Distinguishing between anaphylaxis and bradykinin-mediated angioedema can be difficult in the acute setting, particularly when airway compromise dominates the presentation. Recognition is crucial, as management strategies differ substantially. An 84-year-old woman presented to the Emergency Department in Preston with rapidly progressive swelling of the lips, tongue, and neck, accompanied by dysphagia and a hoarse voice. She had self-administered multiple doses of an adrenaline autoinjector before arrival. On examination, she was hemodynamically stable and afebrile, with marked tongue and floor-of-mouth edema but no urticaria or pruritus. Considering refractory anaphylaxis, she received intravenous dexamethasone, an adrenaline nebulizer, and an adrenaline infusion. ENT and ICU teams were involved; flexible nasendoscopy confirmed edema of the floor of the mouth and arytenoids, with mild epiglottic involvement but an adequate glottic opening. This episode followed several similar admissions since 2022, each previously treated as anaphylaxis with limited response to adrenaline. Further investigation revealed normal mast-cell tryptase (6.1 µg/L) and persistently low C4 (<0.03 g/L) with normal C3 (1.29 g/L), findings consistent with C1-esterase inhibitor (C1-INH) deficiency. Given her history of CD5-negative low-grade B-cell lymphoproliferative disorder, a diagnosis of acquired angioedema was made following multidisciplinary review, and treatment with icatibant was initiated. This case highlights the importance of considering bradykinin-mediated angioedema in patients with recurrent "refractory anaphylaxis." The absence of urticaria, normal tryptase, and low complement levels should prompt evaluation for C1-INH deficiency, allowing timely, targeted management and improved outcomes.

Bradykinin-mediated angioedema comprises rare but potentially life-threatening disorders, most notably hereditary angioedema (HAE) due to C1 inhibitor (C1-INH) deficiency or dysfunction. Diagnosis is often difficult, as these conditions can resemble urticaria variants, leading to misdiagnosis and delays in care. Distinguishing features are critical, since bradykinin-mediated forms do not respond to antihistamines or corticosteroids. This review summarizes the differential diagnoses of angioedema, including urticaria variants, cheilitis granulomatosa, and hypocomplementemic urticarial vasculitis, highlighting clinical and diagnostic clues. Particular focus is given to HAE-its subtypes (Type I, Type II, and normal C1-INH), pathophysiology, presentation, and genetic basis. Acquired angioedema and drug-induced forms, such as ACE inhibitor-associated angioedema, are also discussed. The therapeutic landscape is rapidly evolving, spanning acute and prophylactic approaches. Options include C1-INH concentrate, kallikrein inhibitors, bradykinin receptor antagonists, and factor XII inhibitors. While these advances expand treatment opportunities, they also complicate decision-making for patients and physicians. Furthermore, emerging CRISPR-based gene editing therapies represent innovative approaches that pose complex ethical dilemmas, and their long-term safety and efficacy have yet to be established. Although novel therapies reduce attack frequency, their true impact on quality of life is not fully established. Comparative effectiveness data are limited, long-term safety-particularly of gene-based therapies-is unknown, and the real-world utility of new oral on-demand agents for acute therapy is uncertain, especially in severe pharyngeal or laryngeal attacks that may hinder swallowing. Current guidelines remain unclear on the need for short-term prophylaxis in patients already receiving effective long-term prophylactic therapy. In conclusion, despite major therapeutic advances, persistent challenges and unanswered questions underscore the need for pragmatic, patient-centered, long-term studies to optimize care.

Background and Clinical Significance: Acquired angioedema (AAE) is a rare and potentially life-threatening condition characterized by acquired deficiency of C1-inhibitor (C1-INH) resulting in hyperactivation of the classical complement pathway. AAE occurs in association with malignancies or autoimmune diseases. Infectious triggers are rarely encountered, and the underlying mechanisms have yet to be completely clarified. Case Presentation: This case involves a previously healthy 19-year-old male who was admitted with Mycoplasma pneumonia and oral ulcers, subsequently developing unilateral facial angioedema. Laboratory studies demonstrated reduced C4, decreased levels and activity of C1-INH, and reduced C1q, all consistent with acquired C1-INH deficiency. These findings were attributed to the presence of cold agglutinins, which are frequently observed in Mycoplasma pneumoniae infections. Following treatment with icatibant, a bradykinin B2 receptor antagonist, the patient's angioedema resolved rapidly. An exhaustive workup found no evidence of underlying systemic disorders, and the patient did not experience any angioedema attacks following resolution of the infection. Conclusions: The presence of cold agglutinins, commonly associated with Mycoplasma infections, can precipitate a decline in C1-INH levels, resulting in complement pathway dysregulation. This disruption leads to an excess of bradykinin, followed by increased vascular permeability and localized edema.

Angioedema due to acquired C1-inhibitor deficiency (AAE-C1INH) is a rare disorder characterized by recurrent episodes of angioedema due to excessive bradykinin release. Deucrictibant, an oral B2 receptor antagonist, is currently under development for long-term prophylactic and on-demand treatment in hereditary angioedema. In a recent small double-blind, placebo-controlled crossover trial (EudraCT no. 2021-000720-36), all 3 participants with AAE-C1INH had complete control of angioedema during 8 weeks of treatment with deucrictibant immediate-release capsule. We investigated the long-term efficacy and safety of deucrictibant extended-release tablet as prophylactic treatment in patients with AAE-C1INH. In this open-label, single-arm study, patients with AAE-C1INH received deucrictibant 40 mg extended-release tablet once daily. The primary end point was the time-normalized number of investigator-confirmed angioedema attacks per 28 days of exposure to deucrictibant compared to baseline. Four patients with AAE-C1INH were enrolled, 3 of whom were rolled over from the randomized controlled trial of immediate-release deucrictibant. The on-treatment follow-up duration in this study ranged from 563 to 612 days. The mean monthly attack rates at baseline were 1.2, 1.2, 0.9, and 2.1, respectively (mean, 1.35). One mild abdominal attack was reported by one patient 2 days after initiation of deucrictibant treatment; the remaining patients were attack-free during the treatment period. The mean monthly angioedema attack rate for all patients was 0.01. No treatment-related adverse events were reported. Deucrictibant extended-release tablet effectively prevented angioedema attacks in patients with AAE-C1INH, with no safety concerns.

Acquired angioedema due to C1-inhibitor deficiency (AAE-C1INH) is a rare condition characterized by the localized swelling of the deeper skin layers and mucous membranes, especially the face, lips, tongue, throat, and gastrointestinal tract. AAE-C1INH is strongly associated with lymphoproliferative disorders, although it can also be linked to autoimmune conditions, solid tumors, infections, or even occur without an identifiable cause. We present the case of a 45-year-old female patient with complaints of recurrent abdominal pain, bloating, and joint swelling. Laboratory testing showed decreased C1q and C4 complement levels, and C1 esterase inhibitor levels, indicative of AAE-C1INH. Further work up confirmed a diagnosis of extranodal marginal zone lymphoma with involvement of the bone marrow and spleen. Treatment with rituximab led to resolution of angioedema symptoms and almost complete remission of underlying lymphoma. This case underscores the importance of evaluating an underlying lymphoproliferative disorder in AAE-C1INH. Therefore, the early participation of a multidisciplinary team including specialists in immunology, hematology, and oncology is necessary for appropriate management.