What is pyometra?
In its simplest terms, pyometra is an infection in the uterus. However, most
cases of pyometra are much more difficult to manage than a routine infection.
Infection in the lining of the uterus is established as a result of hormonal
changes. Following estrus ("heat"), progesterone levels remain elevated for
8-10 weeks and thicken the lining of the uterus in preparation for pregnancy.
If pregnancy does not occur for several estrus cycles, the lining continues
to increase in thickness until cysts form within it. The thickened, cystic lining
secretes fluids that create an ideal environment in which bacteria can grow.
Additionally, high progesterone levels inhibit the ability of the muscles in
the wall of the uterus to contract.
Are there other situations that cause the changes in the uterus?
Yes. The use of progesterone-based drugs can do this. In addition, estrogen
will increase the effects of progesterone on the uterus. Drugs containing both
hormones are used to treat certain conditions of the reproductive system.
How do bacteria get into the uterus?
The cervix is the gateway to the uterus. It remains tightly closed except
during estrus When it is open, bacteria that are normally found in the vagina
can enter the uterus rather easily. If the uterus is normal, the environment
is adverse to bacterial survival; however, when the uterine wall is thickened
and cystic, perfect conditions exist for bacterial growth. In addition, when
these abnormal conditions exist, the muscles of the uterus cannot contract properly.
This means that bacteria that enter the uterus cannot be expelled.
When does it occur?
Pyometra may occur in young to middle-aged dogs; however, it is most common
in older dogs. After many years of estrus cycles without pregnancy, the uterine
wall undergoes the changes that promote this disease.
The typical time for pyometra to occur is about 1-2 months following estrus
What are the clinical signs of a dog with pyometra?
The clinical signs depend on whether or not the cervix is open. If it is open,
pus will drain from the uterus through the vagina to the outside. It is often
noted on the skin or hair under the tail or on bedding and furniture where the
dog has laid. Fever, lethargy, anorexia, and depression may or may not be present.
If the cervix is closed, pus that forms is not able to drain to the outside.
It collects in the uterus causing distention of the abdomen. The bacteria release
toxins which are absorbed into the circulation. These dogs often become severely
ill very rapidly. They are anorectic, very listless, and very depressed. Vomiting
or diarrhea may be present. Toxins from the bacteria affect the kidney's ability
to retain fluid. Increased urine production occurs, and the dog drinks an excess
of water. This occurs in both open- and closed-cervix pyometra.
How is it diagnosed?
A very ill female dog that is drinking an increased amount of water and has
not been spayed is always suspected of having pyometra. This is especially true
if there is a vaginal discharge or an enlarged abdomen. Dogs with pyometra have
a marked elevation of the white blood cell count and often have an elevation
of globulins (a type of protein produced by the immune system) in the blood.
The specific gravity of the urine is very low due to the toxic effects of the
bacteria on the kidneys. However, all of these abnormalities may be present
in any dog with a major bacterial infection.
If the cervix is closed, radiographs (x-rays) of the abdomen will often identify
the enlarged uterus. If the cervix is open, there will often be such minimal
uterine enlargement that the radiograph will not be conclusive. An ultrasound
examination can also be helpful in identifying an enlarged uterus and differentiating
that from a normal pregnancy.
How is it treated?
The preferred treatment is to surgically remove the uterus and ovaries. This
is called an ovariohysterectomy ("spay"). However, these dogs are quite ill
so the surgery is not as routine as the same surgery in a healthy dog. Intravenous
fluids are often needed before and after surgery. Antibiotics are given for
My dog is a valuable breeding bitch. Can anything else be done other than
There is a medical approach to treating pyometra. Prostaglandins are a group
of hormones that reduce the blood level of progesterone, relax and open the
cervix, and contract the uterus to expel bacteria and pus. They can be used
successfully to treat this disease, but they are not always successful and they
have some important limitations.
1. They cause side-effects of restlessness, panting, vomiting, defecation,
salivation, and abdominal pain. The side-effects occur within about 15 minutes
of an injection and last for a few hours. They become progressively milder with
each successive treatment and may be lessened by walking the dog for about 30
minutes following an injection.
2. There is no clinical improvement for about 48 hours so dogs that are severely
ill are poor candidates.
3. Because they contract the uterus, it is possible for the uterus to rupture
and spill infection into the abdominal cavity. This is most likely to happen
when the cervix is closed.
There are some important statistics that you should know about this form of
1. The success rate for treating open-cervix pyometra is 75-90%.
2. The success rate for treating closed-cervix pyometra is 25-40%.
3. The rate of recurrence of the disease is 50-75%.
4. The chances of subsequent successful breeding is 50-75%.
What happens if neither of the above treatments are given?
The chance of successful treatment without surgery or prostaglandin treatment
is extremely low. If treatment is not performed quickly, the toxic effects from
the bacteria will be fatal. If the cervix is closed, it is also possible for
the uterus to rupture, spilling the infection into the abdominal cavity. This
will also be fatal.
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