Allergic Disease Objectives
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- Describe the pathogenesis of atopic dermatitis.
- Atopic dermatitis is “strange disease†and is a familial predisposition to the development of IgE antibodies and clinical allergy to environmental antigens
- Describe the lesions and distribution pattern of atopic dermatitis
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Lesions:
-Erythema
-Alopecia
-Papules
-Excoriations
-Hypepigmentation
-Lichenification
Distribution:
-Muzzle
-Periocular
-Axillae
-Feet
-Flexor surfaces of elbows and tarsus
-Extensor surface of carpus
-Lesions may become generalized in chronic cases - What are the advantages and disadvantages of RAST?
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Advantages
-Very specific
Disadvantages
-Poor reproducibility
-Poor specificity for IgE
-Many false positives
-Great seasonal variability - What are the advantages and disadvantages of IDST?
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Advantages
-Gold standard for determining allergens
-Shows whether or not an allergen is capable of producing skin lesions in the tested patient
-Immediate results
Disadvantages
-Owners refuse clipping of fur
-If skin does not respond to the histamine, it won’t respond to injected allergens
-No access to the test - How do you interpret a negative IDST?
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-Patient not allergic to reaction
-SQ injection given
-Insufficient antigen
-Concurrent drugs blocked the skin test (this is why they must be off drugs before testing)
-Prolonged allergy (exhaustion of IgE levels) - How do you interpret a positive IDST?
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-Patient allergic to antige
-Patient allergic to the cross reacting antigen
-Irritants
-Bacterial or fungal contamination
-Antigen contains histamine
-Too large volume injected - What are the advantages and disadvantages of using corticosteroids for the treatment of atopic dermatitis?
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Advantages
-Very effective at decreasing skin inflammation and itching
Disadvantages
-Many side effects (PUPD, panting, weight gain, increased risk of infection, ect.)
-Use only if other therapies are not feasible - What are the advantages and disadvantages of using cyclosporine for the treatment of atopic dermatitis?
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Advantages
-Effective in severe allergy cases for decreasing skin inflammation and itching
-Suppresses T cells and decreases IgE production
-Decreases production of cytokine
Disadvantages
-Side effects (GI, renal, hepatic, bone marrow)
-Costly - What are the advantages and disadvantages of using hyposensitization (immunotherapy) for the treatment of atopic dermatitis?
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Advantages
-Increases T suppressor cell activity, w/ gradual decrease in IgE
-Blocks antibodies
-Decreases number of mast cells and/or decreases histamine release from mast cells
Disadvantages
-May req. 9 months or longer to obtain maximal effectiveness
-25-50% chance of not working or needed additional treatment - Discuss client education of the treatment of atopic dermatitis.
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-Must communicate that the animal is a walking dust mite and they must be bathed frequently
-Also, if animal is allergic to material in house or what owner wears, significant changes must be made
-Owner must be committed to working w/ the disease or the animal will suffer for their entire life - Describe the MOA of glucocorticoids in treatment of allergy.
- -Glucocorticoids block Cox 1 and 2 as well as phospholipase A (which is needed to make Prostaglandins)
- Describe the benefits of antihistamines in cats and dogs
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-Antihistamines are a good preventative drug, just not great for treatment
-Block H1 and H2 receptors
-Stabilize mast cells
-Few side effects - Describe the physiological basis of alternate day steroid administration.
- -Alternate day therapy is an attempt to control the animals atopy while giving them less drug. This will decrease the potential for side effects and resistance.
- Are lamb and rice nonallergenic?
- -NO- lamb and rice are not non-allergenic (many animals are, in fact, allergic to lamb)
- Why are lamb and rice chosen for some hypoallergenic diet trials?
- -Lamb and rice are chosen however for some hypoallergenic diets b/c lamb is a novel protein and if the animal has never tried lamb it might be worth a try. Rice is added in as the carbohydrate source
- Devise a restrictive diet trial for a cat or dog for which you have been presented with a list of its past diet.
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HOME COOKED DIETS
-Choose a protein source that the animal has never been exposed to (lamb, fish, venison, rabbit, tofu, pinto beans)
-Choose a carbohydrate source (brown rice, white rice, potatoe, green peas)
-Mix the two as a 1 part protein : 3-4 part carbo
STORE DIETS
-Again look for a protein source the animal hasn't tried (Hill D/D, Z/D or Purina HA) - What are the DDX of a cat w/ pruritis on its head and neck.
