Page 590 - Small Animal Clinical Nutrition 5th Edition

612 Small Animal Clinical Nutrition

(GALT) is likely to be very limited if the antigen is fed to a
patient with a highly porous mucosal barrier. Irritable bowel
VetBooks.ir Box 31-1. Gastroscopic Food Sensitivity syndrome is a disease of dogs characterized by chronic recurrent
Testing.
abdominal pain and large bowel diarrhea (Guilford, 1996a).
Gastroscopic food sensitivity testing (GFST) is a diagnostic tech- Feeding changes will often alleviate the signs of irritable bowel
nique in which food extracts (5,000 to 15,000 protein nitrogen disease, implying that food sensitivity plays a role in this syn-
units/ml) are dripped onto the gastric mucosa by means of the drome. In the experience of one of the authors (WGG), avoid-
operating channel of an endoscope. The site is then observed for ing gas-producing foods (e.g., homemade vegetable-based
two to three minutes. Mucosal swelling suggests an immediate foods) or foods with a high fat content is particularly advanta-
sensitivity to the food extract tested. Erythema, blanching, edema geous in the management of dogs with irritable bowel syn-
and petechiation at the mucosal site also suggest the test subject drome. In affected dogs, the adverse reactions to these nutrients
is hypersensitive to the food, and the food, therefore, should not
be used as part of the sensitive patient’s diet. Sampling of the are most likely due to food intolerance rather than food allergy.
mucosal site with subsequent measuring of histamine levels,
other mediator levels or mast cell degranulation can be used to Diagnostic Methods
determine whether the response was immune mediated. The The diagnosis of an adverse reaction to a food is confirmed by
diagnostic accuracy of GFST isn’t known. elimination-challenge trials (Jackson, 2009). In food-sensitive
patients, resolution of clinical signs occurs after elimination of
The Bibliography for Box 31-1 can be found at the responsible food from the diet followed by a return of the
www.markmorris.org. signs when the patient is challenged with the original food.
Subsequently, feeding the elimination food should again allevi-
ate clinical signs. Correct design of elimination-challenge trials
is imperative for reliable diagnosis and is described below in the
their dermatoses (Scott et al, 2001; Paterson, 1995; Loeffler et Feeding Plan section.
al, 2004, 2006).The increased frequency of defecation will nor- Failure to challenge a suspected food-sensitive patient will
malize with use of an appropriate elimination food (Loeffler et lead to marked over diagnosis of food sensitivity (Guilford et al,
al, 2004). 2001). However, whether to challenge the patient or not is a
There are at least five subacute to chronic GI conditions decision that needs to be made collectively with the owner.
thought to involve food allergy in people: 1) food protein- Many owners are happy with a presumptive diagnosis of food
induced enterocolitis, 2) food-induced colitis syndrome, 3) sensitivity and do not wish to undertake a challenge test. After
food-induced malabsorption syndrome, 4) gluten-sensitive a diagnosis of food sensitivity is made, further cycles of elimi-
enteropathy and 5) allergic eosinophilic gastroenteritis (Samp- nation-challenge trials may then be undertaken in an attempt
son, 1991; Sampson et al, 2001; Motala, 2008). All of these to identify the responsible food ingredients. It is noteworthy
conditions can occur in dogs and cats. The role of food allergy that dietary trials confirm or rule out adverse reactions to food
in canine and feline IBD is unknown. Hypersensitivity to food but do not indicate the underlying mechanism (allergy or intol-
is probably involved in the pathogenesis of this syndrome; at erance).
least some affected animals could be more appropriately diag- The place of skin tests, laboratory assays and endoscopic
nosed as suffering from food protein-induced enterocolitis. provocation tests remains uncertain in the diagnosis of food
Dogs with GI diseases, including IBD, have more food aller- sensitivity. None of these are suitable as screening tests for
gen-specific serum IgG than normal dogs, a finding that may adverse reactions to food because they do not screen for the
reflect increased antigen exposure due to increased mucosal entire spectrum of adverse reactions to foods (both allergy and
permeability (Foster, 2003). Currently, 10% of dogs with IBD intolerance). Some tests (e.g., measurement of food-specific
diagnosed by one of the authors (WGG) have positive gastro- serum IgE) suggest that an adverse reaction to a particular food
scopic food sensitivity tests (GFST) to food antigens (Box 31- (identified in an elimination-challenge trial) may be due to a
1). Positive GFST results to foods used in the treatment of the type-1 hypersensitivity response rather than another type of
disease are often detected during followup endoscopic studies. allergic reaction or a food intolerance. However, at the present
This finding strongly implies that food allergy is involved in the time, intradermal testing, radioallergosorbent tests (RASTs)
perpetuation of IBD but that it may not be the primary cause. and enzyme-linked immunosorbent assays (ELISAs) for food
That is, inflammation of the mucosa predisposes animals to the hypersensitivity are considered unreliable in patients with der-
development of acquired food allergies. Therefore, a change in matologic (Jeffers et al, 1991; Kunkle and Horner, 1992) and
food antigens may temporarily reduce the immune-mediated GI disease (Foster, 2003). Although it is sensible to avoid feed-
mucosal inflammatory response. The longevity of this amelio- ing proteins that have caused positive gastroscopic or colono-
ration is questionable; however, because most of the so-called scopic food sensitivity tests (especially more severe reactions
“hypoallergenic” foods commonly used in veterinary medicine such as edema and petechiation), the diagnostic accuracy of
contain intact proteins that are hypoallergenic primarily by these endoscopic provocation tests requires further evaluation
virtue of their novelty to the host’s immune system. The dura- (Guilford et al, 1994; Vaden et al, 2000; Allenspach et al, 2006)
tion of protein novelty to the gut-associated lymphoid tissue as does the diagnostic accuracy of ultrasonography for food sen-