Page 458 - Cote clinical veterinary advisor dogs and cats 4th

204.e2 Contact Dermatitis

Contact Dermatitis
VetBooks.ir

• A generalized distribution may be present
BASIC INFORMATION
with contact reactions to shampoos. • A fungal culture should be considered,
especially in cats, to detect dermatophytosis.
Definition • The ears may be the only area affected if the • An elimination food trial may be performed
Cutaneous inflammation that occurs after offending substance is a topical otic medication. to rule out cutaneous adverse food reactions.
contact with an irritant or antigenic substance • The primary lesion is an erythematous • Intradermal skin testing may be performed
papular and macular eruption. to investigate atopic dermatitis.
Synonyms • Vesicles are occasionally present.
Allergic contact dermatitis, contact hypersen- • With chronic exposure, alopecia, lichenifica- Advanced or Confirmatory Testing
sitivity, irritant contact dermatitis tion, and hyperpigmentation develop. • Histopathologic evaluation may provide
supportive evidence and help differentiate
Epidemiology Etiology and Pathophysiology between allergic and irritant contact derma-
SPECIES, AGE, SEX • Allergic contact dermatitis is a type IV titis if biopsies are taken early in the disease
• Uncommon in dogs and rare in cats hypersensitivity disorder. The development of process. Results from biopsies of chronically
• Allergic contact dermatitis typically occurs clinical disease requires two stages: induction diseased skin are usually nonspecific.
in animals older than 1 year; irritant contact and elicitation. • Patch testing is a specific test for investigat-
dermatitis may occur at any age. ○ The induction phase is the time from ing allergic contact dermatitis. A series of
allergen exposure until the time lympho- compounds is applied to the skin for 48
GENETICS, BREED PREDISPOSITION cytes become programmed to recognize hours, and the degree of erythema, indura-
Short-coated breeds may be at increased risk. the allergen (lasts months to years; no tion, and papular eruptions caused by each
evidence of clinical disease). agent is evaluated. Standardized kits for
RISK FACTORS ○ Elicitation is the time from re-exposure veterinary medicine are not available, but
Concurrent inflammatory dermatoses, alopecia to the allergen to the development of human standardized kits have been used
cutaneous inflammation. This phase may successfully in dogs.
ASSOCIATED DISORDERS take several days. • Restriction and provocative exposure is
• Atopic dermatitis ○ Reported causes include shampoos, the most reliable test. Ideally, the animal
• Secondary bacterial or Malassezia dermatitis insecticides, topical/otic medications, should be bathed to remove all possible
plastic, detergents, wool, synthetic rugs, allergens and removed completely from the
Clinical Presentation fertilizers, cement, perfumed cat litter, and home environment for 2 to 4 weeks. After
DISEASE FORMS/SUBTYPES several species of plants. resolution, the animal is reintroduced to the
• Allergic contact dermatitis • Irritant contact dermatitis is an antigen- environment. A return of clinical signs will
• Irritant contact dermatitis independent process that is the result of typically occur in 24 to 72 hours in cases of
direct keratinocyte damage by the offending contact dermatitis.
HISTORY, CHIEF COMPLAINT compound. No induction phase is necessary.
• Allergic contact dermatitis Acids, alkalis, surfactants, solvents, enzymes, TREATMENT
○ The chief complaint is typically chronic and oxidants may cause irritant contact
pruritus that may be seasonal or nonsea- dermatitis. Treatment Overview
sonal, depending on the allergen. • Ideally, identify and remove offending
○ A recent change in environment or DIAGNOSIS substance.
housing is typically not noted because • If unable to identify and remove offending
signs may take months to years to develop Diagnostic Overview substance, nonspecific palliative therapy may
from the time of initial exposure. Contact dermatitis is difficult to definitively be necessary.
○ The animal is typically the only one in diagnose with commonly available clinical tools.
the household affected. Its diagnosis often relies on ruling out other Acute General Treatment
• Irritant contact dermatitis potential causes of inflammation in conjunction • Treat any secondary microbial infections.
○ The chief complaint may be acute cutane- with a suggestive history. More common causes • Identify and remove the offending substance.
ous pain rather than pruritus. of the apparent clinical signs need to be ruled • Palliative therapy with glucocorticoids
○ Onset of the condition often correlates out first. (prednisone 0.5-1 mg/kg PO q 24h initially,
with the introduction of a new substance. before weaning down based on response),
○ There may be more than one individual Differential Diagnosis pentoxifylline 15-20 mg/kg PO q 8-12h
affected (including the owner). • Parasitic: fleas, contagious acarioses (Sarcoptes, or topical tacrolimus 0.1% ointment may
Cheyletiella, Otodectes, Notoedres), Demodex, provide relief in cases of allergic contact
PHYSICAL EXAM FINDINGS Pelodera, chiggers, and hookworm dermatitis dermatitis.
Lesion distribution reflects the area of the body • Allergic: flea-bite hypersensitivity, atopic • Bathing the patient can help to speed resolu-
in contact with the offending substance. dermatitis, food hypersensitivity tion of irritant contact dermatitis.
• Sparsely haired areas and those areas in • Bacterial pyoderma
contact with the environment are more • Fungal: dermatophytosis, Malassezia Chronic Treatment
frequently affected (ventral surfaces of the dermatitis Long-term palliative therapy may be neces-
feet, chest, and abdomen, perineum, and • Cutaneous autoimmune diseases sary if clinical signs persist and the offending
scrotum). substance cannot be identified and removed.
• Regional dermatitis of the muzzle and chin Initial Database The treatment plan for each patient should be
may occur with reactions to substances such • Skin scrapings and cytologic examination chosen based on efficacy in that patient as well
as rubber chew toys or plastic food dishes should be performed to detect microbial or as long-term safety. For example, pentoxifylline
(rare). parasitic infections. is typically well tolerated and should be chosen

www.ExpertConsult.com