Snapshot A 15-year-old boy is rushed to the emergency department by his mother due to increased difficulty with breathing. His mother says that he does not have a food allergy and that this has happened to him before after undergoing a dental procedure. She reports that in the father's side of the family, they suffer from these episodes of swelling but usually self resolve. On physical exam, the patient has swelling of the lips, tongue, and skin around the face and arms. He is immediately sedated and subsequently intubated and treated for anaphylaxis which does not improve his symptoms. Laboratory testing is significant for decreased C4 and C1 inhibitor levels as well as normal C1q levels. Introduction Clinical definition hereditary C1 inhibitor deficiency that leads to recurrent angioedema without urticaria or pruritus triggers include physical dental work surgery intubation medical angiotensin-converting enzyme (ACE) inhibitors tamoxifen estrogen-containing medications (e.g., hormone replacement therapy and oral contraceptives) Genetics inheritance pattern autosomal dominant Associated conditions possibly associated with an increased incidence of autoimmune disease Prognosis variable after the attack occurs, they may recur throughout the patient's life attack frequency can be reduced with appropriate therapy Epidemiology Incidence 0.001%-0.003% of the general population Demographics typically begins in childhood and worsens during puberty Location skin, upper airway, and gastrointestinal tract Risk factors family history ETIOLOGY Pathophysiology pathobiology C1 inhibitor deficiency (hereditary angioedema type I) or dysfunction (hereditary angioedema type II) results in unchecked bradykinin production C1 inhibitor inhibits kallikrein and active factor XII, which is involved in the cleavage of high molecular weight kininogen into bradykinin decreased serum C4 levels due to increased C1 complex cleavage of C4 in the absence or dysfunction of C1 inhibitor Presentation Symptoms prodromal symptoms fatigue nausea and/or other gastrointestinal symptoms flu-like symptoms angioedema without urticaria or pruritus affecting the skin swelling of the extremities, face, and genitals can affect any area upper airway swelling of the lips, tongue, uvula, soft palate, and larynx gastrointestinal bowel wall edema resulting in gastrointestinal colic, nausea, vomiting, and/or diarrhea Physical exam skin erythema marginatum may be seen upper airway voice changes or horseness stridor shortness of breath gastrointestinal abdominal tenderness ascites signs of small bowel obstruction Studies Labs ↓ C4 and C2 levels normal C1q levels C1 inhibitor levels low level (hereditary angioedema type I) normal level (hereditary angioedema type II) Differential Drug-induced anaphylaxis Contact dermatitis Atopic dermatitis Superior vena cava syndrome Treatment Conservative securing airway, breathing, and circulation indication for the treatment of acute attacks of angioedema it is difficult to differentiate anaphylaxis and angioedema epinephrine, corticosteroids, and antihistamines are not effective in hereditary angioedema Medical plasma-derived C1 inhibitor indication acute treatment of herediatry angioedema short-term prophylaxis in patients with hereditary angioedema who will be exposed to a trigger (e.g., dental procedures and surgery) long-term prophylactic treatment of hereditary angioedema other medications that can be used in the acute treatment of hereditary angioedema includes plasma kallikrein inhibitorn (ecallantide) bradykinin receptor antagonist fresh frozen plasma attenuated androgens (e.g., danazol) indication for long-term prophylactic treatment of hereditary angioedema Complications Asphyxiation can result in death ≥ 30% mortality in patients with laryngeal angioedema can present with decreased inspiratory and expiratory rate and should be treated promptly w/epinephrine (histaminergic angioedema)