Superficial swelling of the skin that results in a red, raised, itchy rash. It can be localised or generalised.
Pathophysiology
- Release of a variety of inflammatory mediators (including histamine, bradykinin, leukotrienes, prostaglandins) cause close-by vessels to become leaky. Leakage of plasma causes the classic oedema/wheal whilst histamine causes an itch.
- Can either be immune mediated on ‘non-immune’ urticaria
- Immune-mediated urticaria
- Can be associated with a type I (immediate allergic IgE-mast cell response e.g. to latex, cosmetics); type II (cytotoxic T cell mediated causing an urticarial vasculitis (e.g. hereditary angioedema) and type III (immune-complex diseases e.g. SLE that can cause urticaria).
- Non-immune mediated
- Normally complement mediated in viral/bacterial infections but can also be due to transfusion reactions (technically IgE mediated), opioids and other drugs, physical stimulation etc
- Note Idiopathic urticaria and chronic urticaria
- Some patients exhibit chronic urticaria for which there is no known cause/pathogenesis. About a 1/3 of chronic cases are thought to be immune mediated.
- Immune-mediated urticaria
Presentation
- Classic urticarial weals (small, raised areas 1-2cm that develop suddenly and usually last <24 hours, but may reappear again within hours) with itch
- Acute <6weeks vs Chronic >6weeks
- It is important to ask about:
- the possibility of food allergy (new food/prev allergy)
- drug history (particularly NSAIDs/aspirin, OTC medications, supplements, penicillins, ACE inhibitors) as there may be an allergy. Note also any PMHx.
- Any recent viral/bacterial infections (acute or chronic)?
- Where the hives caused by physical stimuli (hot/cold/pressure etc)?
- Any bites/insect manifestations?
- Also take an extensive occupational/hobbies history.
Investigations
- You might (based on the history) want to do FBC/U&E/LFTs and or blood cultures if you suspect a more systemic cause (e.g. urticarial vasculitis where urticaria is painful and persistent).
- You might also want to do RAST if there is a specific allergen that you think could be causing the urticaria.
Management
- Where possible, avoid the trigger
- For severe acute urticaria, consider using a short course of prednisolone (40mg/day 3-5 days) in addition to a non-sedating anti-histamine e.g. (cetirizine, fexofenadine, loratidine)
- Antihistamines are the main treatment otherwise (other than treatment of the underlying cause)
- sedating anti-histamines may be useful for patients who have problems with nocturnal itching (not uncommon)
- cooling agents e.g. menthol/calamine may also be of benefit
- consider referral to a specialist if symptoms persist >6 weeks and are not responding to treatments
Notes on Medicine/Surgery 