PYOMETRA: THE END OF MOTHERHOOD?

© Mushing Magazine – Featured in the Nov/Dec issue 2005 Issue:In the past we believed that pyometra was simply a bacterial infection of the uterus. Now we know that although infection is present in most cases, this common condition is caused by a hormonal abnormality. Pyometra occurs mainly in middle-aged and older intact females, but it can occur in younger dogs as well. It is life threatening if not promptly treated. Symptoms of the disease occur within two to four months after a heat cycle during which fertilization did not occur, the period called diestrus. The most common symptoms of pyometra that prompt the owner to take a bitch to the veterinary clinic are depression, anorexia (lack of appetite), scanty or profuse vaginal discharge, vomiting, diarrhea, polydipsia (excessive thirst) or polyuria (excessive urine flow). The vaginal discharge is usually yellow-gray or brown, and has a fetid odor. Among symptoms less commonly observed by the owner are a distended abdomen and enlargement of the vulva. The rectal temperature is usually normal or slightly elevated; however, in a severely toxic animal the temperature may be subnormal. Survival depends on quick recognition of these symptoms by the owner/breeder, who needs to seek medical attention immediately. Of the two main hormones produced by the ovaries, estrogen and progesterone, the large amounts of progesterone that are released during diestrus, or a heightened sensitivity of the uterus to this hormone, represent the cause of pyometra. This leads to the formation of cysts containing numerous secretory cells in the endometrium, the inner lining of the uterus. These secretory cells release a large volume of fluids into the interior (lumen) of the uterus. Bacteria, which have had an opportunity to enter the uterus from the vagina during proestrus, namely, the 8 to 10 weeks before onset of estrus, when the cervix is dilated, are believed to play a role as well. Estrus is the time when the bitch is receptive to the male. In addition, inflammatory cells invade the uterine wall, leading to varying degrees of inflammation. The excess fluid, along with a thickening of the walls of the uterus, leads to a tremendous enlargement of the organ. The uterus consists of a body and two horns. In a healthy dog, the horns of the uterus are smaller than a pencil. However, in a dog with pyometra they can swell to the size of a cucumber, translating to a marked weight increase of the uterus. In a 40-lb dog, the increase may be from a weight of 2 to 4 ounces to a weight of 1 to 4 pounds. Initially, fluid flows out through the vagina, but eventually the cervix closes, trapping all of the fluid and pus within the uterus. Meanwhile, fluids and white blood cells in the uterus increase, followed by an even greater dilation of the organ. This continued swelling can lead to uterine rupture, spilling the fluid into the abdominal cavity. This, in turn, will quickly lead to peritonitis, an inflammatory condition of the inner lining of the abdominal cavity and outer lining of abdominal organs. If this occurs, the animal will expire in less than 48 hours. If rupture of the uterus does not occur, wastes and excess fluids are carried by the bloodstream to the kidneys, thus severely overloading them. Since the kidneys are unable to eliminate all of the wastes fast enough, they accumulate, leading to uremic poisoning. If not treated promptly, the dog will die of kidney failure.The diagnosis of pyometra is established based on history, physical examination, microscopic examination of vaginal swabs and several other tests, including a complete blood count, or CBC. Bitches with pyometra have variable CBC results. Those with a closed cervix often have marked increases in white blood cells, whereas those with less severe disease or an open cervix may have a normal white blood count. Many patients experience mild anemia due to leakage of red blood cells into the uterine fluids, or a decreased lifespan of the red cells. All CBC abnormalities usually resolve quickly after completion of treatment. The liver enzyme alkaline phosphatase and kidney function parameters are also evaluated in the diagnostic workup. A urinalysis is included. Many dogs with pyometra have concurrent urinary tract infections.Other tests include abdominal x-rays, which may reveal an enlarged uterus, and ultrasound. The latter is particularly important in differentiating pyometra from pregnancy, since ultrasound can demonstrate fetuses as early as 21 days after the beginning of diestrus. An enlarged uterus with a thickened wall, containing dense fluid, points to pyometra. Although most cases of pyometra can be diagnosed based on history, physical examination, radiographic and ultrasonographic findings, exploratory surgery provides the definitive diagnosis of the condition. The first choice of treatment, especially in severe cases, is the removal of the uterus and ovaries (spaying). If, however, the reproductive potential of the bitch is important to the owner, medical therapy with a prostaglandin may be considered. This could be risky, since approximately 48 hours will pass before improvement is manifested. Furthermore, there is a high relapse rate in prostaglandin-treated patients. According to Charles E. Carmichael, DVM, Diplomate ACVIM (Internal Medicine), of the Woodstock Veterinary Clinic, a large northern Illinois veterinary practice, “The success rate of prostaglandin treatment is 50 to 60 percent. This involves a hospital stay of 5 days, plus 2 to 3 weeks of antibiotic therapy. The dog will have to be carefully monitored for a recurrence of symptoms, with regular hospital checkups and blood tests. This could get the animal through another heat cycle, at which time breeding could be attempted. However, since there is a high recurrence rate of pyometra, I recommend spaying after the puppies are weaned.” Prostaglandins work by causing the uterus to contract and expel the fluid. If the uterus has not yet closed, and fluid is still draining, the chances of success of prostaglandin therapy are good. This mode of therapy should not be used if the cervix is closed, because of the risk of uterine rupture, or leakage of pus through the uterine tubes into the abdomen. Prostaglandin therapy is recommended only in dogs six years old or younger, who are in stable condition. Prostaglandin therapy is administered by means of intramuscular injections for 5 to 7 days. It can have adverse effects, such as panting, restlessness, vomiting, fever, abdominal pain and rapid heart rate. Other drugs (estrogens, androgens, ergot alkaloids, quinine and oxytocin) have been used in the past, but the results have not been successful. Antibiotic therapy as a single agent has been unsuccessful as well. Antibiotics are useful only as adjunct to prostaglandins. If prostaglandin therapy fails, or if the patient becomes very ill during therapy, spaying may be inevitable. Most pyometra cases are considered surgical emergencies, to be operated on as soon as the patient is stable enough to undergo general anesthesia. After the uterus is removed, pus should be aspirated from the organ and cultured, in order to determine what pathogens are present. This will aid in the choice of antibiotic to be administered after surgery. Despite aggressive therapy, the literature reports a postoperative mortality rate of 5 percent. Most patients recover uneventfully.Pyometra is a common and serious condition, which is best prevented by spaying at or before the age of six months. In the case of a brood bitch, it is advisable to have her spayed after her last litter. There are many other benefits of spaying, i.e., prevention of accidental breedings. Spaying reduces the chances of uterine and ovarian tumors. If performed before her first heat, spaying can significantly reduce a female’s chance of developing mammary cancer. Generally, spaying promises a longer, healthier life.Karen Gadke, PhD (Health Science) is a clinical study specialist, medical writer, author and lecturer. She has been mushing/racing since 1979. She owns both Siberians and Alaskans.

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