Urticaria Flashcards
Define Urticaria
Erythematous, blanching, oedematous, non-painful, pruritic lesions that develop rapidly, usually over minutes.
Typically lasts <24h and leaves no residual skin marking upon resolution.
“wheal and flare”
Aetiology of acute Urticaria
<6 weeks
Allergic reaction (due to IgE-mediated reaction)
Foods: milk, eggs, peanuts, tree nuts, finfish, shellfish
Insect bites/stings or contact with allergens
Drugs: beta-lactams, NSAIDs, aspirin, opioids, vancomycins
Viral infections
Radiocontrast dye trigger acute urticaria
Aetiology of chronic Urticaria
Mainly spontaneous, unpredictable lesions
<10% have inducible urticaria
Triggers: heat, cold, pressure, sunlight, vibration, acetylcholine release, and water
May occur in association with autoimmune disease e.g. Hashimoto’s thyroiditis or SLE
Symptoms of Urticaria
Erythematous oedematous lesions (Sudden onset | No overlying flaking or scaling
Pruritus
Resolution within 24 hours
Swelling of face, tongue, or lips (angioedema)
What is the difference between acute and chronic urticaria
Acute Sudden onset, isolated lesions lasting < 24 hours - Typically few hours at a time Total duration of flares 6 weeks or less Intermittent episodes Self-limiting
Chronic Recurrent whealing of skin at least twice weekly for more than 6 weeks Single lesion still last < 24 hours More common in women Most cases are idiopathic
Signs of urticaria
Erythematous oedematous lesions
Swelling of face, tongue, or lips
Blanching lesions
Stridor (laryngeal angio-oedema)
Investigations for urticaria
Not necessary if clearly identifiable food or medication precipitant
For lesions lasting >24 hours, atypical lesions, or if accompanying fever → skin biopsy to confirm urticaria vs DDx
FBC: normal or eosinophilia/neutrophilia
ESR/CRP: elevated or normal
C4 level: low in hereditary and acquired angio-oedema
ANA: rheumatological disease
