Vocal Cord Dysfunction / Inducible Laryngeal Obstruction (VCD/ILO) as a Mimic of Anaphylaxis: A Retrospective Cohort Study

BACKGROUND: Vocal cord dysfunction (VCD), or inducible laryngeal obstruction (ILO), is an episodic upper airway disorder that can mimic anaphylaxis. OBJECTIVE: To determine the prevalence of VCD/ILO among adults referred to allergy clinic for suspected anaphylaxis and to identify clinical markers that distinguish VCD/ILO from anaphylaxis. METHODS: We conducted a retrospective study of adults referred for suspected anaphylaxis to a tertiary allergy clinic in Newcastle, Australia, in 2023. Patients were classified as confirmed VCD/ILO (laryngoscopy-proven), suspected VCD/ILO (spirometry findings or high clinical suspicion after exclusion of alternate diagnoses), anaphylaxis, or other. Demographics, triggers, comorbidities, clinical features, investigations, and health care utilization were compared between laryngoscopy-confirmed VCD/ILO and anaphylaxis. RESULTS: Among 133 adults, 11 (8.3%) had laryngoscopy-confirmed VCD/ILO. Inclusion of suspected cases (n = 21 [15.8%]) increased prevalence of VCD/ILO to 24.1% (n = 32). Compared with anaphylaxis, VCD/ILO was characterized by predominant upper airway symptoms, including throat tightness (100% vs 53.8%, P = .004), stridor (36.4% vs 1.9%, P = .003), dysphonia (72.7% vs 17.3%, P < .001), and cough (54.5% vs 1.9%, P < .001) with fewer systemic symptoms (urticaria 18.2% vs 84.6%, P < .001; gastrointestinal 9.1% vs 44.2%, P = .04; cardiovascular 0% vs 55.8%, P < .01). Multiple triggers were more common in VCD/ILO (72.7% vs 1.9%, P < .001), particularly aerosolized chemicals (36.4% vs 0%, P < .001). IgE sensitization to the proposed trigger was uncommon (9.1% vs 63.5%, P < .008) in VCD/ILO. CONCLUSIONS: VCD/ILO is a frequent differential diagnosis in adults referred for anaphylaxis. Recognition of its characteristic clinical features and trigger profiles may prevent misdiagnosis, reduce health care utilization, and improve patient outcomes.