Objective: Vocal cord dysfunction (VCD) often presents with dramatic and abrupt symptoms. To diagnose VCD, visualization by direct laryngoscopy is required and because patients are usually asymptomatic, a specific method to provoke VCD is needed. Approaches to predict VCD by alterations of the flow-volume loop have been investigated.

Methods: Adolescents with clinical suspicion of VCD were invited to participate. After an initial pulmonary function test (PFT), direct laryngoscopy was performed. This was followed by a methacholine challenge test (MCT); the methacholine dose causing a 20% drop in forced expiratory volume after 1 sec (FEV(1) ) (PD(20) FEV(1) ) was calculated. Then a second laryngoscopy was conducted. PFT changes before and after MCT were compared with the data of 14 healthy controls (HCs).

Results: Thirty-five patients (8-19 years) were investigated. Three showed anatomical alterations. Of the remaining 32 patients, 14 had VCD and 18 had bronchial hyperresponsiveness (non-VCD). In 29 patients with a positive MCT, PD(20) FEV(1) methacholine was significantly lower in VCD compared with non-VCD (VCD 0.24 ± 0.4 mg, non-VCD 0.73 ± 0.73 mg, P = 0.0006). A PD(20) FEV(1)  < 0.24 mg methacholine predicted VCD with a sensitivity of 85% and a specificity of 75%. VCD patients showed significantly lower PFT parameters after challenge; FEV(1) : VCD 58.5 ± 20.1%, non-VCD 80.2 ± 18.0%, and HCs 98.7 ± 16.6% (P < 0.0001).

Conclusions: The combination of MCT and laryngoscopy may be able to differentiate between VCD and non-VCD. VCD patients showed a positive reaction at lower methacholine doses and displayed greater airway obstruction after MCT. PFTs and MCT do not replace direct laryngoscopy in the diagnosis of VCD in adolescents.