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-Food allergy
-Ear mites
-Notoedres
-Flea allergy dermatitis - How can you differentiate allergic contact dermatitis from an irritant contact dermatitis?
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Allergic Contact dermatitis:
-An inflammatory skin disease caused by a delayed (cell-mediated) response to an antigen or hapten. Requires repeated or continuous exposure to the substance
Irritant Contact Dermatitis:
-An inflammatory skin disease which occurs within minutes of contact w/ irritating substance - Outline measures that can be used to minimize an animals exposure to housedust mites.
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-Remove carpets, blinds, plants, upholstered furniture, cluster
-Use plastic encasings for mattresses, boxsprings, pillow
-There are some products to kill HDM - Describe the clinical presentation of erythema multiforme.
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-Erythematous macules and papules that spread
-Urticarial plaques that last for many days
-Vescilces/bullae
-Any combo of these - Describe the clinical presentation of Toxic Epidermal Necrolysis.
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-Vesicles/bullae
-Necrosis
-Systemically ill
-Entire epidermis of the lesion can be necrotic and slough off - What are the usual causes of Toxic Epidermal Necrolysis.
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-Drugs***
-Toxins
-Infections
-Neoplasms - What are the usual causes of Erythema Multiforme.
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-Drug allergies ***
-Trimethoprim/sulfa
-Cephalexin - What are some etiologies for feline miliary dermatitis?
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-Ectoparasites
-Dermatophytes
-Allergies
-Nutritional
-Bacterial
-Contact
-Autoimmune
-Idiopathic - What is a diagnostic plnn for feline miliary dermatitis?
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-Examine for parasites
-Woods light
-DTM culture - What is the clinical presentation of an indolent ulcer?
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-Ulcers on upper lip or orally
-Female cats (5-6 yrs. Age)
-No eosinophils - What is the clinical presentation of an eosinophilic plaque?
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-Well circumscribed, raised, ulcerative plaque
-Abdomen, back, legs, head, neck
-Female cats (3yrs)
-Eosinophilic and mast cell infiltration - What is the clinical presentation of a linear granuloma?
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-Linear tract on posterior aspect of hind limbs
-Severe cases can be seen in the oral cavity
-Either sex (1-5yrs)
-+/- Eosinophils - How would you identify an indolent ulcer?
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-Histopath
-Hyperplastic ulcerative dermatitis w/ PMN, plasma cells, mononuclear cell infiltrate
-DDX
-Squamos cell carcinoma and Fibrosarcoma - How would you identify an eosinophilic plaque?
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-Histopath
-Eosinophilic and Mast cell infiltrate
-Workup
-Biopsy
-Flea control***
-Hypoallergenic diet
-IDST - How would you identify a linear granuloma?
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-Histopath
-Necrobiosis of collagen w/ histiocytic and multinuclear giant cell infiltrate +/- eosinophils - How would you treat an indolent ulcer?
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-Identify and treat underlying cause
-Antibiotic trial
-Clavamox or Tribissen
-Systemic Corticosteriods
-Pred
-Depo-Medrol
REFRACTORY OR RECURRENT:
-CO2 laser
-Radiation treatment
-Cyrosurgery
-Immuno-stimulants (Levamisole or Thiabendazole) - How would you treat an eosinophilic plaque?
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-Identify and treat underlying cause
-Elizabethan collar
-Antibiotics
-Corticosteriods - How would you treat a linear granuloma?
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-Observation
-Identify and treat underlying cause
-Antibiotics
-Corticosteriods
-Immuno-stimulants - Describe the clinical presentation of feline plasma cell pododermatitis.
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-Non-painful swelling of footpads that may ulcerate
Clinical Pathology:
-Hypergammaglobuinemia
-Lymphocytosis
-Neutrophillia - List the potential side effects of progesterone therapy.
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-Hyperglycemia (leading to DM)
-Acromegaly
-Mammary hyperplasia (leading to neoplasia)
-Pyometra
-Infertility
-Behavioral changes - What is cyclosporine? What is its MOA in the treatment of atopy?
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-Cyclosporine is an immuno-suppressive drug.
MOA:
-Suppresses T helper cells
-Decreases IgE production
-Decreases production of cytokines
-Overall decreases skin inflammation and itching - How is canine atopic dermatitis diagnosed?
