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65 Cards in this Set
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synonyms canine atopic dermatitis
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- canine atopy
- canine atopic disease - CAD |
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def: canine atopic dermatitis
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a genetically predisposed inflammatory and pruritic skin disease with characteristic clinical features associated with IgE Abs most commonly to environmental allergens
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why do animals develop CAD
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- impaired skin barrier function associated with abnormal fillagrin and lowered amounts of ceramides in their surface lipid which facilitates allergen penetration
- they have a Th1/Th2 imbalance that favours the development of IgE |
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allergens involved with CAD
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- house dust mites (Dermatophagoides farinae and pteronyssus and Bloomia tropicalis in tropical climates) - live on human and canine dander and are the most common allergens involved
- food storage mites (Acaris siro and Tyrophagus putrescentiae). significant cross-reactivity between these and house dust mites - pollens of grasses, weeds and trees - human and feline dander - mould allergens less commonly |
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route of access of allergens with CAD
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- allergens gain access mainly through the skin, aided by Langerhan's cells within the epidermis that are armed with IgE antibody
- ingestion or inhalation of allergen can also cause disease |
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inflammatory mediators in CAD
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IgE antibody attaches to mast cells and to blood basophils bia high affinity Fc receptors. Upon access of allergen a number of mediators are released, both preformed and newly generated
- preformed = histamine, heparin, serotonin, proteinases - newly generated = platelet activating factor, prostaglandins, thromboxanes, leukotrienes - also likely that interleukins derived from keratinocytes have a proinflammatory role as does TNF-alpha |
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preformed inflammatory mediators
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- histamine
- heparin - serotonin - proteinases |
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newly generated inflammatory mediators
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- platelet activating factor
- prostaglandings - thromboxanes - leukotrienes |
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inheritance of CAD
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- unclear although genetic abnormalities associated with the condition have been documented and certain breeds are over-represented
- poodles of all types and mixed breed dogs appear to be protected against the disease and the incidence is lower than expect |
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age of onset of CAD
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peaks between 1 and 2 years with 16% starting before 1 year.
never starts below 3 months, rarely before 6 months or after 7 years |
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CS of CAD with primary disease
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- primarily dermatological +/- hay fever signs
- allergic asthma rarely/never occurs - pruritus is the cardinal sign (99%) - predominantly facial, ventral and pedal distribution but may cause generalised disease - otitis externa in almost all cases at some point affecting initially predominantly the inner surface of the ear flap and the vertical canal |
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secondary complications from CAD
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- generalised recurrent pyoderma: usually a folliculitis but occasionally a deep pyoderma (because self-trauma disturbs the natural barrier, seborrhea leads to colonisation with staphylococci, atopic dogs have impaired CMI)
- bacterial overgwoth without epidermal invasion: leads to exotoxin release and maybe the dvt of staphylococcal IgE compounding the disease process - proliferation of Malassezia which can add to the pathogenesis through its IgE - otitis may become complicated by secondary bacterial and/or yeast infection which may involve the horizontal ear canal - variety of changes resulting from self-trauma - chronic skin changes including seborrhoea, hair loss, generalised erythema, hyperpigmentation and lichenification |
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Dx CAD
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- compatible clinical signs
- absence of other explanations for CS - evidence of allergen-specific IgE through skin tests or in vitro tests - correlation between the presence of allergen specific IgE and the presence of the allergen in the environment |
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CAD rule-outs
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- parasitic disease: especially scabies, cheyletiella, trombicuka and flea allergy
- food allergy: can co-exist and appear very similar - contact allergy: ALWAYS a macular/papular eruption and restricted to the hairless areas |
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demonstration of allergen-specific IgE
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- intradermal skin tests
- serological tests (ELISA) |
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chars intradermal skin tests for demonstration of allergen-specific IgE
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- preferred approach but not applicable in routine general practice
- ensure patient is off antihistamines for 10 days and off corticosteroids for at least one week for every month of therapy (topic, ophthalmic and otic) |
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chars serological tests for demonstration of allergen-specific IgE
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- antihistamines have no effect
- corticosteroids have less effect: it is ok to submit samples whilst on low doses - ELISA test uses an enzymem labelled anti-canine IgE to detext allergen specific IgE |
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problems with demonstration of allergen specific - IgE
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- the presence of a positive skin test or of a positive serological test does not of itself justify a diagnosis of atopic dermatitis: merely support such a diagnosis
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therapy of CAD
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- lige-long therapy required (10-20% may cure spontaneously or be "cured" with immunotherapy"
- develop a plan for both the primary and the secondary complications |
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key points of hyposensitisation (immunotherapy)
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- cornerstone of therapeutic approach (although concomitant medical therapy including corticosteroids is usually given)
- MOA via upregulation of Treg cells - not indicated where there is a short season of involvement or in old animals |
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selection of antigens for hyposensitisation/immunotherapy
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most dermatologists limit the mixture to 10 allergens and if animal is multisensitive either include only those to which strong reactions occured or ithat are prevalent in the environment or make up 2 vaccines and administer alternatively
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types of preparations available for hyposensitisation (immunotherapy)
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- aqueous extracts
- alum precipitated (Europe) |
