A dog presents with pruritus and erythematous papules. Which three differential diagnoses and one diagnostic test per differential best fit this presentation?

• A. Atopic dermatitis (skin scrapings/cytology), flea allergy dermatitis (flea comb or flea counts), food allergy (elimination diet trial)
• B. Contact dermatitis (patch testing), mange (skin scrape), seborrhea (cytology)
• C. Dermatophytosis (culture), mites (skin scrape), seborrheic keratosis (biopsy)
• D. Lichen planus (biopsy), autoimmune pemphigus (serology), granulomatous disease (imaging)

Answer: (A)

When a dog presents with pruritus and erythematous papules, the most fitting trio of possibilities is allergic or allergic-like skin disease. The strongest combination is atopic dermatitis, flea allergy dermatitis, and food allergy dermatitis, each paired with a practical test that helps support the diagnosis.

For atopic dermatitis, skin scrapings and cytology are used to check for secondary infections or parasites that can worsen itch and mimic other conditions, helping to interpret the ongoing allergic itch in the context of chronic disease. For flea allergy dermatitis, a thorough flea search with a flea comb or flea counts is key, because fleas or flea dirt may be present even if fleas aren’t visibly jumping on the animal at the visit. For food allergy dermatitis, an elimination diet trial is the go-to test; observing improvement during 8–12 weeks on a restricted diet, followed by re-challenge, helps prove or disprove dietary ownership of the pruritus. Other options involve conditions and tests that are less directly aligned with this common pruritic presentation.