Hypersensitivity Disorders B&B Flashcards
what changes occur to the epidermis in urticaria?
aka hives, allergic skin reaction
NONE! urticaria is dermal edema - dilation of lymph vessels
Type I hypersensitivity caused by mast cell degranulation —> histamine release
which immune components mediate atopic dermatitis?
aka eczema - mediated by T cells and cytokines, 80%+ have increased IgE levels
usually occurs in children (most have family history), chronic disorder with flares/remission of red/pruritic rash
where does atopic dermatitis present in babies vs adults?
aka eczema - mediated by T cells and cytokines, 80%+ have increased IgE levels
babies - face (cheeks), scalp
children/adults - lichenified (thickened) plaques on flexures (antecubital and popliteal fossa)
when do drug rashes present, and what type of hypersensitivity reaction is this?
days to weeks after starting drug, Type IV (T-cell mediated, delayed) hypersensitivity
maculopapular, may be pruritic (or not), no fever/wheezing/joint pain
what type of antibiotic is often associated with drug rash?
penicillin antibiotics
days to weeks after starting drug, Type IV (T-cell mediated, delayed) hypersensitivity
Stevens-Johnson Syndrome
severe skin reaction (Type IV hypersensitivity, T cell mediated) usually triggered by drugs —> causes epidermal necrosis (risk of dehydration + infections - high morality risk)
will present with Nikolsky sign: skin slips off with gentle tug
if >30% skin surface area is affected, it is called toxic epidermal necrolysis
3 conditions that present with Nikolsky sign
[skin slips off with gentle tug]
- Stevens-Johnson Syndrome: severe skin reaction to drug (epidermal necrosis)
- Staph. aureus scalded skin syndrome (child)
- Pemphigus vulgaris: Abs against desmosomes
Pt presents to their physician with concern of a rash spreading across their face and chest. They are recovering from a febrile illness 3 days prior. The rash appears to be spreading symmetrically, and the skin is red and tender. Mucosal membranes are affected, as well. In some areas, the skin is sloughing off. What is the diagnosis, and what complication are you concerned about?
Stevens-Johnson Syndrome: severe skin reaction (Type IV hypersensitivity, T cell mediated) usually triggered by drugs —> causes epidermal necrosis
will present with Nikolsky sign: skin slips off with gentle tug
complications include dehydration and risk of infection from loss of skin barrier
what are 2 infectious and 3 drug-related causes of erythema multiforme?
90% of cases associated with infection:
1. herpes simplex virus
2. mycoplasma pneumoniae (children)
drugs:
1. sulfa drugs
2. NSAIDs
3. phenytoin
[also some cancers and autoimmune diseases]
what is the hallmark clinical finding of erythema multiforme?
multiple lesion types present, but hallmark is ”target lesion”: dark/dusty central area surrounded by red rings (patchy shape)
symmetrical distribution, starts on back of hands and feet and spreads inwards
90% of cases associated with infection, most often HSV
