714 DISEASES/DISORDERS
DIFFERENTIAL DIAGNOSIS
Crusting diseases: if crust formation precedes other symptoms – drug eruption, pem-
phigus foliaceus, systemic lupus erythematosus additional causes for exfoliative der-
matitis.Allergic disorders: if pruritus is the initial clinical sign – flea-allergic der-
matitis, cutaneous adverse reaction to food, atopic dermatitis,Malassezia over-
growth/hypersensitivity.Parasitic diseases: canine and/or feline scabies, demodicosis, cheyletiellosis.
Infectious diseases: superficial and deep bacterial and fungal infections, leishmaniasis.
Keratinization disorders: nasodigital hyperkeratosis, zinc-responsive dermatoses.
Neoplasia: mast cell tumors and epitheliotropic lymphoma.
Metabolic disorders: hepatocutaneous syndrome (superficial necrolytic dermatitis).
DIAGNOSTICS
CBC/Biochemistry/Urinalysis
Often normal; abnormalities present may reflect severity of other systemic disease
processes.
Cytology/Serology/Virus Isolation
Rule out other differentials with skin scrapings and trichograms, dermatophyte cul-
ture, epidermal cytology.
Viral serology: FeLV and FIV; hemagglutination inhibition, virus neutralizing, com-
plement fixation, Western blot (immunoblot), or ELISA; demonstrate rising titers
indicative of active infection on paired serum samples.Virus isolation from crusted material is often diagnostic (90% positive in poxvirus
infection).
Polymerase chain reaction (PCR) or reverse transcriptase PCR (RT-PCR).
Cerebrospinal spinal fluid analysis, bone marrow aspirate.
Histopathologic Findings
Light microscopy:
Hyperplasia
Ballooning degeneration
Hydropic interface dermatitis
Syncytial-type giant cell formation within the epidermis and/or outer root sheath
of the hair follicle
Keratinocyte inclusion bodies