Hereditary angioedema

Hereditary angioedema (HAE) is an autosomal dominant condition associated with low plasma levels of the C1 inhibitor (C1-INH, C1 esterase inhibitor) protein. C1-INH is a multifunctional serine protease inhibitor - the probable mechanism behind attacks is uncontrolled release of bradykinin resulting in oedema of tissues.

Investigation

• C1-INH level is low during an attack
• low C2 and C4 levels are seen, even between attacks. Serum C4 is the most reliable and widely used screening tool

Symptoms

• attacks may be proceeded by painful macular rash
• painless, non-pruritic swelling of subcutaneous/submucosal tissues
• may affect upper airways, skin or abdominal organs (can occasionally present as abdominal pain due to visceral oedema)
• urticaria is not usually a feature

Management

• acute
  • HAE does not respond to adrenaline, antihistamines, or glucocorticoids
  • IV C1-inhibitor concentrate, fresh frozen plasma (FFP) if this is not available
  • Icatibant: a selective bradykinin B2 receptor antagonist ⇒ SC 30mg 1 dose, then 30mg after 6h if required (max. 3 doses per day)
• prophylaxis:
  • anabolic steroid Danazol may help