Page 219 - Cote clinical veterinary advisor dogs and cats 4th

92 Atopic Dermatitis

PHYSICAL EXAM FINDINGS Staphylococcus spp and Malassezia spp fre- • Poor correlation between intradermal and
Dogs: quently cause severe disease exacerbation serologic testing; none of them is standard-
VetBooks.ir rubbing, scooting, head shaking), initially • The role of food allergens as possible triggers information for avoidance and allergen-
ized. It is probable that the most appropriate
through secondary infection.
• Pruritus (scratching, licking, chewing,
for atopic dermatitis is currently accepted.
specific immunotherapy (ASIT) would be
with mild or no visible lesions
• Possible primary erythema (macules or small
on every patient, but this may not always
papules) DIAGNOSIS gathered by performing both types of testing
• Areas most commonly affected include be practical.
muzzle, periocular region, ears, flexor aspect Diagnostic Overview • Mite infestations (Sarcoptes, Notoedres,
of elbows, carpal and tarsal joints, interdigital The diagnosis of atopic dermatitis is based on Otodectes, Cheyletiella) cause cross-reactions
spaces, axillary and inguinal areas, ventrum, history, physical examination, and ruling out with house dust and storage mite antigens,
and perianal area. other causes of a similar presentation. Although often resulting in false-positive reactions in
• Different phenotypes exist (e.g., dorsum a different set of clinical criteria have been intradermal and blood testing. These infesta-
commonly affected in Chinese Shar-peis and proposed in dogs to help support a diagnosis tions should be treated and allergy testing
Labrador retrievers; urticaria is common in of atopic dermatitis (the latest one being the postponed for 3-4 months if possible.
boxers). Favrot criteria), there is common agreement • Annual vaccinations can cause increased
• Secondary skin lesions: excoriations, alopecia, that the diagnosis should not be based exclu- levels of allergen-specific IgE for up to 3
hyperpigmentation, lichenification, crusting sively on any set of criteria. weeks.
• Saliva staining of hair may be noted. • In geographic areas with well-defined,
• Secondary bacterial and yeast infections of Differential Diagnosis pronounced pollen and mold seasons, allergy
skin and ears, and acute moist dermatitis • Ectoparasites: Sarcoptes, Demodex (especially testing is best performed at season’s end or
(hot spots) may also be noted (pp. 247 and D. gatoi and D. injai), Cheyletiella, Notoedres, within 2 months after the peak allergy
851). Otodectes, Trombicula, fleas, lice season.
Cats: • Bacterial infections: especially Staphylococcus • Drug therapy can suppress allergy test results.
• Pruritus (including excessive grooming) pseudintermedius ○ Withdraw oral, topical, and long-acting
rapidly leading to excoriation, especially face, • Fungal infections: Malassezia, dermatophy- injectable glucocorticoids for 2-3, 2, and
pinnae, and neck tosis 4-8 weeks, respectively. This applies to
• Papulocrustous (miliary) dermatitis: especially • Other hypersensitivities: fleas, food, contact, intradermal and serologic testing.
dorsum drug ○ Withdraw antihistamines and omega-6/
• Eosinophilic granuloma complex lesions: • Behavioral disorders: feline psychogenic omega-3 fatty acid–containing supple-
indolent ulcer (upper lip), eosinophilic alopecia (rare) ments and diets at least 7 days before
plaque (mainly ventral abdomen), eosino- • Neoplasia: epitheliotropic lymphoma intradermal testing.
philic granuloma (p. 300). ○ Cyclosporine does not appear to affect
• Self-induced alopecia: more or less sym- Initial Database allergy test results. However, withdrawal
metrical (especially abdomen, medial thighs, • The minimum database for a pruritic patient for days to weeks might be considered if
front limbs, rump) should include a complete history and administered for a number of months.
physical examination and a thorough der- ○ Oclacitinib and lokivetmab (Apoquel and
Etiology and Pathophysiology matologic examination for ectoparasites, Cytopoint) do not appear to interfere with
• Atopic dermatitis is a genetically pro- bacteria, and yeast. results of intradermal or serologic testing.
grammed, multifactorial, allergic skin disease • An initial dermatologic database (p. 1091) ○ Avoid acepromazine, oxymorphone, and
in which the patient becomes sensitized to ○ Skin scrapings morphine if sedating the patient for
environmental allergens. ○ Trichography intradermal testing.
• Atopic animals are thought to have a defec- ○ Skin and ear cytologic examination
tive epidermal barrier function (aggravated ○ +/− Fungal culture in cats TREATMENT
by numerous factors such as the diet,
microbial exposure, stress, climate, exposure Advanced or Confirmatory Testing Treatment Overview
to skin irritant) and polarization toward a Testing for allergen-specific IgE (allergy testing) • Atopic dermatitis is almost always a lifelong
type 2 helper T lymphocyte (T H2) immu- • Should be performed only when the diagnosis problem, and the goal is to eliminate or
nologic response (resulting in high levels of of atopic dermatitis is supported by history, minimize allergen exposure while maintain-
IgE). clinical presentation, dermatologic findings, ing the pet’s comfort and homeostasis of the
• Predisposed patients percutaneously absorb and ruling out other differential diagnoses skin.
allergens that provoke the production of • Allergy tests do not diagnose allergy; they • Appropriate clinical protocol depends on the
allergen-specific IgE. only document sensitization, which may have seasonality of the problem, distribution and
• Inhalation or ingestion of allergen may be no clinical significance. severity of lesions, concurrent health issues,
of lesser significance. • Allergy testing is available as an intradermal patient and client compliance, and cost and
• After a sensitization phase, epidermal test performed by veterinary dermatologists availability of therapy. It typically requires
Langerhans cells capture allergens with or as a blood test (serologic testing offered adjustment over time.
antigen-specific IgE, provoking a storm by numerous commercial laboratories). • Allergen avoidance is ideal but rarely
of cytokine and chemokine release from Regardless of method, test results must be possible.
keratinocytes, mast cells, and infiltrating reviewed in light of allergen exposure and • Although ASIT is the sole therapy inducing
eosinophils, neutrophils, allergen-specific the patient’s history. immune tolerance to the offending allergens,
T H 2 lymphocytes, and dermal dendritic cells. • Intradermal testing: considered gold standard, additional antipruritic therapy is often required.
• Dogs and cats are most commonly sensitized but animals must be clipped and sedated. • Secondary yeast and bacterial infections
to house dust and storage mites, molds, • Serologic testing: false-positives are common should be controlled by appropriate therapy
pollens, and danders. but more convenient and less affected by before any attempt is made to further control
• Malassezia antigens may represent major antipruritic therapies. No clinical correlation pruritus.
allergens, but staphylococcal antigens are not associated with the number and magnitude • Antiparasitic preventives should be adminis-
currently proven to have a role. Both of positive reactions. tered to avoid pruritic parasitic infestation.

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