Urticaria (DERM) Flashcards
Define urticaria.
Erythematous, blanching, oedematous, non-painful, pruritic lesions that develop rapidly, usually over minutes
How long does urticaria typically last?
<24 hours and leaves no residual skin markings upon resolution
What are some episodes of urticaria associated with?
Approximately 40% of episodes have associated angio-oedema (sudden, pronounced swelling of the subdermis/mucous membranes, may be painful rather than itchy + lasts up to 72h)
What is the difference between acute and chronic urticaria?
- acute - occur over a period of <6 weeks, usually caused by a specific stimulus, self-limiting
- chronic - occur over a period >6 weeks and are rarely attributable to a specific stimulus
What is the aetiology of urticaria?
- caused by activation of mast cells in the skin –> release of histamines
- cytokine release –> capillary leakage –> skin swelling and vasodilation –> erythematous appearance
What is acute urticaria triggered by? (3)
- mainly allergy related (food and drugs) = IgE mediated; direct mast cell degranulation
- insect bites, contact with allergens
- viral infections (non-IgE mediated mechanisms)
What is chronic urticaria triggered by? (7 + 1)
- heat
- cold
- pressure
- sunlight
- vibration
- ACh release
- water
Autoimmune/antibody associated in nature –> presence of IgG antibodies to high-affinity IgE receptor OR to IgE –> mast cell activation
What conditions can trigger chronic urticaria? (2)
- Hashimoto’s thyroiditis
- SLE
What are drug causes of urticaria? (4)
- aspirin
- penicillins
- NSAIDs
- opiates
What could make angio-oedema serious?
Involves face/neck - can compromise airway, requires prompt management
What are the clinical features of urticaria? (5)
- erythematous oedematous lesions - pale, pink, smooth raised skin (wheals)
- pruritus
- resolution within 24h
- swelling of face, tongue or lips (40% of urticaria cases associated with angioedema)
- blanching lesions (on palpation)
What are the risk factors for urticaria? (5)
- family Hx
- exposure to drug trigger
- exposure to food trigger
- recent insect bite or sting
- recent viral infection
What are the first-line investigations for urticaria? (3)
- FBC with differential
- CRP/ESR - normal or raised
- C4 level - decreased in hereditary and acquired angioedema
What does FBC with differential show in urticaria?
- eosinophilia: drug-induced
- neutrophilia: urticarial vasculitis
When do we do CRP/ESR for urticaria?
If urticarial vasculitis suspected
What special tests could we do for urticaria? (2)
- skin prick testing
- allergen avoidance diet - see if it improves
What are some differential diagnoses for urticaria? (9)
- anaphylaxis - respiratory symptoms (wheeze), hypotension, N/V, diarrhoea, IM epi
- dermatographism
- atopic dermatitis
- urticarial vasculitis - painful, >24h, residual marks upon resolution, found on biopsy, elevated ESR/CRP
- urticarial pigmentosa - small macules/raised papules vs large wheals, Darier’s sign (urticaria on rub/scratch/stroke)
- systemic mastocytosis
- carcinoid - cutaneous flushing
- contact dermatitis - more confluent and irritated
- papular urticaria (insect bites) - smaller papules >24h
How is urticaria diagnosed?
Clinical diagnosis based on history and exam
What is key to managing urticaria prophylaxis?
Trigger identification and avoidance
What is the 1st-line treatment for acute urticaria?
Antihistamines (e.g. loratadine, cetirizine)
How do we manage urticaria that is severe or recurrent?
Systemic corticosteroid (prednisolone)
How do we manage acute urticaria with airway involvement?
Adrenaline + airway protection + IV antihistamine (diphenhydramine)
How do we manage chronic urticaria?
- treatment of underlying illnesses
- antihistamine
- consider H2 antagonist
- consider systemic corticosteroid
- consider LTRA
- 2nd line: omalizumab
- 3rd line: ciclosporin
How do we manage hereditary angioedema?
- C1 esterase inhibitor or ecallantide or icatibant
- 2nd line: FFP
What are some complications of urticaria? (3)
- excoriations
- sedation (antihistamine side effect)
- skin infections
What is the prognosis like for urticaria?
Excellent - vast majority of patients response well to therapy with non-sedating antihistamines, and the condition is short-lived
