This document discusses anaphylaxis and urticaria. It defines urticaria and angiodema, describes the pathophysiology involving mast cell release of vasoactive substances, and classifies different types including chronic, acute, physical, contact, pharmacological and systemic causes. It notes that 75% of cases are chronic idiopathic or acute, while 20% are physical or related to cholinergic urticaria. Investigations are often unnecessary but can include tests to rule out other systemic illnesses or identify triggers. Emergency management involves epinephrine, antihistamines, and steroids. Long-term management focuses on avoiding triggers and using antihistamines.

1. Anaphylaxis

2. Definitions
Urticaria – Transient,
often pruritic lesions,
involving acute dermal
oedema.
.
Angiodema – As above
but larger, involving
dermis and sub-cutis

3. Pathophysiology
Mast-cell release of vasoactive substances
leading to inc. dilatation and permeability
– Type I hypersensitivity
– Complement activation
– Histamine release
– Antagonism of prostaglandin pathway
– ?Serum histamine releasing factor

4. Classification
• Chronic
• Acute
• Physical
• Contact
• Pharmacological
• Systemic Cause
• Inherited
• Other

5. • 75% chronic idiopathic/acute
• 20% - physical or related to cholinergic
urticaria

6. Chronic Idiopathic
• Wheals lasting >1 day, varying in size and
appearance
• May have angioedema
• May be drug related, often no cause identified

7. Acute Urticaria
• Sudden onset, +/- angioedema,
• History frequently identifies allergen, food,
drug or contact

8. Physical Urticarias
• Cold, heat, sun, pressure, sweating
• Dermographism, in 5% “normal” can be
exaggerated/symptomatic

9. Hereditary angioedema
• Rare, autosomal dominant condition
• Often presents in childhood with angioedema
of larynx and GIT
• Deficient C1 esterase inhibitor leads to excess
complement activation and ++ vasoactive
substances
• Treat
– acutely, IV c1 esterase inhibitor
– Steroids – induce liver enzyme synthesis

10. Urticarial Vasculitis
• Often acute onset urticaria
• Lesions last over 24hrs, leaving purpuric rash

11. Investigations
• Often unnecessary
• FBC, LFT, ANA + urinanalysis, to exclude
systemic illness
• Dermography – firmly stroke skin
• Cold urticaria – Ice cube test
• ? Hereditary angioedema – c1 esterase
inhibitor level

12. Emergency management
• Acute airway/anaphylactic shock
– Adrenaline IM, 0.5-1mg (rpt after 5 mins if req)
– Antihistamine IV infusion
• Ie chlorpheniramine, 10-20mg slow infusion
– IV steroids (delayed onset, useful after several
hours)

13. Management
• Avoid precipitant factors/exposure therapy
• Antihistamines, reduce wheal size/itch
• Corticosteroids, occasionally used in severe,
acute situations (not chronic)