Pyometra in a pluriparous Standardbred mare.
Keywords: pyometra, equine, treatment.
| Primary author: Dr Rob Lofstedt. Dept of Health Management, Atlantic Veterinary College. Additional authors: Dr Anna Potter (primary clinician & corresponding author: apotter@upei.ca ) and Dr Martha Mellish, both of the section of Theriogenology, Dept of Health Management, Atlantic Veterinary College & Dr Shannon Martinson of the Department of Pathology and Microbiology, Atlantic Veterinary College. Editors: Drs Rob Lofstedt (lofstedt@upei.ca) and Allan Gunn (algunn@csu.edu.au). |
Early in April 2019, an enlarged, fluid-filled uterus was palpable. On transrectal ultrasonography, this fluid was partially echogenic and suspected to be pus (see figure 1). Due to its size and dependency, it was not possible to delineate the uterus. It was also not possible to palpate the ovaries. Trans-abdominal ultrasonography revealed that the uterus was highly distended and at its cranial aspect, lay adjacent to the xiphoid process. Nevertheless (and typical for mares with pyometra) the mare was bright, alert and responsive and had a normal hemogram.
The mare’s ovaries containing no luteal tissue; not an unusual finding in equine pyometra. Pyometra in mares does not necessarily develop in a progesterone dominated milieu i.e. unlike the situation in cattle, cervical closure and myometrial quiescence due to progesterone is not required for the development of pyometra. In mares it is more likely that retention of pus within the uterus is a function of deficient myometrial activity than cervical pathology (See LeBlanc et al 1994 and Troedsson 1999), especially in older animals. Occasionally however, cervical pathology is implicated.
Figure 1. Note the accumulation of moderately echogenic pus within the uterine lumen and follicles within the ovaries. This image also serves as an excellent example of two common ultrasonographic artifacts; reverberation and enhancement through transmission (ETT). Image Copyright: Dr Martha Mellish. mmellish@upei.ca Image size: 862 x 947 px.
During per-vagina examination, the mare’s cervix was found to be closed tightly. Cervical patency was only established after approximately 20 minutes of digital manipulation and only then, did pus drip from the vulva lips as shown in figure 2. This suggested that cervical pathology was indeed implicated in retention of pus within the uterus, perhaps in conjunction with poor myometrial tone as discussed earlier. As seen in figure 2, a large diameter stomach tube was eventually passed through the cervix to drain the uterus. Cytology and culture were performed prior to drainage of the pus.
Figure 2. The main image shows how pus dripped from the mare’s vulva after gradual dilation of the cervical canal. The inset shows how pus was then drained from the uterus. Image Copyright: Dr Martha Mellish. mmellish@upei.ca Image size: 1513 x 1024 px
Several days after initial drainage, the uterus was flushed repeatedly with saline (see figure 3). Then oxytocin was administered to facilitate the expulsion of any remaining fluid. In addition, 1000 mg of prostaglandin E-1 (misoprostol) in methylcellulose was applied to the cervix and cervical canal to facilitate dilation for drainage and further treatment.
Figure 3. Serial saline flushes showing the increase in clarity with each successive flush. Copyright: Dr Anna Potter apotter@upei.ca Image size 2000 x 1215
Pending culture and sensitivity results, the uterus was lavaged daily with lactated ringers or saline solution. Two days after the initial drainage, culture results revealed Pseudomonas aeruginosa, sensitive to gentamicin, amikacin and enrofloxacin. Treatment was initiated with 1g of gentamicin buffered with 10ml of 8.4% sodium bicarbonate infused into the uterus after uterine lavage, every 24 hours for five days. On the fourth day of antibiotic treatment, an additional treatment of 100ml of 90% DMSO was added into the second to last flush for three days. These treatments were followed by twice daily oxytocin treatment at appropriate intervals.
Two weeks after initial dilation of the cervix and uterine flushing, ultrasonography revealed a uterus devoid of any free fluid, multiple small follicles in both ovaries and a corpus luteum. Uterine culture at that time revealed Citrobacter koseri and Streptococcus zooepidemicus. However, approximately a month days later, the uterus had re-filled with pus and uterine culture again revealed growth of Streptococcus zooepidemicus. Six days later i.e. approximately 48 days from the initial dilation of the cervix, approximately 2.5 liters of pus was drained and treatment with saline flushes, DMSO and oxytocin treatment were re-started. On this occasion, treatment lasted for four days; the antibiotic being penicillin, not gentamicin. On day four, another uterine culture revealed growth of Citrobacter koseri.
The mare was re-examined about three and a half months after initial presentation and summer rest on pasture. At that time, three liters of pus was drained from her uterus, followed by saline lavage.
In early November, 2019, re-examination revealed that a large amount of pus had accumulated in the uterus again. The mare was then euthanized and submitted for post mortem exam. Her pus-filled uterus is shown in the inset of Figure 4.
Figure 4. The pus-filled uterus of the mare seen during postmortem examination. The appearance of pus shown here is typical for equine pyometra. Image Copyright: Dr Shannon Martinson. smartinson@upei.ca Image size: 1500 x 911 px.
Figure 5. It is probable that the cervical lesion seen here was implicated in the development of pyometra, together with general cervical cicatrization and myometrial compromise. The cause of the lesion was unknown and could not have been caused by foaling as this was a nulliparous mare. Image Copyright: Dr Shannon Martinson. smartinson@upei.ca Image size: 2002 x 1232 px.
Bearing in mind the difficulty of cervical dilation in this case and the absence of spontaneous drainage of pus before and after treatment, cervical pathology (seen in figure 5; probably fibrosis after cervical damage) was probably important in the development of pyometra in this case.
Editor’s comments: In light of the typical recurrence and usually dismal prognosis of equine pyometra, some may be critical of the handling of this case with regard to repeated attempts at physical drainage, antibiotic and anti inflammatory treatment. Consider however, that in recent years, the use of cervical wedge resection and intra-cervical stents have provided favorable outcomes in cases of equine pyometra. This suggests that even if one presumes the presence of myometrial inadequacy, attempts to dilate the cervix both physically and hormonally (using PGE analogs) may hold merit and should be considered in some cases. Of course, wedge resection and cervical stents should be considered as well.
The bacteriology in this case also deserves comment. The significance of any of the bacteria isolated is open to question. For example, a literature search of Citrobacter koseri is devoid of examples of infertility in mares so this can be presumed to be a contaminant. Also, Streptococcus zooepidemicus is not only a common cause of endometritis in mares, it is a common commensal and contaminant of uterine cultures as well. Also, Pseudomonas aeroginosa is commonly isolated from soil samples and it therefore likely to be present on mares at pasture. The absence or presence of bacteria in single or serial cultures in this mare is also open to discussion; bacterial cultures vary in success according to sampling or culture methods. Essentially therefore, the bacterium or bacteria responsible for pyometra in this case remains a question.
Selected references:
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