CHAPTER 11 ATOPIC DISEASE 177
DIFFERENTIAL DIAGNOSIS
Cutaneous adverse reactions to food: may cause identical lesion distribution and
physical examination findings; often nonseasonal; may occur concurrently with AD;
differentiation made by response to restricted-ingredient diet.Flea bite hypersensitivity: may occur concurrently with AD; most often affects
the dorsal lumbosacral region; differentiation made by noting lesion distribution,
response to flea control.Sarcoptic mange: can develop at any age; causes severe pruritus of the ventral chest,
lateral elbows, lateral hocks, and pinnal margins; differentiation made by positive skin
scrapings and/or complete response to miticidal therapy.Demodicosis: not primarily pruritic; pruritus develops with secondary infec-
tion; differentiation made by positive skin scrapings and response to miticidal
therapy.Dermatophytosis: not primarily pruritic; differentiation made by positive fungal cul-
ture and/or response to antifungal therapy.
Pyoderma: common secondary to AD in dogs; usually caused byStaphylococcus
pseudintermedius; characterized by follicular papules, pustules, crusts, and epidermal
collarettes.Malasseziadermatitis: characterized by erythematous, scaly, crusting, greasy, licheni-
fied dermatitis; malodor; demonstration of numerous budding yeast organisms by
skin cytology, favorable response to antifungal therapy.Contact dermatitis (allergic or irritant): may cause severe erythema and pruritus of the
feet and thinly haired areas of the ventral abdomen; history of exposure to a known
contact sensitizer or irritant, response to a change of environment, and patch testing
may be diagnostic; uncommon in dogs and cats.DIAGNOSTICS
There is no definitive test for atopic disease: presumption of diagnosis is made only
after the exclusion of other causes of pruritus, appropriate symptom history, and clin-
ical examination.Determination of criteria to establish the diagnosis of canine AD is evolving; the fol-
lowing should be used to aid the identification of potential cases:
Age of onset<3 years
Mostly indoors
Corticosteroid-responsive pruritus
Chronic or recurrent yeast infections
Affected front feet
Affected ear pinnae
Nonaffected pinnal margins
Nonaffected dorsal lumbosacral region.