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Pyometra and Cystic Endometrial Hyperplasia (Uterine Infection) in Dogs

Occurrence: common
Location of illness: Abdomen/pelvis

Author: Dr. med. vet. Gisa Löwe | Last modified: 06.11.2025

Pyometra and cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. are conditions of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. in dogs characterized by the accumulation of pus and thickening of the uterine lining. These conditions usually occur in older, intact female dogs and can be life-threatening if not treated promptly.

The most important facts at a glance

Pyometra and cystic endometrial hyperplasia (CEH) are diseases that commonly occur in dogs after hormonal changes in the reproductive cycle. CEH is caused by repeated cycles without pregnancy, which leads to thickening of the uterine lining and cystA cyst is a closed sac that may contain fluid, air, or other material. Cysts can occur in any part of the body and vary in size and cause. formation, which promotes bacterial growth. Pyometra often develops after estrusEstrus, also known as heat, is the phase in the reproductive cycle of female mammals when they are receptive to mating. In dogs and cats, this is the time when they are ready to mate., when progesterone weakens the uterus’s immune defenses, making it easier for bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease. such as Escherichia coli to enter. Typical symptoms include vaginalVaginal refers to anything related to the vagina, the muscular tube that connects the external genitalia in female mammals to the uterus. discharge, loss of appetite, increased thirst and urination, vomiting, weakness, and fever. Clinical symptoms, blood tests, and imaging techniques are used for diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients., with ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. examinations being particularly helpful. The main treatment is surgical removal of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. and ovaries, as this method eliminates the risk of recurrence. Antibiotics are also an important part of the treatment. The prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. is good with timely diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and treatment, although complications such as kidney failureRenal failure is a condition in which the kidneys can no longer adequately perform their function of filtering and excreting waste products from the blood. It can be acute or chronic and requires immediate medical treatment. and sepsisSepsis is a life-threatening condition caused by the body's overwhelming response to an infection, which can lead to damage to its own tissues and organ failure. can occur. Spaying is recommended for preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring., while close monitoring is important for breeding female dogs. Research focuses on genetic, hormonal, and environmental factors, as well as the development of less invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. treatment methods and better diagnostic tests.

Causes

The uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. of the female dog consists of various layers, of which the mucous membrane (endometrium) plays an important role in preparing for a possible pregnancy. During the reproductive cycle, the endometrium undergoes changes controlled by hormones such as estrogenEstrogen is a group of steroid hormones that are primarily responsible in female animals for regulating the reproductive system and developing female characteristics. In dogs and cats, estrogens play an important role in the estrous cycle. and progesterone.

Cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. (CEH) is caused by repeated cycles of hormonal changes without pregnancy. This leads to a thickening of the uterine lining and the formation of cysts. These changes create a favorable environment for the growth of bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease., which can eventually lead to pyometra.

Pyometra usually develops a few weeks after estrusEstrus, also known as heat, is the phase in the reproductive cycle of female mammals when they are receptive to mating. In dogs and cats, this is the time when they are ready to mate., when the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. is under the influence of progesterone. This promotes the secretion of mucus and reduces the immune defenses, making it easier for bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease. to enter and multiply. The most common pathogens associated with pyometra are bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease. such as Escherichia coli.

Symptoms

Very common symptoms:

Common symptoms:

The symptoms of pyometra are varied and depend on the severity of the disease. The most common symptoms include increased thirst (polydipsiaPolydipsia refers to an increased feeling of thirst and increased fluid intake. It can be a symptom of various diseases, including diabetes mellitus and kidney disease.) and increased urination (polyuriaPolyuria refers to a significantly increased urine output. It can be a symptom of various diseases, including diabetes mellitus, kidney disease, and hormonal disorders.). These symptoms occur because the bacterial infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. releases toxins that impair kidney function.

Other signs include lethargy, loss of appetite, and vomiting. Female dogs with open pyometra, in which the cervixThe cervix is the lower part of the uterus that opens into the vagina. It plays an important role in reproduction and menstruation. is open, may have a foul-smelling, purulentPurulent refers to pus or the production of pus, which may indicate a bacterial infection. Purulent inflammatory conditions are often painful and may have significant swelling and redness. discharge from the vagina. In closed pyometra, this discharge is absent, which can make diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. more difficult.

Fever is another possible symptom, although it does not occur in all affected dogs. In severe cases, a state of shock can occur, which is life-threatening and requires immediate treatment.

Diagnosis

The diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. of pyometra is based on a combination of clinical symptoms, blood tests, and imaging procedures. A complete blood count may show elevated white blood cells, indicating an infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease.. Kidney values may also be elevated, indicating impaired kidney function due to the toxins.

UltrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. examinations are a valuable tool to identify an enlarged, fluid-filled uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane.. X-rays can also be useful to assess the size and shape of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane., but provide less detailed information than ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow..

