Page 1258 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Skin 1233

VetBooks.ir to deep perivascular dermatitis with eosinophilia head-shaking because it is a cost-effective, weight-
independent treatment option that is not banned
(also frequently observed with insect and food
hypersensitivity).
Intradermal skin testing is currently used to iden- by the drug testing show authorities, has mini-
mal to no long-term adverse effects and may ulti-
tify environmental allergens for inclusion in immu- mately lead to a cure. Reported success rates vary
notherapy treatment sets, including moulds, mites, between 60 and 80%.
dusts, insects, weeds, grasses and trees. The allergy Hypoallergenic shampoos and rinses, lime sul-
test is typically performed with sedation and reac- phur, antihistamines and tricyclic antidepres-
tions are read at 30 minutes and 4 hours post intra- sants (see Insect bite hypersensitivity, p. 1218),
dermal injection of dilute concentrations of test omega-6/omega-3 fatty acids, pentoxifylline and
allergens. As there is local amplification of IgE in topical and systemic glucocorticoids can be used.
response to percutaneous absorption of allergens, Prednisolone (1 mg/kg q12 h) is used until control
intradermal allergy testing still provides the most is established. Once stability is reached, the daily
accurate assessment of the local immune response dose is reduced to alternate-day low-dose morning
and results in fewer false-positive and false-negative therapy. Dexamethasone is another readily avail-
findings. Positive results should always be analysed in able oral glucocorticoid with excellent anti-inflam-
the light of historical data. It is important to ensure matory activity (administered at 0.05–0.1 mg/kg
that the patient is completely free of glucocorticoids, daily for 3–7 days, then tapered to 0.01–0.02 mg/
antihistamines and progestagens prior to testing. kg q48–72 h for maintenance). Recently, off-label
Several laboratories offer serum allergy test- use of oclacitinib, an oral medication that blocks
ing but the value of these tests is controversial. Janus–kinase receptors 1 and 3 and the effects of
Evaluation of serological tests revealed a sensitivity IL-31 (a pruritogenic cytokine), has anecdotally
of 47.3% and a specificity of 81.7%, with a positive helped to alleviate itch at doses between 0.1 and
predictive value of 68.7% and a negative predictive 0.25 mg/kg once to twice daily. Studies to evalu-
value of 64.7%, in horses with atopic disease and ate side effects and long-term adverse reactions
horses without atopic disease, respectively. When are pending.
comparing different serological allergy testing com- Given that allergies are a common presenting
panies, there are often discrepancies between and complaint in equine medicine, and long-term con-
sometimes within laboratory findings. For instance, trol of symptoms using anti-inflammatory medi-
not all laboratories account for cross-reactive carbo- cation carries side effects, costs and drug testing
hydrate determinants, which have been shown to be liabilities, intradermal allergy testing and devel-
a major cause of false-positive reactions in serologi- opment of ASIT should be a serious consideration
cal allergy testing. There is also a lack of correlation for any horse experiencing allergies for greater
between intradermal allergy testing and serological than 4–6 months of the year.
allergy testing.
Prognosis
Management The prognosis is guarded. Results will be dependent
Treatment of equine allergies requires a multi- on the multiplicity of causes and the possibility of
modal approach including environmental control, reduction of these causes. It is important to remem-
topical and systemic therapy, and allergen- specific ber that the horse may have more than one condi-
immunotherapy (ASIT). ASIT should be con- tion concurrently, therefore treatment of only one
sidered for all proposed presentations of equine of the causal agents may not resolve the pruritus or
allergies including hives, heaves, scratches and the urticaria.