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side effects of hyposensitisation/immunotherapyffor CAD
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- anaphylaxis
- exacerbation of pruritus |
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expected results from immunotherapy/hyposensitisationffor CAD
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- 60% of dogs will improve by >50%
- 20% of placebo dogs also improve indicating a tendency for spontaneous improvement in a minority of untreated cases - response to hyposensitisation based upon results of skin tests is similar to that based on results of in vitro tests - random hyposensitisation with a standard mixture of allergens is generally ineffective, implying that correct selection of allergens is necessary for success |
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allergen eviction for treatment of CAD
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- cats, birds or other animals
- human dander (high in bedrooms) - storage mites (avoid stale dried foods, keep food tightly sealed and in a cool dry environment) - wool rugs - house dust mites (parasiticides and insect growth regulators are effective) |
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medical therapy against the primary disease to treat inflammation due to allergen/IgE interaction in CAD
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- corticosteroids: parenteral, topicals, antihistamines
- essential fatty acids - Misoprostol (PGE analogue) - Cyclosporine A - interferon |
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medical therapy to treat the barrier function of primary disease in CAD
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- ceramide-containing shampoos or precursors
- Allerderm Spot which contains ceramides |
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medical therapy against the secondary disease of CAD
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- antibiotics or antibacterial shampoos are indicates in cases of bacterial overgrowth or overt pyoderma
- anti-yeast therapy in cases of Malassezia overgrowth |
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chars canine food allergy
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- reactions occur through immunological reactions (hypersensitivity) or non-immunological reactions (food intolerance)
- unclear pathogenesis but IgE and I?gG antibodies and cell mediated hypersensitivity could be relevant - can present with GI, derm or combo sings - occurs with 30% of atopic dermatitis - no reporte dinherited predisposition although some breeds are predisposed |
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CS of canine food allergy
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- GI signs: diarrhea, vomiting, eosinophilic gastroenteritis and/or lymphocytic-plasmacytic enteritis
- dermatological signs: pruritus, half the cases start <1 yr, usually papules with secondary staph infection and relapses quickly after antibiotic therapy - recurrent otitis externa in >80% of cases commencing in the horizontal canal - almost indistinguishable from atopic dermatitis |
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Dx of canine food allergy
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- intradermal skin test (unreliable)
- in vitro test for allergen specific IgE/IgG - hypoallergenic diet trial "gold standard": home-prepared, commercial single-source protein, dydrolysate diet and confirming with refeering original diet and seeing relapse |
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Chars allergic contact dermatitis
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- irritant contact or allergic contact (can overlap)
- antigens are usually simple chemicals that become complete antigens on union with host protein - Langerhans' cells are involved with antigen presentation and cell0mediate hypersensitivity (type 4) - inside allergens implicated include detergents, dyes and anti-oxidants used in carpet manufacture - external allergens include grasses, weeds, weed killers and fertilizers - foliage more allergenic when recently cut or wet - seen almost exclusively in the dog, with occasional cases in horses - uncommon |
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CS allergic contact dermatitis
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- restricted to hairless parts of the body
0 usually a clear demarcation between involved and uninvolved skin - primary eruption is maculopapular - always pruritic but variable - varietty of changes result from self trauma - hyperpigmentation and lichenification in chronic cases - often a secondary staphylococcal infection restricted to the involved area (cf. atopy and food allergy) |
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Dx allergic contact dermatitis
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- confirmation of the Dx: histopath changes of early lesions, selective environmental change, complete change in environment (will also improve atopic dogs)
- implication of the allergen: environmental challenge, patch tests |
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therapy allergic contact dermatitis
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- remove allergen from environment
- remove pet from environment - if impossible: corticosteroids |
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Chars hymenoptera hypersensitivity
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- wasps, bees and hornets involved
- can get a fatal anaphylactic reaction mediated by IgE - severe local swelling through angioedema which may be life threatening in the oropharyngeal region - IV epinephrine with IV corticosteroids used for anaphylaxis - injectable corticosteroids for angioedema - similar reactions may be seen in fire ant hypersensitivity |
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miliary dermatitis
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- primary lesions in cats is erythematous papule that readily becomes necrusted
- multiple lesions may be found at any part of the body - often more readily appreciated by palpation |
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differentials for miliary dermatitis in cats
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- when larger crusted lesions develop the can resemble pemphiguis foliaceous
- but miliary lesions are very characteristic |
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aetiologies of miliary dermatitis
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- atopic dermatitis
- food allery - lice - bacterial folliculitis - trombicula - flea allergy - dermatophytosis - cheyletiella - idiopathic |
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therapy for miliary dermatitis
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- identify and treat cause
- for idiopathic cases or symptomatic therapy: corticosteroids or megesterol acetate |
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side-effects of megestrol acetate
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- polyphagia
- polydypsia - personality changes - endometritis/uterine stump abscess - adrenocortical suppresion - diabetes mellitus - mammary hyperplasia - mammary carcinoma |
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clinical features of head and neck pruritus
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crusting lesions with self-excoriation centred around the head and neck
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aetiologies of head and neck pruritus
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- food allergy more likely than atopic dermatitis with this reaction pattern
- notoedres - some cases of autoimmune disease pemphigus foliaceous |
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therapy for head and neck pruritus
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identify and treat the specific disease
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clinicopathological features of eosinophilic plaque
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- cats!