In some cases, a biopsyA biopsy is a medical procedure in which a small amount of tissue is removed from the body to be examined under a microscope for signs of disease. Biopsies can help diagnose cancer and other conditions. of the uterine lining may be necessary to confirm the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and rule out other conditions. An accurate diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. is crucial for choosing the right treatment method.

Therapy

Treatment for pyometra usually requires surgical removal of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. and ovaries, a procedure known as ovariohysterectomyAn ovariohysterectomy is a surgical procedure in which the ovaries and uterus are removed. It is a standard procedure for castration / neutering female animals, especially dogs and cats. An ovariohysterectomy not only prevents unwanted reproduction, but also prevents certain diseases of the female reproductive organs.. This surgery is the preferred method because it eliminates both the infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. and the risk of recurrence.

In some cases, especially in young breeding female dogs, medical treatment may be considered. This involves the administration of prostaglandins to open the cervixThe cervix is the lower part of the uterus that opens into the vagina. It plays an important role in reproduction and menstruation. and promote uterine contraction to expel the pus. However, this method is associated with risks and is less reliable than the surgical option.

Antibiotics are an essential part of the treatment, regardless of the method chosen. They help fight the infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. and support recovery. The selectionSelection refers to the process of natural or artificial selection of specific individuals for reproduction, based on desired genetic traits. In breeding, this is applied to promote specific characteristics in dogs and cats. of antibiotics is ideally based on a culture and sensitivity tests of the bacteriaBacteria are microscopic, single-celled organisms that exist in almost every environment on Earth. Some types of bacteria are beneficial or even essential to life, while others can cause disease..

Prognosis and follow-up care

The prognosis for female dogs with pyometra depends on the severity of the disease and the speed of treatment. With timely diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and surgical intervention, the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. is usually good, and most dogs recover completely.

Complications can occur, especially if the pyometra is advanced or the female dog is already in a weakened condition. These include kidney failureRenal failure is a condition in which the kidneys can no longer adequately perform their function of filtering and excreting waste products from the blood. It can be acute or chronic and requires immediate medical treatment., sepsisSepsis is a life-threatening condition caused by the body's overwhelming response to an infection, which can lead to damage to its own tissues and organ failure., and shock, which can significantly impair the chances of survival.

Long-term complications are rare, but in some cases, fertilityFertility refers to the ability to conceive and bear offspring. In women, it refers to the ability to initiate and carry a pregnancy; in men, it refers to the ability to produce fertile sperm. problems can occur, especially if medical treatment has been attempted. However, a full recovery and return to normal activity is to be expected in most operated dogs.

Prevention

The most effective method for preventing pyometra is spaying, in which the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. and ovaries are surgically removed. This not only prevents pyometra but also reduces the risk of other hormone-dependent diseases and certain cancers.

For breeding female dogs in which spaying is not immediately considered, close monitoring during and after estrusEstrus, also known as heat, is the phase in the reproductive cycle of female mammals when they are receptive to mating. In dogs and cats, this is the time when they are ready to mate. is important to recognize early signs of pyometra. Regular veterinary examinations can help monitor the health of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. and identify potential problems early.

A balanced diet and good general care also help to strengthen the female dog’s immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. and reduce the risk of infections. Avoiding unnecessary hormonal treatments can also reduce the risk of cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. and subsequent pyometra.

Outlook on current research

In current research on pyometra and cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. in dogs, scientists are focusing on the genetic, hormonal, and environmental factors that contribute to the development of these diseases. There is evidence that genetic predispositions may play a role, as some dog breeds are more commonly affected than others. Older, unspayed female dogs, especially of breeds such as the Bernese Mountain Dog, Golden Retriever, or Collie, are particularly susceptible. Researchers are investigating the genetic markers associated with an increased risk of developing these diseases to develop better preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. strategies.

Another focus of research is on the role of hormones, especially progesterone, which thickens the lining of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane., thus contributing to the development of cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease.. Studies are examining how hormonal changes during the sexual cycleThe sexual cycle refers to the reproductive cycle in female animals, which consists of several phases, including estrus (heat), during which the animal is receptive to mating. The cycle varies in duration and specific phases depending on the animal species. of dogs can lead to an increased susceptibility to infections and inflammatory conditions. The research aims to understand the exact mechanism by which progesterone and other hormones affect uterine health and how these processes can be modulated by therapeutic interventions.

In the field of treatment methods, alternative approaches to conventional ovariohysterectomyAn ovariohysterectomy is a surgical procedure in which the ovaries and uterus are removed. It is a standard procedure for castration / neutering female animals, especially dogs and cats. An ovariohysterectomy not only prevents unwanted reproduction, but also prevents certain diseases of the female reproductive organs. (spaying), which is currently the most effective treatment for pyometra, are being investigated. Scientists are experimenting with drug treatments that combine hormonal blockers or antibiotics to treat milder cases and reduce the need for surgery. However, these studies are still in the early stages, and it is still unclear to what extent such treatments can be a viable alternative to surgery.

