This is a potentially lethal condition. Angioedema manifests with rapid development of oedematous swelling of the lip(s), tongue and oral or facial swelling (Fig. 32.1). This can be life-threatening as oedema may also involve the neck and hazard the airway. The swelling in angioedema is usually relatively transient and the skin does not scale.
Angioedema is usually allergic (a type 1 hypersensitivity response seen mainly in those with an atopic tendency) but can rarely be drug-induced, hereditary (hereditary angio-neurotic oedema or HANE; caused by a deficiency of the complement component C1 esterase inhibitor – C1-INH) or C1-INH deficiency can be acquired.
It is IgE mediated and causes mast cell activation and degranulation, with release of histamine and bradykinin, causing vasodilatation and increased vascular permeability. The C4 complement component is consumed and thus plasma levels fall, but the levels of C1 and C3 are usually normal.
The acute oedema, which appears < 2 h of antigen exposure, can cause pronounced itchy labial and periorbital swelling, and can involve any oral site, but when oedema involves the tongue and neck and extends to the larynx, it can cause rapidly fatal respiratory obstruction.
Angioedema is diagnosed clinically and from a history of atopic disease and/or exposure to allergen, and sometimes by allergy testing (prick test), but only where there are appropriate resuscitation facilities and an emergency kit containing injectable adrenaline at hand. Mast cell tryptase levels may be raised. Hereditary angioedema (HANE) may need to be excluded – HANE has low C4, but normal C3 levels, and absence of C1-INH activity (Table 32.1).
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