By Dr. Luke Peterson, DVM
I always have a small amount of extra sympathy for an intact male dog when he enters the exam room. A truly thorough physical exam of such a patient requires a digital rectal exam to evaluate the prostate gland. In truth, most male dogs we see are neutered and have very few prostate problems but occasionally we see (and feel) prostate disease in our patients. There are four common disease processes in the canine prostate; benign prostatic hyperplasia, prostatic infections resulting in prostatic abscesses and prostatitis, benign prostatic cysts, and prostate cancer. Each of these have many symptoms in common but it is important to identify and distinguish some differences so if your dog incurs one of the more serious of these diseases you may more rapidly get them the appropriate treatment needed. The biggest take away this article offers is the treatment options that may be able to preserve your male’s reproductive utility.
Benign prostatic hyperplasia (BPH) is the most common prostate disorder in dogs and is found in most intact males older than six years of age. However, as you may already be assuming, most of these never get enlargement to the degree that it causes any noticeable problems for the dog. It occurs due to hormonal stimulation from dihydrotestosterone. Dogs with clinical BPH often have histories of straining to defecate or producing ribbon-like stool and/or bloody urine and are otherwise healthy. Unlike men, dogs rarely have residual urine retention. A diagnosis is made by performing a rectal exam and x-rays and possibly ultrasound. The most successful and frequently recommended treatment is castration. Of course, if you have intentions of breeding, castration is less than desired. The only medical treatment that has had long-term success for managing BPH in breeding males is use of drugs like Finasteride (Proscar®) and Dutasteride (Avodart®) that were developed for treating men with BPH. Dogs undergoing treatment with these drugs have successfully sired litters. Finasteride is available as a generic so it is not terribly expensive to use. Personally, I have never managed a case with these drugs so cannot give anymore perspective on them.
Prostatic infections vary in their onset to severity but ultimately progress to life threatening illness if left untreated. The prostate is normally protected from bacterial infection by antibodies that are produced locally, prostatic antibacterial factor, and removal of bacteria by the process of urination. It is presumed that prostates with BPH are more prone to infections as there is an alteration in the normal antibacterial mechanisms. Bacteria most commonly associated with prostate infections are E. coli, Staphyloccocus, Streptococcus, and Mycoplasma. Dogs with acute onset prostatitis or prostate abscess have acute onset of severe illness including lethargy, abdominal pain, may have bloody preputial discharge or bloody urine. They are often dehydrated, off feed, have a fever, and may develop septicemia or endotoxemia from the toxins produced by the bacteria. Palpation of the prostate is extremely painful for these dogs. If I think a dog has a prostate infection, I have someone hold on to him really well before I do a rectal exam because as soon as a finger touches that prostate, that dog is going to turn around and bite. I have seen a lot of stoic hound dogs but have never had one that could tolerate the pain of prostatitis. The diagnosis is often confirmed with x-rays, abdominal ultrasound, and may also include bacterial culture of prostate fluid or abscess fluid. These dogs are often ill enough that blood testing is done to evaluate if other body systems are affected secondary to the bacterial infection. I have treated prostate infections in dogs that went from “normal” to toxic in a 24 hour period. I suspect these were dogs with prostatic abscesses that ruptured and had a large amount of bacterial toxins released into their circulatory system in a rapid time frame. Prostate abscesses should be on your list of possibilities if you have a male dog go downhill quickly. Treatment includes intravenous fluids to rehydrate and flush out the urinary tract, antibiotics, anti-inflammatories, and some strong pain medication. The best choice of antibiotics for these dogs is a drug class called the fluoroquinolones. The prostate gland has a unique anatomic barrier called the blood-prostate barrier which prevents most other classes of antibiotics from entering prostate tissue. The fluoroquinolones are the exception. Canine FDA veterinary approved fluoroquinolones include enrofloxacin (Baytril® and generics), orbifloxacin (Orbax®), and marbofloxacin (Zenequin®). The other benefit of this drug class is its broad spectrum to cover the most common bacteria associated with prostate infections. The downside is cost. These are also the most expensive of all the different classes of antibiotics. The minimum time to treat these dogs with antibiotics is two weeks with three being better. Prostate abscesses recur in about 10% of treated cases. Because pre-existing BPH has been associated with prostate infections, castration is also recommended for these dogs once they have finished the antibiotic treatment regimen to prevent future recurrences. Again though, if you would like to use the male for breeding be sure to discuss this with your veterinarian so they understand your desire to forgo castration.
Prostatic cysts are less serious than prostate infections. They occur for various reasons but are essentially a large fluid filled sac which causes enlargement of the prostate in the region of the cyst as opposed to BPH which causes symmetrically generalized enlargement of the entire prostate gland. These are often treated by drainage and surgical removal of the cyst. Again, castration is recommended but may be avoided in breeding stock.
Prostate cancer is by far the worst of the four prostate diseases in dogs. The average age of onset is 10 years old so most of these males will be past their reproductive careers. Interestingly, neutered dogs are at higher risk for prostate cancer than are intact males. The cancer invades the lymph nodes beneath the lumbar spine and also invades the pelvic bones and lumbar vertebral bone. The prostate gland becomes enlarged and makes it difficult for stool to pass through the colon. These dogs are often initially evaluated for the complaint of constipation. Other common symptoms include straining to urinate, weight loss, and decrease in appetite. A rectal exam reveals an irregular prostate and x-rays of the prostate region often confirms an abnormal gland along with enlarged lymph nodes and invasion of the cancer into the surrounding bony areas. Unfortunately, this diagnosis is basically a death sentence. Surgery, chemotherapy, hormone therapy, and radiation therapy have had virtually no success in improving the quality or length of survival for these dogs.