(Hereditary Angioedema, HAE)

HAE causes recurrent episodes of angioedema in the upper respiratory, gastrointestinal tract or in subcutaneous tissues.

Acute episodes of angioedema may be triggered by infection, stress, menstruation, surgery, dental work, trauma and some medicines (including oestrogen-containing contraceptives and ACE-inhibitors) or may have no clear trigger.

HAE is a rare autosomal dominant condition in which C1 esterase inhibitor levels are reduced (HAE type I) or poorly functional (HAE type II). HAE is diagnosed by the finding of low C1 esterase inhibitor level or function. C4 level is also low during episodes of angioedema.

Assessment

Clinical features include:

• Angioedema without pruritis and without urticaria (hives) 
• Abdominal pain (+/- nausea/vomiting) due to intestinal oedema
• Laryngeal oedema

Angioedema episodes usually take several hours to develop, and if untreated last 1-5 days.

Mild/moderate angioedema episodes

Present with:

• Swelling of the peripheries
• Mild/moderate abdominal pain

Severe angioedema episodes

Present with:

• Stridor or respiratory distress due to laryngeal oedema
• Other signs of potential airway compromise eg hoarse voice, persistent cough, dysphagia or tongue swelling 
• Severe abdominal pain or vomiting

Management

Mild/moderate angioedema episodes

Treatment is conservative:

• Hospital admission is not usually required
• Other causes of abdominal pain may need to be excluded, and abdominal ultrasound may help by showing intestinal wall oedema or ascites in HAE-related angioedema.
• A 3 day course of tranexamic acid may be considered to shorten the duration of symptoms (12-25 mg/kg/dose (max 1.5 gm) 3-4 times per day)

Severe angioedema episodes

Severe angioedema episodes can be fatal. Management includes:

• Hospital admission for all severe angioedema episodes
• If upper airway obstruction is present, notify a senior staff member experienced in endotracheal intubation
• Intravenous C1 esterase inhibitor concentrate should be administered (see below for dosing)
• Notify the on-call Allergy/Immunology Consultant in all cases

Planned surgery or Oropharyngeal procedures

Surgery or any traumatic procedure of the oropharyngeal area such as dental work should be carefully planned. The use of a prophylactic agent prior to such procedures reduces the risk of precipitating angioedema.

• Consult with an Immunologist and ICU before the procedure
• For planned procedures, danazol is the first choice of prophylactic agent, (10 mg/kg/day for 5-10 days before and 2-5 days after the procedure).
• For emergency or high-risk procedures, C1 esterase inhibitor concentrate (25 units/kg infusion given 1 hour prior to the procedure) - see Notes below
• Due to the risk of precipitating laryngeal oedema, oropharyngeal procedures should usually involve general anaesthesia with endotracheal intubation

Notes

Antihistamines and corticosteroids

Antihistamines and corticosteroids have no role in the management of HAE related angioedema. The role of adrenaline in the treatment of HAE is not well established. There are anecdotal reports of efficacy using nebulised or intramuscular adrenaline to treat upper airway angioedema, however C1 esterase inhibitor is the treatment of choice for airway angioedema caused by HAE.

C1 Esterase inhibitor concentrate (Berinert)

This is not TGA approved, and approval is required to use it on an individual patient basis. Consultation with the on-call immunologist is important. 25 units/kg (rounded to nearest 500 units) is infused over 1-2 minutes. 70% of angioedema episodes respond within 30 minutes of infusion, and 95% within 4 hours. If there is no response within 4 hours alternative diagnoses should be considered, but the dose may be repeated at this stage after further discussion with the on-call immunologist.