Small Animal Dermatology, 3rd edition

636 DISEASES/DISORDERS

DIFFERENTIAL DIAGNOSIS

 Cutaneous adverse reaction to food

 Atopic dermatitis

 Malasseziadermatitis

 Flea-allergic dermatitis

 Dermatophytosis

 Pyoderma

 Demodicosis

 Contact allergy

 Pelodera dermatitis

 Pruritic impetigo

 Otitis externa/media

 Pediculosis

 Seborrhea

DIAGNOSTICS

 ELISA technique: identifySarcoptesmite-infested dogs; detection of circulating IgG

antibodies againstSarcoptesantigens; seroconversion 2–5 weeks after exposure; high

false-positive results in dogs previously treated for scabies mites and false-negative

results in young dogs and those receiving corticosteroids; not widely used.

 Positive pinnal-pedal reflex: rubbing the ear margin between the thumb and forefinger

induces scratching with the ipsilateral hindleg; occurs in 75–90% of cases of scabies,

notoedres, and otodectes; not diagnostic.

 Superficial skin scrapings:
Technique (also see Chapter 5):

Apply a small amount of mineral oil directly onto the selected lesional skin

Scrape the area in the direction of hair growth and transfer accumulated

material to the glass slide

Select several sites for sampling and sample a large surface area; preferred

sites include pinnal margins and lateral forelegs just proximal to the elbow

Finding mite eggs or feces is diagnostic of infestation

Sarcoptes scabiei:may be difficult to demonstrate; positive in less than 50% of

scrapings

Notoedres cati:large number of mites easily demonstrated in scrapings.

 Touch tape prep and “flea combing” for collection of epidermal debris:Cheyletiella

spp. (Figure 42.16).

 Ear swab in mineral oil:Otodectes cynotis.

 Fecal flotation: occasionally reveals mites or ova.

 Diagnosis inferred by favorable response to a “therapeutic trial” for suspect cases with

negative skin scrapings.

 Dogs with nonseasonal pruritus that respond poorly to steroids should be treated with

a scabicide (even if skin scrape results are negative) to definitively rule out sarcoptic

mange.