Hereditary angioedema and acquired angioedema are caused by deficiency or dysfunction of C1 inhibitor, a protein that regulates the classical complement activation pathway (see Biology of the Immune System: Complement System). Diagnosis is by measurement of complement levels. C1 inhibitor is used to treat acute attacks. Prophylaxis is with attenuated androgens, which increase C1 inhibitor levels.

C1 inhibitor deficiency or dysfunction results in increased levels of bradykinin because C1 inhibitor also inhibits activated factor X11a and activated kallikrein, which are required for the generation of bradykinin, in the kinin system pathway.

Hereditary angioedema: Hereditary angioedema has 2 types:

• Type 1 (85%): Characterized by C1 inhibitor deficiency
• Type 2 (15%): Characterized by C1 inhibitor dysfunction

Inheritance is autosomal dominant. Clinical presentation is usually during childhood or adolescence.

Acquired C1 inhibitor deficiency : C1 inhibitor deficiency may be acquired when

• Complement is consumed in neoplastic disorders (eg, B-cell lymphoma) or immune complex disorders.
• C1 inhibitor autoantibody is produced in monoclonal gammopathy.
• Rarely, C1 inhibitor autoantibody is produced in autoimmune disorders (eg, SLE, dermatomyositis).

Clinical presentation is usually at an older age, when patients have an associated disorder.

Triggers: In all forms of hereditary and acquired angioedema, attacks can be precipitated by mild trauma (eg, dental work, tongue piercing), viral illness, cold exposure, pregnancy, or ingestion of certain foods or may be aggravated by emotional stress.

Symptoms and Signs

Symptoms and signs are similar to those of other forms of bradykinin-mediated angioedema, with asymmetric and mildly painful swelling that often involves the face, lips, and/or tongue. Swelling may also occur on the back of hands or feet or on the genitals. The GI tract is often involved, with manifestations that suggest intestinal obstruction, including nausea, vomiting, and colicky discomfort. Pruritus, urticaria, and bronchospasm do not occur, but laryngeal edema may be present, causing stridor (and sometimes death).

Swelling resolves within about 1 to 3 days of onset. In hereditary angioedema, symptoms resolve as complement components are consumed.

Diagnosis

• Measurement of complement levels

Levels of C4, C1 inhibitor, and C1q (a component of C1) are measured. Low levels of C4 (and C2, if measured) and decreased C1 inhibitor function confirm hereditary angioedema or acquired C1 inhibitor deficiency. Other findings include

• Type 1 hereditary angioedema: Low C1 inhibitor levels and normal levels of C1q
• Type 2 hereditary angioedema: Normal or increased C1 inhibitor levels and normal C1q levels
• Acquired C1 inhibitor deficiency: Low C1q levels

If angioedema is not accompanied by urticaria and recurs without any clear cause or is present in family members, clinicians should suspect hereditary angioedema or acquired C1 inhibitor deficiency.

Treatment

• For acute attacks, C1 inhibitor, ecallantide, or icatibant
• For prophylaxis, attenuated androgens

Acute attacks are treated with purified human C1 inhibitor, ecallantide, or icatibant (not available in the US). If none of these drugs is available, fresh frozen plasma or, in the European Union, tranexamic acidSome Trade Names
CYKLOKAPRON
Click for Drug Monograph
has been used. A recombinant form of C1 inhibitor is being developed. EpinephrineSome Trade Names
ADRENALIN
PRIMATENE MIST
Click for Drug Monograph
can provide transient benefit in acute attacks when airways are involved. Corticosteroids and antihistamines are not effective. Analgesics, antiemetics, and fluid replacement can be used to relieve symptoms.

Pearls & Pitfalls Antihistamines and corticosteroids are not effective for hereditary angioedema.

For long-term prophylaxis, attenuated androgens (eg, stanozololSome Trade Names
WINSTROL

2 mg po tid, danazolSome Trade Names
DANOCRINE
Click for Drug Monograph
200 mg po tid) are used to stimulate hepatic C1 inhibitor synthesis. This treatment may be less effective for the acquired form. C1 inhibitor is effective but expensive.

Short-term prophylaxis is indicated before high-risk procedures (eg, dental or airway procedures) if C1 inhibitor is not available to treat an acute attack. Patients are usually given attenuated androgens 5 days before the procedure until 2 days afterward. If C1 inhibitor is available, some experts advocate giving it 1 h before high-risk procedures rather then attenuated androgens for short-term prophylaxis.

Key Points

• Onset is usually during childhood or adolescence (hereditary) or during later adulthood (acquired), often in patients with a neoplastic or an autoimmune disorder.
• Mild trauma, viral illness, cold exposure, pregnancy, or ingestion of certain foods may trigger attacks; emotional stress may aggravate them.
• Measure complement levels; low levels of C4 and decreased C1 inhibitor function indicate hereditary angioedema or acquired C1 inhibitor deficiency.
• For acute attacks, use purified human C1 inhibitor, ecallantide, or icatibant, and for symptom relief, use analgesics, antiemetics, and fluids; antihistamines and corticosteroids are ineffective.
• For prophylaxis (long-term and short-term—eg, before dental or airway procedures), use attenuated androgens (eg, stanozololSome Trade Names
  WINSTROL
  
  , danazolSome Trade Names
  DANOCRINE
  Click for Drug Monograph
  ).

Last full review/revision July 2012 by Peter J. Delves, PhD

Content last modified November 2012