20. Allergic disorders. Flashcards
what is IgE mediated type 1 allergy?
the allergen taken by antigen representing cell - presenting to Th cell - activating it into a TH2 cell - stimulates B cell to produce IgE antibodies which then goes to mast cells and basophils = sensitisation
next time the allergen directly stimulates the mast cells
Atopy is the genetic predisposition to make IgE antibodies in response to allergen exposure.
Mast cells and basophils have a high affinity IgE cell membrane receptors for IgE
what are the phases in IgE mediated hypersensitivity ?
step 1 - sensitisation
step 2 - early phase within minutes (immediate reaction)
through degranulation os wast cells
step 3 - late phase response
hours
through endothelia cel activation and leukocyte infiltration
what are the symptoms for allergic asthma
asthma - wheezing , dyspnea , tachypnea
route of entry - inhalation
what is the clinical manifestation of atopic dermatitis(eczema)
urticaria (hives , angioedema) ?
atopic dermatitis is chronic
Intense pruritis and dry skin:
in infants most often on cheeks and scalp , wrist , extensor as pects
the nappy area is usually spared
Dennie-Morgan fold: increased folds below the eye
2-12 years - dry itch skin on flexor surfaces of the body - inside of elbow , creases of wrist, back of knee , face , hands, feet
it can then become red , then blister and peel and lichenified
is worst at night (due to no distractions)
teenagers - flexural surfaces , face especially periorbital region , hands and feet
====== prurutic vesicular lesions or pruritic bullous lesions Well-circumscribed, raised, erythematous plaques with a round / oval, / serpiginous shape
Up to several centimeters in diameter (wheals)
angioedema of the laryngopharynx can obstruct airway - difficulty breathing / stridor / hoarseness = life threatening
due to maybe ingestion of foods.
nuts, chocolate, fish, tomatoes, eggs, fresh berries, and milk.
what causes atopic dermatitis
polygenetic inheritance
Mutation in the filaggrin gene → abnormalities in epidermal skin barrier formation → entry and interaction of antigens with immunogenic cells
Triggers Dust mites Heat Extremely dry or humid climate Emotional stress Pollen Pet fur Fabrics Soap
usually people with atopic dermatitis have food allergy.
how do we clinically diagnose atopic eczema / urticaria ?
four criteria is sufficient
pruritus
stigmata of atopy - Typical morphology and age-specificdistribution patterns
early onset
chronic or relapsing course
Exclusion of other cond itions
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igE mediated
atopy- family history
xerosis
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urticaria - fam history
in vivo skin test
Skin prick test
Tiny amounts of various allergens are applied to the skin; a lancet is then used to prick the surface of the skin so that allergen extracts may enter.
Scratch test
Intradermal injection test
in vitro
Tryptase in serum (a relatively specific marker of mast cell activation):.
Allergen-specific IgE
in patients in whom the risk of anaphylaxis is high (ELISA)
Total IgE.
punch biopsy of the lesion should be performed and sent to the pathology laboratory to look for leukocytoclastic vasculitis
how do we treat atopic eczema
Sedat In first generation antihistamines if itchy
primary preventioon f breast feeding
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very mild = emollients ,regular bathing
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mild to moderate
topical steroids
hydrocortisone 1 percent - low potency twice daily
topical calcineurin inhibitors
moderate - severe - non pharmacological - wet wrap therapy
icrease topical potency
medium potency -
triamcinolone 0.1 percent - twice daily
high potency - fluocinomide - 0.05 percent
consider corticosteroid systemic therapy
phototherapy
immunomodulators - cyclosporine
Azathioprin
Mycophenolate ‘
how do we treat urticaria ?
cetirizine - NOT ACUTE
oral (doses given here)
IV - indicated in acute cases aged over 6 months
<5 years - 2.5mg IV daily
<12 years - 5-10mg IV daily
>12 years - 10mg IV daily
IF ACUTE!!! -
diphenhydramine (Benadryl)
IM/IV
1 mg/kg/dose
2-6 years: 6.25 mg q4-6hr
6-12 years: 12.5-25 mg PO q4-6hr
>12 years: 25-50 mg PO q4-6hr
use the liquid or rapid-dissolving tablet
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oral glucocorticoids in acute cases - if urticaria does nt fade in 2hrs with Benadryl
prednisone at a dose of 1 mg/kg/ day
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for chronic idiopathic urticaria- Omalizumab (FDA approved) children over 12 years
150-300mg subcutaneously every 1 month
what is the clinical manifestation of allergic gastroenetropathy ?
committing diarrhoea
what are the triggering factors of anaphylaxis ?
food - 30 min onset of symptoms
insect - 15 min
medication - 5 min
what is the clinical manifestation of systemic hypersensitivity
anaphylaxis -
shock , hypotension ,
flushing
wheezing. dysphasia - angioedema of throat / bronchoconstriction
hoarseness ,
swelling of eyelids , angioedema (urticaria)
chest tightness
nausea , vomitting , diarrhea , abdominal cramping
uterine cramping and urinary urgency
death within 15 minutes
due to insect or venom or drugs such as penicillin
the causes of anaphylaxis are divided into two major groups ?
age mediated
initial sensitising exposure
non ige mediated - do not require ige immune reaction - direct stimulation of mast cells and basophils - no sensitisation is required
what is the management of anaphylaxis ?
call for help , lie the patient flat and raise their legs ( patients should be placed supine or in the Trendelenb urg position, which optimizes venous return )
A-E approach
positive pressure ventilation / Bambu bag( bag valve mask)
or biPAP
secure the airways -
intubate
Severe bronchospasm: Administer a bronchodilator.
SABA: e.g., albuterol nebulizer OR albuterol MDI
Consider a muscarinic antagonist additionally: e.g., ipratropium (off-label use
Fluid resuscitation
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intramuscular epinephrine shot
1:1000 concentration ( 1:1,000 solution into a vein leads to cardiac arrest)
0.01mg/kg !!
<6 years = 150mcg
6-12= 300mcg
>12 = 500mcg
adrenaline IV can only be given by trained specialists
repeat after 5 mins if no better
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aggressive IV colloid (normal saline) resuscitation - large bore IV access
20ml/kg
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chlorphenamine - IM or slow IV <6months - 250mcg/kg 6mo-6yr = 2.5mg <12 yr = 5mg >12 = 10mg
or
5 hydrocortisone - IM or slow IV 25mg 50mg 100mg 200mg
or
antihistamines
h1 - diphenhydramine
1 mg/kg IV/IM/PO every 6 hours
h2 - ranitidine - 1 mg/kg IV once as needed
what is the atopic triad ?
atopic dermatitis
asthma
allergic rhinitis
which runs in families
symptoms for
allergic rhinitis ,
sinusitis - usually with allergic rhinitis
conjunctivitis ,
hay fever symptoms
rhinorrhea , nasal congestion postnasal drip
Itchy nose
allergic rhinitis commonly mistreated in children as recurrent sore throat and URTI
sneezing,
itchy throat
chronic cough is common in allergic rhinitis or sinusitis due to POSTNASAL DRIP
Cobblestone appearance of the posterior pharyngeal wall
hypertrophic turbinates
Nasal polyps seen in 25–30% with chronic allergic rhinitis.
Allergic shiners: hyperpigmentation and edema of the lower eyelid as a result of venous congestion
typical of pollen and contact through mucus membrane
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redness
itching eyes
