Definitions
Urticaria
- Superficial swelling (epidermis/mucous membranes)
- Red, raised, intensely itchy rash with pale center
Angioedema
- Deeper swelling (dermal, subcutaneous, submucosal)
- Commonly affects face (lips, tongue, eyelids), genitalia, hands, feet
- Often occurs with urticaria but may be isolated
Clinical Features
- Common sites: Face, genitalia, hands, feet
- Bowel involvement:
- Abdominal pain, nausea/vomiting
- Distension, diarrhea/constipation
- Airway involvement:
- Stridor → potential complete obstruction
- Medical emergency
Classification
Acute Allergic Angioedema (90%)
- IgE-mediated mast cell degranulation
- Usually with urticaria within 1-2h of allergen exposure
- Self-limiting (1-3 days) but relapses common
Non-Allergic (Bradykinin-Mediated)
- Drug-induced:
- ACE inhibitors most common
- Days-months after starting drug
- May persist months after stopping
- Hereditary Angioedema (HAE):
- Autosomal dominant C1-esterase inhibitor deficiency
- Presents post-puberty with recurrent episodes
- GI symptoms may mimic acute abdomen
- Acquired Angioedema (AAE):
- Secondary to lymphoma or connective tissue disorders
- Similar presentation to HAE
Idiopathic Angioedema
- Chronic, relapsing with unknown cause
- Associated with autoimmune disorders (SLE, thyroiditis)
Diagnosis
With Urticaria
- Allergic: Transient, within 1-2h of known allergen
- Idiopathic: Recurrent with no identifiable cause
Without Urticaria
- Drug reaction: ACE inhibitor use
- HAE: Family history
- AAE: Known lymphoma/connective tissue disorder
Differential Diagnosis
- Evolving anaphylaxis
- Cellulitis/erysipelas
- Lymphoedema
- SLE
- Contact dermatitis
Emergency Department Management
Initial Assessment
- ABC approach - assess for life-threatening conditions
- If anaphylaxis suspected → treat as anaphylaxis
Allergic Angioedema
- Rapidly developing (non-anaphylactic):
- IV/IM chlorphenamine + hydrocortisone
- Emergency admission
- Stable cases:
- Identify/avoid triggers
- Mild cases may not need treatment
- Symptomatic treatment:
- Non-sedating antihistamine (cetirizine/fexofenadine/loratadine) for ≤6 weeks
- Severe cases: Add prednisolone 40mg daily ≤7 days
- Advise emergency care if symptoms progress
Hereditary Angioedema (HAE)
- Key points:
- Bradykinin-mediated → resistant to adrenaline/antihistamines/steroids
- Requires specific treatment
- Treatment options:
- Icatibant (bradykinin B2 receptor antagonist) - SC injection
- C1 esterase inhibitor concentrate (IV)
- Fresh frozen plasma (2 units IV)
Clinical Comparison
| Feature |
Allergic |
Non-Allergic |
Anaphylaxis |
| Onset |
Acute |
Gradual |
Rapid |
| Skin |
Urticaria + pruritus |
No pruritus |
Variable |
| Systemic |
Localized, normotensive |
Localized, normotensive |
Respiratory/cardiovascular collapse |
| Other |
- |
Abdominal pain, previous episodes |
Progressive symptoms |
Key Clinical Pearls
- ACE inhibitors are the most common cause of drug-induced angioedema
- HAE often presents with recurrent abdominal pain episodes
- Airway involvement requires immediate intervention
- Bradykinin-mediated angioedema won't respond to standard allergy treatments