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-Must have at least 3 of the Major Criteria:
-Pruritis
-Typical morphology and distribution
-Involves face, feet, legs
-Seasonal or chronic dermatitis
-Family or breed predisposition
-Must have at least 3 of the Minor Criteria:
-Onset of symptoms <3 years of age
-Facial erythema and chelilitis (inflammation around lips)
-Bilateral conjunctivitis
-Superficial staph pyoderma
-Increased antigen specific-IgE
-Increased antigen-specific IgG4
-Immediate skin test reactivity - Is it possible to cure an atopic dog?
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-No, just medically manage dog
-However, those animals treated w/ hyposensitization 25% may develop complete remission - What are the major causes of treatment failures in canine atopic dermatitis?
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-Client compliance
-Don’t remove all possible environmental contaminants
-Don’t dose animals med’s correctly - What is the “flare factor†relating to atopy?
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-The reaction that occurs in response to certain allergen
-Fleas are a big flare factor - Why is it important for owners to understand the concepts of summation of effects and pruritic threshold.
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Summation of effects:
-It is the culmination of all things that can lead to the animals atopy problem
-If the owner can understand that there are a whole host of things that play a role in their animals atopy then maybe then can understand why treatment is so difficult and why they must play an active role in the process.
Pruritic Threshold:
-The level above which the animal will experience atopy
-Many factors contribute the animal exceeding the threshold
-For example: If fleas are the underlying cause and they are never treated, then the animal can never drop below the pruritic threshold - What are the causes and pathogenesis of food allergies?
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Causes:
-Sudden reaction to a food source (usually one protein) that triggers an immunological response
-a lot are not IgE mediated
Patho:
-Food allergies can be either a Type I, III, IV hypersensitivity reaction - What is the best way to diagnose a food allergy
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-The best way to diagnose food allergy is to do a restrictive diet trial
-Symptoms should subside off food (w/in at least 7 days)
-Challenges should be reproducible (onset, duration, clinical features)
-Symptoms should be gone after each withdrawal - What is an allergen? Antigen?
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Allergen: an antigen that stimulates an IgE response (ex. Pollens, dust, animal dander, feathers)
Antigen: a substance that elicits an antibody response - How does contact hypersensitivity manifest in animals?
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-Lesions usually occur in non-haired areas (feet, ears, ventrum, scrotum, chin, neck)
-Pruritis may be the only sign
-Severe cases: erythema, vesicles, ulcers, crusts, self-trauma - What are the differences between atopy and contact dermatitis?
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Atopy:
-A familial predisposition to the development of IgE antibodies and clinical allergy to environmental allergens.
Contact dermatitis:
-Can either be allergic or irritant
Allergic Contact dermatitis:
-An inflammatory skin disease caused by a delayed (cell-mediated) response to an antigen or hepten. Requires repeated or continuous exposure to the substance
Irritant Contact Dermatitis:
-An inflammatory skin disease which occurs within minutes of contact w/ irritating substance - What are the common causes of contact hypersensitivity in dogs?
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-Plant or plant pollen
-Molds
-Meds (neomycin, tetracain, shampoos, insecticides)
-Floor wax
-Polish or cleaners
-Dyes in rugs
-Carpets, blankets
-Rubber and plastic products - Will anti-histamine creams lessen inflammation in animals w/ contact hypersensitivity? What other treatments would you recommend?
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-No anti-histamine are good are prevention, not a treatment once the animal is inflamed
Other treatments:
-Remove offending agent
-Bath after exposure
-Topical drying agents (Domeboro)
-Topical or systemic corticosteroids
-Pentoxiphylline
-Topical tacrolimus - What is miliary dermatitis?
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-Variable pruritic papulocrustous eruption occurring over dorsum, head, and neck
-Millet seed lesions = hemorrhagic crusts - What approach would you follow in treating a cat w/ miliary dermatitis?
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1. Flea control (if they respond, may be the only treatment)
2. Hypoallergenic diets
3. Skin biopsy
-Allergic = IDST
-Bacterial = C/S and TX
-Fungal = DTM and TX
-Pemphigus = DFA, TX
-Non-specific = Pred
-No response = Short term megesterol acetate - What is erythema multiforme?
- it is an allergy, usually drug associated
- How do you diagnose erythema multiforme?
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-Physical Exam
-Clinical signs - How do you treat erythema multiforme?
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-Removal of drug
-Possible corticosteroids?? - What is toxic epidermal necrolysis?
- full thickness coagulation necrosis of epidermis
- How do you diagnose toxic epidermal necrolysis?
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-Histopath
-full thickness coagulation necrosis of epidermis - How do you treat toxic epidermal necrolysis?
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-Correct underlying cause
-Supportive care
-Pred (be careful there can be a high risk of sepsis)