Peritonitis in the horse

In the preceding report, Semevolos et al. (2006) present a thorough discussion on a very rare cause of colic: small intestinal diverticuclosis. However, what makes these cases even more unusual is the rupture of diverticulae in 2 horses, causing peritonitis and evidence of systemic shock. Although the rarity of this condition deserves further comment, there is also some practical information that can be obtained from this report that is helpful to equine practitioners. Most importantly, the authors documented evidence of peritonitis of unknown origin (prior to surgery) that worsened over time, and was associated with important systemic findings of shock such as tachycardia. This in itself prompted surgical exploration, which I think was clearly indicated. Although colic was noted in one of the horses, it was not the principal clinical sign, and is not a requirement for the need for surgical exploration. In other words, practitioners should keep in mind that deteriorating systemic condition localized to the abdomen, particularly where there is evidence of progressive peritonitis, should prompt veterinarians to offer surgery. Even if the condition cannot be surgically corrected, as in these cases, a more accurate prognosis can be given to the owner, and abdominal lavage is far easier to accomplish via a midline incision under general anesthesia. Abdominal drains are also easier to place with the horse under general anesthesia. This simply involves placement of a large tube like a chest trocar adjacent to the abdominal wound, followed by a securing suture pattern. Overall, the notion that surgery is not indicated in certain cases of peritonitis should be dismissed. When following the progression of peritonitis, as was clearly demonstrated in the present report, it is important to make sure that the abdominocentesis technique itself does not contribute to abnormal laboratory findings. Previous studies have shown that repeated abdominocenteses using a needle lead to elevated protein and nucleated cell count levels in normal horses, presumably as a result of intestinal trauma (Juzwiak et al. 1991) Although the degree of abnormal abdominocentesis findings in this report overshadowed this problem, it is worthwhile considering which technique to use when there is a likelihood of repeat abdominocentesis. In these cases, use of sharp incision of the linea alba and placement of a teat cannula into the abdomen may be indicated as an alternative to placement of a needle. The authors have developed the interesting hypothesis that infiltration of eosinophils ultimately leads to muscular hypertrophy of the intestinal wall, followed by formation of diverticulae. This is probably correct, but it is worth considering the possibility that a diverticulum may form first, followed by partial intestinal obstruction and subsequent hypertrophy. For example, there is a previous report of a jejunal diverticulum in a horse that had not developed hypertrophy or rupture, despite the fact that it had signs of colic (Cook et al. 1996), suggesting that in some cases there may be alternate explanations. Nonetheless, finding eosinophils in the lamina propria and submucosa probably played a role in the pathophysiology of the cases in the present report. The reason for eosinophillic infiltration, such as chronic parasitism, is deserving of further study. Overall, these cases demonstrate a methodical and pragmatic approach to peritonitis in the horse. Multiple diagnostic modalities, including physical examination, clinical pathology, ultrasound and rectal palpation ultimately gave the veterinarians the information needed to make the best possible clinical decision for these horses.