ALLERGIC DERMATOSES : ATOPIC DERMATITIS - CANINE
- AT A GLANCE
- WHAT DOES IT LOOK LIKE?
- WHAT ELSE LOOKS LIKE THIS?
- HOW DO I DIAGNOSE IT?
- HOW DO I MANAGE IT?
- COMMENTS
What Is It?
- A genetically predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features associated with IgE antibodies most commonly directed against environmental allergens
- Mode of inheritance is unknown; environmental factors may be important in the development of the disease
- Defects in the skin barrier may play an important role in allergen exposure
- Allergens are absorbed through the skin and captured by cutaneous Langerhans cells which present them to T-helper 2 lymphocytes in the dermis. This results in release of inflammatory mediators, cytokines that increase allergen-specific IgE as well as cytokines that cause direct neuronal stimulation and itch
- (Link to www.itchcycle.com MOA videos)
What Does It Look Like?
- Can occur in any breed of dog but is more commonly diagnosed in the terrier breeds (West Highland White, Cairn, fox terrier, etc), golden retriever and setters
- Mean age of onset is 1-3 years but may begin as early as 6 months of age
- May be seasonal or year round
- Estimate that 8% of dogs have AD
- The major clinic feature is pruritic behavior – scratching, rubbing, licking, chewing
- The pruritus responds to treatment with glucocorticoids
- Primary lesions are rare and most of the clinical signs are secondary to self trauma
- Most commonly affected areas are the periocular, perioral, caudal carpus and tarsus, inner pinnae and axillae
- Secondary skin infections with Staphylococcus and Malassezia are common
What Else Looks Like This?
- Other allergic and pruritic dermatoses
- Food allergy (cutaneous adverse reactions to food)
- Flea bite hypersensitivity
- Sarcoptic mange
- Pruritic pyoderma
- Malassezia infections
How Do I Diagnose It?
- The diagnosis of AD is made by exclusion of other causes of pruritic dermatitis
- Intradermal testing or measurement of serum allergen-specific IgE is used to select allergens used for hyposensitization (see below), not to make the diagnosis
How Do I Treat It?
- JAK Inhibitor
- A different class of medication that specifically targets the cytokines involved in itch and inflammation associated with allergic skin conditons with minimal negative impact on immune function
- Monoclonal antibody
- Caninized monoclonal antibody (mAb) targeting interleukin-31 (IL-31): aids in the reduction of clinical signs associated with atopic dermatitis in dogs. IL-31 has been shown to induce pruritus in dogs in laboratory studies
- Corticosteroids
- Provide rapid relief from itching and control of inflammation
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- prednisone (prednisolone) – 0.25-0.5 mg/kg PO SID for 3-7 days to start and then tapered to the lowest effective dose
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- Avoid repeated injections of long acting or repository corticosteroids
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- Safe annual dose of prednisone
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- Body Weight (kg) X 30 = mg prednisone / year
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- Antihistamines
- None are approved for use in veterinary medicine
- Evidence-based medicine fails to show that they provide benefit in the treatment of AD
- Cyclosporine
- 5mg/kg PO SID x 30 then decrease frequency
- Fatty acids
- Oral and topical supplementation with ω-3 FAs may help in moderating inflammation and improving the skin barrier
- Topical therapy
- Frequent bathing to remove allergens and control colonization by Staphylococcus and Malassezia
- Immunotherapy (hyposensitization)
- Allergens selected based on the results of intradermal testing or allergen-specific IgE serology
- Injectable or sublingual immunotherapy(SLIT)
- About 2/3 dogs show some response to therapy
- May take up to a year of therapy before improvement is seen
COMMENTS
- Best practices for control of AD are early diagnosis and establishment of a management program
- Controlling flare factors such as skin infections and fleas is essential
- Client education about the pathogenesis and ongoing nature of AD is key to successful management.
