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Atopic Eczema

Symptoms : · Onset usually 2 – 6 months, · Acutely: o Itchy o Redness, swelling, usually ill-defined border

Atopic Eczema

 

·        See topic : Allergy and Hypersensitivity Disorders

 

Symptoms

 

·        Onset usually 2 – 6 months

·        Acutely:

o  Itchy

o  Redness, swelling, usually ill-defined border

o  Papules, vesicle, extremely large blisters, may look weepy

o  Exudates and crusting

o  Scaling

o  Can be papular

·        Chronic:

o  Less vascular and exudative

o  More scaly, pigmented and thickened

o  Fissuring 

o  More likely to be lichenified (epidermal thickening with exaggeration of skin markings) and develop painful fissures

o  If dark skin: post inflammation change in pigmentation

o  Pitting of nailed if involved with ridging of nails

·        In babies:

o   Common onset in first few weeks

o   Quite weepy/blistery 

o   Around face (spares eyes and base of nose) and trunk. If extensor distribution think of contact sensitivity (eg house dust mite)

o   Can be due to antigens in breast milk 

o   The itch that rashes: itchy skin is scratched and an eruption occurs – don‟t see rash where child can‟t reach

·        Children, and older:

o   Bends of elbows, behind knees

o   More leathery

o   Between big toe and 2nd toe (compared with tinea between 4 and 5)

·        Associated with asthma and hay fever

·        Associated with food allergy – commonly cows milk but this is overstated

·        Atopic skin has lower threshold to irritation (eg soaps) and is more prone to staph infection

·        Prognosis: ½ have cleared by 12, few persist after age 30

·        Increased tendency to: dry skin, urticaria, pityriasis alba, keratosis pilaris, irritant contact dermatitis, etc

 

Pathogenesis

 

·        Genetic predisposition

·        ?Imbalance of Th1 and Th2 cells in the thymus in favour of Th2 

·        ?Early childhood infections ® preferential induction of Th1 type cytokines and prevent atopic sensitisation. ¯Infections ® greater risk of atopy 

·        Inversely proportional to the number of older siblings (marker of exposure to infection)

·        Atopy does not equal allergy:

o   Level of IgE, which may be elevated, doesn‟t correlate to severity 

o   Up to 50% of children with eczema do not have +ive skin prick tests (especially if mild eczema and no asthma) 

o   Skin prick tests for histamine release (type 1 reaction) may be positive but the person may have not reaction when exposed to that allergen

o   Rast test looks for antigen specific IgE

o   Type 1: normally asthma, rhinitis, urticaria, not usually eczema

o   Patch testing (Type 4) may be relevant to childhood eczema 

o   Only 50% with severe eczema develop reactions when challenged with particular foods – most are delayed reactions

·        See Allergy and Hypersensitivity Disorders

 

Management

 

·        Investigations

o   Patch testing 

o   Is there infection? (Yellow crusts, weepy, failure to respond to treatment) ® systemic antibiotics

·        Prevention:

o   Don‟t itch

o   Avoid aggravators:

§  Light cotton clothes, no scratchy woollens

§  Avoid excess humidity/dryness

§  Avoid local or systemic aggravators

§  Care with soaps, perfumes, solvents etc

§  Baths not shower, not too hot, pat not rub dry

§  Reduce stress

o   Control dry skin: Emollients – aqueous cream, white soft paraffin

·        Medical:

o   Topical corticosteroids:

§  Reduce inflammation but doesn‟t treat cause

§  Use weakest possible – 1% hydrocortisone OK for most

§  At night use in conjunction with wet dressings (containing emollient) 

§  Not for too long otherwise skin atrophy, striae and rebound afterwards, wrinkling, ­vascular markings, also dynamite to viral/bacterial infections. Even worse with systemic steroids

§  Lotion for scalp, ointment for dry areas (may cause folliculitis), cream

o   Strength:

§  Face and flexures: mild only 

§  Scalp, palms and soles: can tolerate very potent steroids (eg betamethasone diproprionate) 

§  Body and limbs: potent for short periods (a week or two), mild to moderate as maintenance

o   Systemic steroids for severe eczema, for a short time only

·        Tar compounds: esp. at night to prevent itching

·        Antihistamines: stop itching (more in kids and for sedative effect) and urticaria

·        Antibiotics for infection

·        For severe eczema: phototherapy, azathioprine, cyclosporin

 

Allergy and Hypersensitivity Disorders

 

Hypersensitivity 

·         A lay term

o   Stimuli that don‟t cause symptoms amongst general population

o   Usually reaction of body surfaces (eyes, airways) to environmental factors

·         Autoimmune disease can be any one of types II, III or IV 

·         Hyperreactivity = ­ sensitivity to non-specific stimuli (= irritants), eg cold, perfumes, etc

Allergy

·         = Immunologic reaction to common substances which are harmless to most people 

·         Previous exposure ® antibodies or specific lymphocytes against these substances

·         Types:

o   Atopy: 

·         Predisposition to produce IgE antibodies to common environmental substances (also called immediate or Type 1 hypersensitivity). 

·         Order of incidence:

§  Adults aged 20 – 44 in New Zealand: Asthma 15%, hay-fever 35%, Maori more symptomatic 

§  Mediators lead to vasodilation, vascular leakage (swelling), smooth muscle spasm (eg respiratory). 

§  Similar symptoms can occur from non-allergic hypersensitivity => non-atopic 

o   Contact Allergies: direct skin contact with nickel, chrome, rubber. Due to lymphocyte (delayed-type hypersensitivity, type IV) not IgE antibodies 

o   Allergic Alveolitis ® lung inflammation. Eg farmer‟s lung, pigeon fancier‟s lung. Due to lymphocytes and IgG (not IgE) 

·         Risk factors: 

o   Allergy predominates in young adults and children: while non-specific hypersensitivity is more common later in life 

o   Genetic Factors: One parent ® doubled risk of child having atopic disease. Both parents ® 4 times risk 

o   Early childhood factors important in subsequent development of allergic disease: 

§  High house dust mite/cat/pollen exposure in early months ® ­risk

§  Exposure to tobacco smoke in utero/infancy ® ­risk 

§  Early life infections ® ¯risk: ?improved shift from TH2 environment of uterus to non-allergic TH1 immune responses which dominate in most infections (especially intracellular pathogens) 

§  First born children at greater risk

o   The workplace is a major source of allergen exposure

·         Bee sting allergy:

o   Don‟t have to have atopic history

o   If anaphylaxis as a child, 1 in 6 chance next time.  For adult, 60% chance next time 

o   Carry adrenaline until desensitisation (serial antigen shots ® 95% effective) 

o   Anaphylaxis: give 0.5 m of 1:1000 adrenaline IM if in community setting (iv in hospital if you can give slow infusion). IM gives good diffusion, safer, effective and fewer problems with cardiac vasoconstriction cf bolus 


 

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