266 DISEASES/DISORDERS
Corticosteroids minimally helpful.
Lesions resolve 1–2 days after removal of irritant.
ACD
Rare in young animals; most animals chronically exposed to the antigen; extremely
rare in cats (e.g., exposure to d-limonene-containing insecticides).
Reported increased risk of ACD: Boston terrier, pit bull, boxer, dachshund,
weimaraner, German shepherd dog, poodle, wire-haired fox terrier, Scottish terrier,
West Highland white terrier, Labrador and golden retriever.Requires weeks to months of exposure for hypersensitivity to develop.
Reexposure results in development of clinical signs 3–5 days following exposure;
signs may persist for several weeks.
May respond to corticosteroids applied topically at the lesion or systemically; pruritus
returns after discontinuation if the antigenic stimulus persists.
Hyposensitization: no reported efficacy.
Prognosis: good if the allergen is identified and removed; poor if the allergen is not
identified, which may then require lifelong treatment.
CLINICAL FEATURES
Location determined by antigen contact; commonly limited to glabrous skin and
regions frequently in contact with the environment (chin, lip margins, ventral
neck, sternum, ventral abdomen, inguinum, perineum, scrotum, and ventral contact
regions of the tail and interdigital areas) (Figures 16.1–16.3).Reactions to topical medications (e.g., otic preparations or spot-on insecticides) usu-
ally localized (Figures 16.4, 16.5).
Thick hair coat of dogs can be an effective barrier against irritant and sensitizing
contactants; extreme erythroderma often stops abruptly at the hairline (Figure 16.6).
Initial erythema and swelling, leading to papules and plaques; vesicles uncommon.
Chronic exposure leads to lichenification and hyperpigmentation (Figure 16.7).
Generalized reactions, resulting from shampoos or insecticide sprays, less common.
Pruritus: moderate to severe.
Seasonal incidence may indicate a plant or outdoor antigen.
Reported offending substances: plants, mulch, cedar chips, fabrics, rugs, carpets, plas-
tics, rubber, leather, nickel, cobalt, concrete, soaps, detergents, floor waxes, carpet
and litter deodorizers, herbicides, fertilizers, insecticides (including newer topical
flea treatments), flea collars, topical preparations (especially neomycin).DIFFERENTIAL DIAGNOSIS
Atopy
Food allergy