Another promising area of research is the development of diagnostic tests that allow early detection of cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. and pyometra. Advances in imaging technology, such as high-resolution ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. or MRI, as well as the analysis of biomarkers in the blood, could facilitate diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. in the future and improve the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop.. Such tests could allow veterinarians to detect the disease at an earlier stage, before serious symptoms occur, thus improving the treatment outcome.

In summary, research on pyometra and cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. in dogs aims to better understand the underlying causes of these diseases, develop more effective and less invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. treatment methods, and improve diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients.. There is still much to be done, but advances in these areas could lead to better management and a higher quality of life for affected animals in the long term.

Frequently asked questions (FAQs)

What is Pyometra? Pyometra is a serious and potentially life-threatening condition in dogs in which pus accumulates in the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane.. It often occurs in older, unspayed female dogs, typically a few weeks after a heat cycle. It is a hormonally mediated disease that is often caused by an infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease..
What symptoms does a female dog with pyometra have? The most common symptoms include vaginalVaginal refers to anything related to the vagina, the muscular tube that connects the external genitalia in female mammals to the uterus. discharge, increased drinking and urination, lethargy, loss of appetite, and vomiting. In severe cases, there may be fever, abdominalThe term "abdominal" refers to anything that concerns the belly or the abdomen. It is an adjectival expression used to describe the location, symptoms, or conditions that occur in the abdominal area. pain, and a bloated abdomenThe abdomen, also known as the abdominal cavity, is the part of the body located between the rib cage and the pelvis. It houses several important organs, including the stomach, liver, kidneys, intestines, and spleen.. If the uterus is closed, the symptoms may be more severe because the pus cannot drain.
What is cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease.? Cystic endometrial hyperplasiaHyperplasia refers to an increase in the number of cells in a tissue or organ, leading to enlargement. This can be a normal reaction or a sign of a disease. is a precursor to pyometra and describes a thickening of the uterine lining due to cystic changes. This thickening is caused by hormonal changes, especially by progesterone, and can make the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. more susceptible to infections that can result in pyometra.
How is pyometra diagnosed? DiagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. is usually made through a combination of clinical examination, blood tests, and imaging procedures such as ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. or X-rayX-ray is an imaging technique that uses X-rays to create images of the inside of the body. It is often used to diagnose bone fractures, lung diseases, and other conditions.. These tests help assess the condition of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. and rule out other possible causes of the symptoms.
How is pyometra treated? The most effective treatment for pyometra is surgical removal of the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. and ovaries, called ovariohysterectomyAn ovariohysterectomy is a surgical procedure in which the ovaries and uterus are removed. It is a standard procedure for castration / neutering female animals, especially dogs and cats. An ovariohysterectomy not only prevents unwanted reproduction, but also prevents certain diseases of the female reproductive organs.. In mild cases, especially if the uterusThe uterus, also known as the womb, is a female reproductive organ in which the fetus grows and develops during pregnancy. It consists of muscle tissue and is lined with a mucous membrane. is open, medical treatment with antibiotics and hormonal blockers can be attempted, but this is often less effective and carries the risk of relapse.
Can pyometra be prevented? The most reliable method to prevent pyometra is spaying (ovariohysterectomyAn ovariohysterectomy is a surgical procedure in which the ovaries and uterus are removed. It is a standard procedure for castration / neutering female animals, especially dogs and cats. An ovariohysterectomy not only prevents unwanted reproduction, but also prevents certain diseases of the female reproductive organs.) before the first heat cycle. Since the disease is strongly hormonally influenced, removing the ovaries significantly reduces the risk. Regular veterinary examinations can also help detect early signs.
Is pyometra only a problem in older dogs? While pyometra is more common in older dogs, younger, unspayed female dogs can also be affected. The female dog’s cycle plays a role, and any female dog that goes into heat carries a potential risk, especially as she gets older.
What risk factors increase the likelihood of pyometra? Risk factors include age, breed, hormonal status, and whether the female dog has ever whelped. Certain breeds are at higher risk, as are female dogs that are repeatedly suppressed from going into heat or have received hormones for contraception.
What are the chances of survival with pyometra? With prompt and appropriate treatment, especially through surgery, the chances of survival are good. Untreated, however, the disease can quickly become life-threatening. The earlier the treatment, the better the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop..
Are there long-term consequences after treatment for pyometra? After a successful ovariohysterectomyAn ovariohysterectomy is a surgical procedure in which the ovaries and uterus are removed. It is a standard procedure for castration / neutering female animals, especially dogs and cats. An ovariohysterectomy not only prevents unwanted reproduction, but also prevents certain diseases of the female reproductive organs., most female dogs recover completely without long-term health problems. In cases where surgery is not performed, recurrentRecurrent refers to a disease that repeatedly returns or worsens after a temporary remission or improvement. infections and complications can occur, requiring ongoing monitoring.