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===Clinical Signs===
===Clinical Signs===
Signs are often, but not always, seasonal. Pruritus is the hallmark of atopic dermatitis and may be the only complaint. This gives rise to self-trauma, causing lesions. Lesions commonly include alopecia, erythema, scaling, crusting, excoriations and salivary staining. Macular-papular eruptions are occasionally seen<sup>2</sup>. With time, lichenification, and hyperpigmentation develops. Because the route of allergen contact is thought to be percutaneous absorption<sup>1, 2</sup>, it follows that hairless regions are most frequently affected: the face, ears, axillae, feet and inguinal regions are predilection sites. Secondary infections such as superficial staphylococcal pyoderma and [[Malassezia pachydermidis|''Malassezia'']] are common, and otitis externa often occurs concurrently<sup>2, 3, 4</sup>. A small number of cases exhibit only chronic or recurrent otitis externa. Another uncommon presentation is allergic rhinitis, manifesting as sneezing, nasal discharge or allergic conjunctivitis<sup>1, 2</sup>.
Signs are often, but not always, seasonal. Pruritus is the hallmark of atopic dermatitis and may be the only complaint. This gives rise to self-trauma, causing lesions. Lesions commonly include alopecia, erythema, scaling, crusting, excoriations and salivary staining. Macular-papular eruptions are occasionally seen<sup>2</sup>. With time, lichenification, and hyperpigmentation develops. Because the route of allergen contact is thought to be percutaneous absorption<sup>1, 2</sup>, it follows that hairless regions are most frequently affected: the face, ears, axillae, feet and inguinal regions are predilection sites. Secondary infections such as superficial staphylococcal pyoderma and [[Malassezia pachydermidis|''Malassezia'']] are common, and otitis externa often occurs concurrently<sup>2, 3, 4</sup>. A small number of cases exhibit only chronic or recurrent otitis externa. Another uncommon presentation is allergic rhinitis, manifesting as sneezing, nasal discharge or allergic conjunctivitis<sup>1, 2</sup>.
Signs commonly seen in different species are:
:Dogs - face rubbing and foot licking; secondary [[Pyoderma|pyoderma]] or [[Skin Other - Pathology#Secondary seborrhea|seborrhea]]
:Cats - facial, ear or generalised pruritus, [[Feline Miliary Dermatitis|miliary dermatitis]], [[Feline Eosinophilic Granuloma|eosinophilic granuloma complex]], symmetric [[Alopecia|alopecia]]
:Horses - pruritic hea, pinnae, ventrum, legs, tailhead or recurrent [[Urticaria|urticaria]]
===Laboratory Tests===
===Laboratory Tests===
===Pathology===
===Pathology===
Gross findings reflect the lesions seen in life.
Gross findings reflect the lesions seen in life and lesions are generally due to self-trauma.
Histological changes are non-specific but include acanthosis, a mixed mononuclear perivascular dermatitis, sebaceous gland metaplasia and secondary superficial pyoderma<sup>1</sup>.
Histological changes are non-specific but include acanthosis, a mixed mononuclear perivascular dermatitis, sebaceous gland metaplasia and secondary superficial pyoderma<sup>1</sup>.
Other microscopical findings include: hyperplastic superficial perivascular dermatitis, mast cells, eosinophils and nonmetachromatic mononuclear cells. Perivascular inflammation may be involved especially in horses.
==Treatment==
==Treatment==
[[Category:Allergic Skin Diseases]]
[[Category:Allergic Skin Diseases]]
[[Category:Dermatological Diseases - Dog]][[Category:Immunological Diseases - Dog]] [[Category:Dermatological Diseases - Cat]][[Category:Immunological Diseases - Cat]]
[[Category:Dermatological Diseases - Dog]][[Category:Immunological Diseases - Dog]] [[Category:Dermatological Diseases - Cat]][[Category:Immunological Diseases - Cat]]
[[Category:Expert Review]]
[[Category:Type I Hypersensitivity Diseases]]
[[Category:Integumentary System - Hypersensitivity Reactions]]