472


EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2018) 30 (9) 472-474 doi: 10.1111/eve.12723


Clinical Commentary Eosinophilic intestinal diseases of the horse


J. Schumacher* and R. Legere Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA. *Corresponding author email: schumjo@auburn.edu


Keywords: horse; eosinophil; intestine


Summary Eosinophilic intestinal diseases of the horse are not commonly reported. Similar diseases are reported in man, but for either species, these eosinophilic diseases, are poorly understood. Eosinophilic intestinal disease may be accompanied by eosinophilic disease of other organs, or eosinophilia may be restricted to the intestine. When infiltration of eosinophils is restricted to the intestine, horses have a good prognosis for resolution of clinical signs, even though the treatment may include celiotomy with intestinal decompression or resection and administration of a corticosteroid. When eosinophilic intestinal disease is accompanied by infiltration of other organs, such as skin, pancreas, lungs or liver, the horse’s prognosis for survival is very poor.


Infiltration of the equine intestine with eosinophils is known to be caused by endoparasitism (French et al. 1996; Love et al. 1999; Headley et al. 2008; Dıez de Castro et al. 2016), or, rarely, Pythium insidiosum (Allison and Gillis 1990; Morton et al. 1991; Purcell et al. 1994), but infiltration of eosinophils into the equine intestine is also frequently an idiopathic condition. An understanding of intestinal disease of the horse characterised by idiopathic infiltration of eosinophils is somewhat hampered by nomenclature. Saying that a horse has eosinophilic enteritis seems akin to saying a horse is brown; not much information is conveyed by that description. Until the aetiologies of eosinophilic intestinal diseases are determined, we believe that the terms eosinophilic colitis, eosinophilic enteritis and eosinophilic enterocolitis, which may have different meanings to different clinicians, should not be used. Instead, we believe that terminology used in recent reports of eosinophilic intestinal disease in the horse, as shown in Fig 1, should be used when describing idiopathic, eosinophilic intestinal disease. Classification of equine idiopathic eosinophilic intestinal


diseases is currently based primarily on the clinicopathological characteristics displayed by the affected horse. A major grouping of these diseases distinguishes systemic eosinophilic disease (i.e. multisystemic eosinophilic epitheliotropic disease or MEED) from idiopathic eosinophilic diseases confined to the intestine (EDCI). The clinical presentation and the course of disease of horses with EDCI differ from that of horses with MEED. In addition to having eosinophilic infiltration of intestine (usually large colon), horses with MEED have eosinophilic infiltration of the liver, pancreas, oesophagus, skin, blood and oral cavity (Lindberg et al. 1985; Nimmo Wilkie et al. 1985; Gibson and Alders 1987; La Perle et al. 1998). Horses with MEED are often presented for weight loss, lethargy, subcutaneous oedema and skin disease, and, rarely, respiratory disease, whereas horses with eosinophilic infiltrates confined to the intestinal tract are usually presented


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for signs of abdominal pain (Scott et al. 1999; Edwards et al. 2000; Southwood et al. 2000; Swain et al. 2003; Archer et al. 2006; Perez Olmos et al. 2006; Makinen et al. 2008; De Bont et al. 2013, 2018; Archer et al. 2014). Horses with MEED almost never survive, whereas the prognosis for survival for horses with EDCI tends to be favourable, even though the treatment may include celiotomy with intestinal decompression or resection and administration of a corticosteroid. A salient feature of horses with MEED is protein-losing


enteropathy, whereas horses with EDCI are unlikely to have substantial changes in the serum concentration of protein. Eosinophilic disease of horses confined to the intestine has been further categorised into diffuse eosinophilic enteritis (DEE) and idiopathic focal (or multifocal) eosinophilic enteritis (IFEE). Horses are diagnosed with IFEE during celiotomy, performed because of signs of abdominal pain, when circumferential mural bands or plaque-like constrictions are found in the small or large intestine. These grossly visible lesions are considered by some to be pathognomic for IFEE (Scott et al. 1999). Of the intestinal diseases characterised by infiltration of


eosinophils, DEE is the most poorly described. Gross intestinal lesions of horses with DEE were not described in a report that proposed characterising DEE as an eosinophil-dominated, idiopathic, inflammatory condition affecting intestinal segments, not associated with systemic infiltration of eosinophils (Makinen et al. 2008). Clinical signs displayed in horses with DEE were similar to those displayed by horses with IFEE, and thickened intestine was found during ultrasonographic examination of the abdominal viscera, palpation of intestine per rectum, or celiotomy (Archer and Southwood Parente 2014). Some horses with DEE may have signs similar to those with MEED. Four horses with diarrhoea and weight-loss reported by Pass and Bolton (1982) were assumed by other researchers to have DEE (Archer et al. 2006), but Pass and Bolton (1982) believed the four horses to have MEED when comparing case details with Nimmo Wilkie et al. (1985), who reported clinical details of five horses with MEED. Whether horses with DEE sometimes develop diarrhoea is not clear from a review of the literature, but like horses with MEED, horses with DEE may experience weight loss and develop a low concentration of plasma protein (Archer and Southwood Parente 2014). An intense focal inflammatory infiltration of eosinophils


involving the submucosa and disrupting the architecture of the muscularis externa was seen during histological examination of the grossly visible focal lesions in intestinal tissue harvested from horses with IFEE (Makinen et al. 2008). Results of that study showed that IFEE is a focally exacerbated inflammatory reaction in horses with DEE, indicating that IFEE and DEE may be manifestations of the same disease. Edwards


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