allergy and hypersenitivity Flashcards
what is the clinical presentation of allergic reactions?
severe symptoms include
urticaria
angioedema
anaphylaxis
how quickly does an allergic reaction happen ?
usually occurs within a few minutes of exposure to the antigen but can be occasionally delayed
how do you approach an allergic reaction ?
establish the time lag between the exposure to the antigen and onset of symptoms drug intake allergens at home family history occupation
what is urticaria ?
urticaria is characterized by mucosal swelling due to plasma leakage
what is the difference between urticaria and angioedema ?
urticaria is superficial dermal swelling, which is often pruritic and is pink or pale in the centre
angioedema is deep dermal swelling, which is often painful and is not accompanied by any colour changes
what are the characteristics of urticaria ?
the hallmark of wheals is that individual lesions come and goo rapidly, by definition within 24 hours , all urticarias are initially acute
what is the main cause of urticaria ?
idiopathic
upper respiratory tract infection
what is a life threatening complication of angioedema ?
laryngeal edema causing airway compromise
what is the other name for hereditary angioedema ?
C1 esterase inhibitor deficiency
what is C1 esterase inhibitor deficiency characterized by?
recurrent episodes of angioedema without urticaria or pruritus
what are the investigations for allergic reactions ?
full CBC ( eosinophilia) Serum IgE skin prick test challenge test C1 esterase inhibitor deficiency
what is the treatment of allergic reactions ?
allergens avoidance antihistamines corticosteroids leukotrienes receptor agonists monoclonal antibodies desensitization
what is always the first line treatment in allergic reactions ?
anti histamine
anaphylaxis ?
life threatening emergency
usually requires priming ( pre exposure to the antigen)
antigen must be systematically absorbed
rapid onset
what are the clinical features of anaphylaxis ?
bronchospasm facial and laryngeal edema hypotension nausea and vomiting death can occur within minutes
what is the treatment of anaphylaxis ?
ABCDE approach make sure patient is lying flat with feet raised open the airways o2 establish a venous access give subcutaneous adrenaline 0.5mg IV hydrocortisone
what is the non emergency treatment of anaphylaxis ?
prevention
epipen
desensitization
SJS vs TEN
steven johnson syndrome and toxic epidermal necrolysis
what is the percentage of skin detachment in SJS ?
less than 10%
what is the percentage of skin detachment in TEN ?
more than 30%
what is the percentage of skin detachment in SJS-TEN overlap ?
10-30%
what is the pathogenesis of SJS-TEN ?
type 4 hypersensitivity
how would you confirm a diagnosis of SJS-TEN ?
skin biopsy
what are the DDX with SJS-TEN?
staphylococcal scalded skin syndrome
other bullous disease of the skin
what is the management and treatment of SJS-TEN ?
hospital admission stop the offending drug fluid replacement wound care eye+mouth care IV cyclosporine , predinsolone
what is erythema multiforme ?
a self limited but potentially recurring disease and has two types one major and the other minor
what is the clinical presentation of erythema multiforme ?
abrupt onset of papular target lesions
what are the two types of lesions in erythema multiforme ?
typical- with at least three different zones
atypical - with only two different zones with poorly defined birders
relation between EM and TEN ?
EM doesn’t carry the risk of becoming TEN
what is the most common form of cutaneous drug eruption ?
exanthematous eruption also called
morbilliform or maculopapular eruptions
what is the clinical picture of exanthematous eruptions?
erythema, macules and papules
prominent pruritus
what is the treatment of exanthematous eruptions ?
topical steroids
antihistamines
supportive treatment
what is the prognosis of exanthalmous drug eruption ?
good prognosis , clears within two weeks when offending drug is removed
how do we test for a specific allergen ?
RAST test
what are the precipitating factors for EM ?
HSV
