Pyometra - Cause of Pyometra

Cause of Pyometra

Pyometra is a result of hormonal and structural changes in the uterus lining. This can happen at any age, whether she has bred or not, and whether it is her 1st or 10th heat (although it becomes more common as the dog gets older). The main risk period for a female is for eight weeks after her peak standing heat (or estrous cycle) has ended. Normally during this period, the cervix, which was open during her heat, begins to close, and the inner lining begins to adapt back to normal. However, cystic hyperplasia of the endometrium (inner lining of the uterus) – known as cystic endometrial hyperplasia (CEH) – may occur at this time for some animals, as an inappropriate response to progesterone.

Under these circumstances, bacteria (especially E. coli) that have migrated from the vagina into the uterus find the environment favorable to growth, especially since progesterone also causes mucus secretion, closes the cervix (preventing uterine drainage), and decreases uterine contractility. The condition of the cervix is a major factor in the severity of the condition.

• If the cervix is open, the infected material can leave the body, and this is far easier and safer to treat. This is known as open pyometra.
• If the cervix is fully closed, there is no discharge from the vulva, and like in appendicitis, the uterus may rupture and pus escapes into the abdomen, causing peritonitis and possible rapid death. This is known as closed pyometra.