reactions Flashcards
what mediates type 1 hypersensitivity reactions?
IgE -> mast cell degranulation -> histamine release
what are features of type 1 hypersensitivity?
urticaria (hives) - pruritic, raised wheals, dermal oedema
angioedema - subcutaneous tissue/mucous membrane swelling
anaphylaxis - pharyngeal oedema, bronchospasm, hypotension, tachycardia
how quickly does a type 1 hypersensitivity reaction happen?
immediate
what investigations are used for type 1 hypersensitivity reactions?
specific IgE, skin-prick testing, serum mast cell tryptase level
what is the management of type 1 hypersensitivity reaction?
antihistamines
steroids
adrenaline (anaphylaxis)
what is type 4 hypersensitivity reaction mediated by?
T cells
antigen specific
how long does it take a type 4 hypersensitivity reaction to occur?
delayed - days
what are some features of type 4 hypersensitivity reaction?
maculopapular drug eruption
erythema nodosum
erythema multiforme
phototoxic drug reactions
how does maculopapular drug eruption present?
widespread symmetrical red maculopapular rash
itchy
mild efevl
what is the onset of maculopapular drug eruption?
4-21 days after taking the drug
what is seen in severe maculopapular drug eruption?
mucous membrane involved
blistering
facial oedema
what is erythema nodosum?
panniculitis (subcut fat inflammation)
who does erythema nodosum typically present?
females 25-40 years old
how does erythema nodosum clinically present?
tender dusky blue-red warm nodules on anterior shin
what is erythema nodosum a result of hypersensitivity due to?
infection - strep, sarcoidosis
drugs - sulphonamides, oral contraception
what is the management of erythema nodosum?
treat underlying cause + NSAIDs
how does erythema multiforme clinically present?
target lesion - dark/dusky central area with surrounding red rings
what is acute onset erythema multiforme due to?
infection - HSV, mycoplasma pneumoniae (children)
drugs - sulphonamides, NSAIDs, phenytoin
what are some other presentations of type 4 hypersensitivity reactions?
fixed drug eruption - red, round painful plaques in same area every time
acneiform - glucocorticoids
drug-induced bullous penphigoid - ACE inhibitors
what are some severe type 4 hypersensitivity reactions?
Stevens-Johnson syndrome (SJS)
toxic epidermal necrolysis
DRESS
what is SJS?
epidermis necrosis
what will be seen in SJS?
Nikolysky sign positive
mucosal lesions
starts of face/chest
what is toxic epidermal necrolysis?
widespread subepidermal blistering
what is seen in DRESS?
mucocutaneous rash
fever
lymphadenopathy
what drugs are used to treat DRESS?
aromatic anticonvulsants (carbanazepine)
what are the signs of phototoxic drug reactions?
erythema, prickling, pigmentation
inc. skin fragility
