Can Pagoda Red staining be used for histopathological differentiation of canine allergic dermatitis?

Allergic dermatopathies are pruritic cutaneous diseases often considered as diagnostic challenges due to the clinical similarity among its different types. On histopathological examination, a pattern of perivascular infiltrate composed of mononuclear cells and neutrophils can be identified in the four types of allergies. The marked presence of eosinophils suggests the division of the diseases into groups with small and large numbers of these cells, wich may be clearly evidenced through stains such as Pagoda Red. The objective of this work was to histologically characterize and quantify the eosinophils in skin of animals with allergic dermatitis. Histological slides from cutaneous biopsies of dogs with a suggestive clinical history of allergic dermatitis were selected and subdivided in two experimental groups according to the presence of eosinophils: group 1, animals with suspected canine atopic dermatitis or contact dermatitis (with little or none eosinophils), and group 2, animals suspected of ectoparasites allergy or food allergy. Pagoda Red staining was used in order to quantify eosinophils with a significant value of p≤0.05. The most prevalent epidermal changes in both groups were acanthosis and orthokeratosis. Perivascular infiltrate was composed of neutrophils, plasma cells, monocytes, lymphocytes and eosinophils. Regarding the quantification of eosinophils, there was a significant difference between the groups (p = 0.05). It was concluded that Pagoda Red staining allows quantification of eosinophils for differentiation of subtypes of allergic dermatitis in dogs, and may be used as an alternative easily accessible in the identification of eosinophils in canine allergic dermatitis.