Emergency Medicine · Allergic and Immunologic Emergencies
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ACE inhibitors are the most common cause of drug-induced angioedema due to the accumulation of bradykinin.
Hereditary angioedema (HAE) is caused by a deficiency or dysfunction of C1 esterase inhibitor, leading to unregulated activation of the kallikrein-kinin system.
Patients with HAE typically present with recurrent episodes of subcutaneous or submucosal edema without associated urticaria or pruritus.
C4 levels are the best initial screening test for HAE: C4 is almost always low during attacks and is usually low between attacks as well.
Icatibant, a bradykinin B2 receptor antagonist, is one of the first-line on-demand treatments for HAE attacks, along with intravenous C1-INH concentrate (plasma-derived or recombinant) and oral sebetralstat, an oral plasma kallikrein inhibitor; ecallantide remains effective but is no longer listed among first-line options.
Epinephrine, antihistamines, and corticosteroids are ineffective for bradykinin-mediated angioedema but are first-line for histamine-mediated (allergic) angioedema.
Airway protection via early endotracheal intubation is the priority in patients presenting with laryngeal edema and respiratory distress.
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A 54-year-old male presents to the emergency department with progressive swelling of his lips, tongue, and uvula over the past 4 hours. He denies any history of food allergies, insect stings, or recent exposure to new medications, except for a blood pressure medication started 3 weeks ago. Physical examination reveals non-pitting edema of the face and oropharynx without urticaria or pruritus. His blood pressure is 130/80 mmHg and his oxygen saturation is 94% on room air. He is currently taking lisinopril, atorvastatin, and metformin.
What is the most likely mechanism of this patient's condition?
Bradykinin-mediated angioedema due to ACE inhibitor use
The patient's presentation of isolated angioedema without urticaria is classic for ACE inhibitor-induced angioedema, which is mediated by the accumulation of bradykinin rather than histamine.
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Etiology / Epidemiology
Triggered by ACE inhibitors or C1 esterase inhibitor deficiency. Affects deep dermis and submucosa.
Clinical Manifestations
Non-pruritic (often painful or tense), asymmetric swelling of face/lips/tongue. Non-pitting edema without urticaria.
Diagnosis
C4 level is the best initial screening test. Low levels suggest hereditary angioedema.
Treatment
Secure airway first. Epinephrine for allergic; Icatibant or C1-INH concentrate for hereditary.
Prognosis
Risk of asphyxiation from laryngeal edema. Mortality high if airway is not secured.
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Epidemiology & Etiology
Most common drug-induced cause is ACE inhibitors, which can present years after initiation. Hereditary angioedema (HAE) is an autosomal dominant disorder involving C1 esterase inhibitor deficiency or dysfunction. Non-histaminergic forms are often triggered by trauma, stress, or dental procedures.
Pertinent Anatomy
Involves the deep dermis, subcutaneous, and submucosal tissues. Laryngeal involvement is the most critical anatomical site due to rapid progression to airway obstruction.
Pathophysiology
Histaminergic angioedema is mediated by mast cell degranulation. Bradykinin-mediated angioedema (ACE-I or HAE) results from excessive bradykinin production, which increases vascular permeability. Unlike histamine-mediated forms, it is resistant to antihistamines and glucocorticoids.
Clinical Manifestations
Presents as non-pitting, non-pruritic, and often asymmetric swelling. Laryngeal edema is a life-threatening emergency requiring immediate intubation. Absence of urticaria strongly points toward a bradykinin-mediated etiology rather than an allergic reaction.
Diagnosis
Screening for HAE requires C4 levels; low levels are highly sensitive. Confirmatory testing involves C1 esterase inhibitor protein and functional activity levels. During acute attacks, C4 is almost universally low in HAE type 1 and type 2. In contrast, C4, C1-INH level, and C1-INH function are all normal in HAE with normal C1-INH (HAE-nC1-INH), which is diagnosed by family history, clinical course, and genetic testing.
Treatment
For ACE-I induced or HAE, epinephrine, antihistamines, and steroids are ineffective. For HAE attacks use Icatibant or C1-INH concentrate; in ACE-I induced angioedema these agents failed to show benefit in randomized trials, so management is drug discontinuation plus airway observation. Avoid ACE inhibitors for life in patients with drug-induced angioedema.
Prognosis
Primary mortality risk is asphyxiation. Patients with frequent or severe HAE attacks are offered long-term prophylaxis; first-line options are lanadelumab, berotralstat, or plasma-derived C1-INH, with attenuated androgens (danazol) now second-line.
Differential Diagnosis
Anaphylaxis: presence of urticaria and pruritus
Cellulitis: associated with warmth, erythema, and fever
Contact dermatitis: associated with intense pruritus and vesicles
Superior Vena Cava Syndrome: associated with venous engorgement and dyspnea
Hypothyroidism: associated with myxedema and systemic metabolic signs