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
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?
Dogs that are seen early in the disease may have
a slight vaginal discharge and show no other
signs of illness. However, most dogs with
pyometra are not seen until later in the
illness. 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"). Dogs diagnosed in
the early stage of the disease are very good
surgical candidates. The surgery is only
slightly more complicated than a routine spay.
However, most dogs are diagnosed when they 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 1-2 weeks.
My dog is a valuable breeding bitch. Can
anything else be done other than surgery?
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 treatment:
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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