- well-demarcated, raised, ozzing and ulcerated plaques - random distribution but have a predilection for the abdomen and medial thighs - lesions highly pruritic and may be regional lymphadenopathy - marked peripheral and tissue eosinophilia |
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differentials for eosinophilic plaques
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- bacterial and fungal granulomas
- mast cell tumours - lymphomas, particularly mycosis fungoides |
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aetiology eosinophilic plaques
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- flea allergy
- atopy - idiopathic - food allergy - any cause of excessive licking (autoimmune?) - bacterial infection |
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therapy for eosinophilic plaques
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- identify and treat cause
- corticosteroids for idiopathic cases |
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clinicopathological features of linear granuloma (collagenolytic granuloma
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cats! 3 forms are histologically similar and manifest collagenolysis
- linear nodules usually affect the posterior aspect of one or both hindlimbs - nodular lesions with a verrucose appearance in the mouth - swelling on the chin - marked tissue eosinophilia and sometimes peripheral eosinophilia |
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differentials for linear granuloma (collagenolytic granuloma)
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- differentials for oral form include various neoplasms
- chin form should be distinguished from infected acne - linear form is so characteristic as to have no other significant differentials |
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aetiology of linear granuloma (collagenolytic granuloma)
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less reliably associated with allergy, often a cause cannot be found
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therapy for linear granuloma (collagenolytic granuloma)
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therapy for idiopathic cases largely consists of corticosteroids
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clinicopathological features of eosinophilic (indolent) ulcer
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- incorrectly named "rodent ulcer"
- cats! 0 ulcerated lesion of the upper lip - occasionally may occur on other parts of the body - peripheral and tissue eosinophilia are not a feature |
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differentials for eosinophilic (indolent) ulcer
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- SCC for the lip form
- ulcers of infective origin and mast cell tumours for other forms |
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aetiology of eosinophilic (indolent) ulcer
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- associated with allergy - including flea allergy
- may be a bacterial component - possibility of an autoimune component (pemphigus) - 25% are idiopathic |
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therapy for eosinophilic (indolent) ulcer
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- identify and treat cause
- parenteral or intralesional corticosteroids - antibiotics may help in some cases |
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clinical appearance of self-induced hair loss "barbered alopecia"
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- usually symmetrical involving the flank and ventrum
- short stubbly hairs left behind - shorn-off tips of hair shafts |
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aetiology of self-induced hair loss/barbered alopecia
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any of the allergic skin diseases
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therapy for self-induced hair loss/barbered alopecia
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identify and treat cause
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chars feline atopic dermatitis
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- less well characterised than the canine disease
- not clear that it is an inherited disease |
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CS feline atopic dermatitis
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- pruritus is cardinals ign
- some cats may suffer from concomitant feline asthma - affected cats may show combination of: self-induced hair loss, miliary dermatitis, eosinophilic plaques, eosinophilic ulcers and linear granulomas (less reliably associated) |
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Dx feline atopic dermatitis
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- comaptible CS
- absence of any other explanation for those signs - demonstration of allergen-specific IgE byu intradermal skin trsting and in vitro tests employing antifeline IgE or the Fce recetor a-chain which cross reacts |
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therapy feline atopic dermatitis
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- hyposensitisation
- corticosteroids - chlorphenarimine (most effective antihistamine for cat) |
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chars feline food allergy
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- CS very similar to those of atopic dermatitis but GI signs may coexist
- 33% of cases have lesions restricted to the head and neck - diagnostic approach is as for the dog, taurine supplementation not needed if fresh meat is used but if home-prepared diets are used for long-term control |
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contact allergy in cats
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- rarely if ever seen in cats
- reactions to flea collars have been reported but whether this is irritant or allergic is not known |
