urticaria Flashcards
definition of urticaria
skin condition characterised by erythematous blanching, oedematous, non-painful, pruritic lesions
develop rapidly over minutes
typically resolve in 24hrs and leave no residual markings
what is acute urticaria
lasts <6wks
due to hypersensitivity reaction to a specific trigger
unerlying viral infections are common cause - particularly in children
usually self-limiting
what is chronic urticaria
characterised by daily, or nearly daily episodes of hives occuring for 6wks or more
complex aetiology
what is angiooedema
swelling involving deeper layers of the subdermis and mucous membranes
occurs in association with urticaria in about 40% cases
can happen in abscence of urticaria
mainly affecys face, lips, mouth, upper airway, genitals and extremities
when happens in face or neck - can comprimise airway
painful rather than itchy
lasts up to 72hours
epidemiology of urticaria
lifetime prevalence for acute is approx 20%
30% people with acute go onto develop long term symptoms
acute - more common in children, and adolescents
chronic - adults
chronic - women more
aetiology of acute urticaria
many causes are allergic - caused by IgE mediated reaction
food - milk, eggs, peanuts, tree nuts, finfish, shellfish
insect bites/stings or contact with other allergens eg animal dander
drugs - beta-lactam AB through IgE mediated allergic reaction
drugs eg NSAIDs, aspirin, opioids, vancomycin via direct mast cell degranulation
viral infections and radiocontrast dye trigger acute urticaria through non-IgE-mediated mechanisms
aetiology of chronic urticaria
chronic inducble urticaria may be triggered by heat, cold, pressure, sunlight, vibration, ACh release and water
have spontaneous, unpredictable lesions - half thought to be autoimmune/Ab associated in nature owing to IgG Ab to high affinity IgE receptor, or to IgE which are able to activate mast cells
minority of chronic spontaneous urticaria cases occur in association with autoimmune disease eg Hashimoto’s thyroiditis or SLE
can occur as a manifestation of unusual conditions, such as exercise-induced anaphylaxis, urticaria pigmentosa, or systemic mastocytosis.
pathology or urticaria
release of bioactive mediators from mast cells and basophils, after activation of either innate or adaptive immune system
mast cells are distributed through the body inc the dermis, subdermis and mucosal surfaces
when mast cells are activated - degranulation leads to rapid release of preformed vasoactive mediators inc histamine, leukotriene C4 and prostaglandin D2
this leads to vasodilation, increased vascular permeability and sensory nerve activation = oedema and pruritis
second delayed release of inflam cytokines (TNF, IL-4, IL-5( account for inflam infiltrate and longer-lasting lesions
biopsy of skin shows dense peri-vascular inflammatory infiltrate consisting of CD4+ lymphocytes, eosinophils, basophils and neutrophils
what is inducible urticaria
was known as physical urticaria
Sub-types include dermatographism, cholinergic, delayed pressure, sunlight (solar), cold, vibratory, and water (aquagenic).
RF for urticaria
FH
exposure to drug/food trigger
recent viral infection (non-IgE)
recent insect bite or sting
drug triggers
antibiotics (e.g., penicillins and cephalosporins),
cardiovascular drugs (e.g., amiodarone, procainamide),
immunotherapeutics and vaccines,
cytostatic agents (e.g., bleomycin, cisplatin, fluorouracil),
ACE inhibitors,
calcium-channel blockers,
drugs that can cause non-specific histamine release (e.g., non-steroidal anti-inflammatory drugs, narcotics, succinylcholine, amfetamine, hydralazine, and radiographic contrast media).
sx of urticaria
erythematous oedematous lesions - distributed on any part of the body
blanching lesions
pruritis
resolution within 24hr
swelling of the face, tongue or lips when associated with angiooedema
urticaria Ix
FBC with differential - may be normal, eosinophil (drug induced rns) or neutrophil count (associated with urticarial vasculitis) may be elevated
ESR in initial tests for chronic and in acute if urticarial vasculitis is suspected - elevated or normal
CRP - elevated or normal