- Consider referral to a local dermatologist
References:
- Miller WH, Griffin CE. Campbell K. eds. Muller and Kirk’s Small Animal Dermatology 7th ed. Saunders, 2013: 125. 364-388
- Veterinary Clinical Advisor. Dogs and Cats. Cote.E. 2nd ed. Mosby. 2011: 106-108
- Nuttall T, Harvey RG, McKeever PJ. A Colour Handbook of Skin Disease Of The Dog and Cat. 2nd ed. 2009 Manson Publishing, 20-30.
abscess
A discrete swelling containing purulent material, typically in the subcutis
alopecia
Absence of hair from areas where it is normally present; may be due to folliculitis, abnormal follicle cycling, or self-trauma
alopecia (“moth-eaten”)
well-circumscribed, circular, patchy to coalescing alopecia, often associated with folliculitis
angioedema
Regional subcutaneous edema
annular
Ring-like arrangement of lesions
atrophy
Thinning of the skin or other tissues
bulla
Fluid-filled elevation of epidermis, >1cm
hemorrhagic bullae
Blood-filled elevation of epidermis, >1cm
comedo
dilated hair follicle filled with keratin, sebum
crust
Dried exudate and keratinous debris on skin surface
cyst
Nodule that is epithelial-lined and contains fluid or solid material.
depigmentation
Extensive loss of pigment
ecchymoses
Patches due to hemorrhage >1cm
epidermal collarettes
Circular scale or crust with erythema, associated with folliculitis or ruptured pustules or vesicles
erosion
Defect in epidermis that does not penetrate basement membrane. Histopathology may be needed to differentiate from ulcer.
erythema
Red appearance of skin due to inflammation, capillary congestion
eschar
Thick crust often related to necrosis, trauma, or thermal/chemical burn
excoriation
Erosions and/or ulcerations due to self-trauma
fissure
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
fistula
Ulcer on skin surface that originates from and is contiguous with tracts extending into deeper, typically subcutaneous tissues
follicular casts
Accumulation of scale adherent to hair shaft
hyperkeratosis
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
hyperpigmentation
Increased melanin in skin, often secondary to inflammation
hypopigmentation
Partial pigment loss
hypotrichosis
Lack of hair due to genetic factors or defects in embryogenesis.
leukoderma
Lack of cutaneous pigment
leukotrichia
Loss of hair pigment
lichenification
Thickening of the epidermis, often due to chronic inflammation resulting in exaggerated texture
macule
Flat lesion associated with color change <1cm
melanosis
Increased melanin in skin, may be secondary to inflammation.
miliary
Multifocal, papular, crusting dermatitis; a descriptive term, not a diagnosis
morbiliform
A erythematous, macular, papular rash; the erythematous macules are typically 2-10 mm in diameter with coalescence to form larger lesions in some areas
nodule
A solid elevation >1cm
onychodystrophy
Abnormal nail morphology due to nail bed infection, inflammation, or trauma; may include: Onychogryphosis, Onychomadesis, Onychorrhexis, Onychoschizia
onychogryphosis
Abnormal claw curvature; secondary to nail bed inflammation or trauma
onychomadesis
Claw sloughing due to nail bed inflammation or trauma
onychorrhexis
Claw fragmentation due to nail bed inflammation or trauma
onychoschizia
Claw splitting due to nail bed inflammation or trauma
papule
Solid elevation in skin ≤1cm
papules
Solid elevation in skin ≤1cm
paronychia
Inflammation of the nail fold
patch
Flat lesion associated with color change >1cm
petechiae
Small erythematous or violaceous lesions due to dermal bleeding
phlebectasia
Venous dilation; most commonly associated with hypercortisolism
plaques
Flat-topped elevation >1cm formed of coalescing papules or dermal infiltration
pustule
Raised epidermal infiltration of pus
reticulated
Net-like arrangement of lesions
scale
Accumulation of loose fragments of stratum corneum
scar
Fibrous tissue replacing damaged cutaneous and/or subcutaneous tissues
serpiginous
Undulating, serpentine (snake-like) arrangement of lesions
telangiectasia
Permanent enlargement of vessels resulting in a red or violet lesion (rare)
ulcer
A defect in epidermis that penetrates the basement membrane. Histopathology may be needed to differentiate from an erosion.
urticaria
Wheals (steep-walled, circumscribed elevation in the skin due to edema ) due to hypersensitivity reaction
vesicle
Fluid-filled elevation of epidermis, <1cm
wheal
Steep-walled, circumscribed elevation in the skin due to edema