation of normal prostatic cells with numerous polymorphonuclear cells, red blood cells and sometime bacteria (figure 4)
Prostatitis can be acute and associated with many clinical signs or chronic and more discrete. During acute prostatitis, the hemato-prostatic barrier is no longer functional and antibiotic therapy has good chance of being effective. A broad-spectrum antibiotic should be used before obtaining an antibiogram. Chronic prostatitis is always more difficult to cure due to the functionality of the prostatic-prostatic barrier, reduced blood supply and organ fibrosis. The antibiotic choice has to be made taking into account the results of the antibiogram and the pH of the prostatic secretion. High dosages and long duration (minimum 4 to 6 weeks) treatments are the keys to treatment success. Since other conditions like BPH or metaplasia are often observed simultaneously castration, anti-androgen drugs, progestogens or 5-alpha reductase inhibitors can be used concurrently. When abscesses are present, antibiotics are used and omentalization with prostatic curettage may be necessary if cavities are more than 1 cm in diameter as detected by ultrasonography.
Endocrine prostatic conditions
Benign prostatic hyperplasia
Benign prostatic hyperplasia is observed in entire adult males or animals having been treated with androgenic hormones. The prostate is usually homogeneously enlarged. The exact aetiology of this condition in dog is not yet established but the condition is closely related to the effects of testosterone after transformation into dihydrotestosterone by the 5 alpha-reductase enzyme. Some effects of estrogens have also been proposed. Prostatic hyperplasia is considered to be normal in animal of more than 5 to 7 years of age but it is a only disease when clinical signs related to the hyperplasia are present. Prostatic hyperplasia may be present in some animals without any clinical significance but may be associated with mild to acute symptoms in others. The symptoms are as previously described. Castration is the most efficient treatment if the animal is not required for breeding. Progestogens, anti-androgens, 5-alpha reductase inhibitors or GnRH agonists or antagonists may be useful since they block the action of testosterone and of dihydrotestosterone. These have all been shown to be clinically efficacious.
Exogenous estrogens administered as therapeutic agents (this is no longer accepted) or endogenous estrogens from ea Sertoli cell tumours are for glandular epithelial pathology. The prostate is no longer homogenous in shape and often cysts or abscesses develop. Numerous squamous cells are observed in the prostatic fluid. Castration (in case of Sertoli cell tumours) or withdrawal of exogenous estrogens are curative.
Prostatic tumours (mainly adenocarcinomas) are fortunately rare in dogs. They may be observed in both young adults and old animals and are not directly androgen related in this species. Their appearance and size increase is rapid and in general metastasis are already present when a diagnosis is reached. Plurinecluated cells can sometimes be observed in the prostatic fluid. Adenocarcinoma tends to metastasise through the external and internal iliac lymph nodes to the vertebral bodies as well as to the lungs. The colonic and pelvic musculatures, the pelvis and urethra may also be invaded by direct extension of the tumours. The prognostic is poor and no treatment are up to now satisfactory. Anti-androgens, castration, partial prostatectomy or chemotherapy have been proposed but without major evidence of success.
Other prostatic conditions
These are often the consequence of prostatic gland obstruction related to calculi, cellular desquamation in metaplasia or hyperplasia. They are of no clinical significance as long as their size is small or infection does not occur. As for the abscesses, omentalization of the cavity is the best treatment and has nowadays replaced drainage or marsupialization.
Paraprostatic cysts are found laterally, outside the prostate and urinary bladder. Some may become confluent and contains large amount of fluid. The origin of the cysts remains unclear but suggests vestigial (mullerian ducts of the female) abnormalities. Surgical removal and omentalization are recommended.
Prostatic calculi and calcification are sometime observed but are of no clinical significance if no complications such as cysts, abscesses or infection are observed.
J. Verstegen, DVM, MSc, PhD and K. Onclin, DVM
Department of Small Animal Reproduction, Veterinary College, University of Liege