Editing Pyometra (section)

==Cause==
The risk of developing pyometra differs between dog breeds.<ref>{{cite journal|last1=Jitpean|first1=S|last2=Hagman|first2=R|last3=Ström Holst|first3=B|last4=Höglund|first4=OV|last5=Pettersson|first5=A|last6=Egenvall|first6=A|title=Breed Variations in the Incidence of Pyometra and Mammary Tumours in Swedish Dogs|journal=Reproduction in Domestic Animals|date=December 2012|volume=47|pages=347–350|doi=10.1111/rda.12103|pmid=23279535|doi-access=}}</ref> Pyometra is a result of hormonal and structural changes in the uterus lining.  This can happen at any age, regardless of how many heat cycles have occurred or previous pregnancies (or lack thereof), 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 has ended.<ref name=Ettinger>{{cite book|author1=Ettinger, Stephen J. |author2=Feldman, Edward C. |title=Textbook of Veterinary Internal Medicine|edition=4th|publisher=W.B. Saunders Company|year=1995|isbn=0-7216-6795-3}}</ref> Normally during this period, the [[cervix]], which opens during 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) &ndash;  known as cystic endometrial hyperplasia (CEH) &ndash; 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.<ref name=Romagnoli>{{cite journal | last = Romagnoli | first = Stefano | title = Canine Pyometra: Pathogenesis, Therapy and Clinical Cases | journal = Proceedings of the 27th World Congress of the World Small Animal Veterinary Association | year = 2002 | url = http://www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2002&PID=2686 | access-date = 2006-12-14 }}</ref>  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.<ref name=phl>{{cite web | last = Brooks | first = Wendy C. | title = Pyometra | work = The Pet Health Library | publisher = VeterinaryPartner.com | year = 2003 | url = http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=603 | access-date =2006-12-14 }}</ref>

===Hormonal influences and mis-mating shots===
Females that have received [[estradiol]] as a [[mismating shot]] in [[diestrus]] are at risk for more severe disease because [[estrogen]] increases the number of progesterone receptors in the endometrium. 25 percent of females receiving estradiol in diestrus develop pyometra.<ref name=Wingfield>{{cite book|author=Wingfield, Wayne E.|title=Veterinary Emergency Medicine Secrets|year=1997|publisher=Hanley & Belfus |editor=Hanley & Belfus, Inc.|isbn=1-56053-215-7}}</ref>  Pyometra is less common in female cats because progesterone is only released by the ovaries after mating.<ref name=Merck>{{cite web | title = Pyometra | work = The Merck Veterinary Manual | year = 2006 | url = http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/112009.htm | access-date = 2006-12-14 }}</ref> Also in cats, the risk of developing the disease differs depending on breed.<ref>{{cite journal|last1=Hagman|first1=R|last2=Ström Holst|first2=B|last3=Möller|first3=L|last4=Egenvall|first4=A|title=Incidence of pyometra in Swedish insured cats.|journal=Theriogenology|date=1 July 2014|volume=82|issue=1|pages=114–20|pmid=24726694|doi=10.1016/j.theriogenology.2014.03.007|doi-access=free}}</ref>