A 24-year-old female athlete presents with recurrent episodes of dyspnea and biphasic stridor triggered by exercise and emotional stress. She has been treated for asthma for 2 years without improvement. Spirometry between episodes is normal, but during an acute episode, the flow-volume loop shows the pattern marked **A** in the diagram. Laryngoscopy during an acute episode reveals paradoxical adduction of the true vocal cords during inspiration. Which of the following is the most likely diagnosis?

Explanation

## Why Vocal cord dysfunction (paradoxical vocal fold motion) is right The flattened inspiratory limb (marked **A**) is the hallmark of variable extrathoracic obstruction. During forced inspiration, negative intraluminal pressure collapses the lesion further (Bernoulli effect), flattening the inspiratory portion of the flow-volume loop. The clinical presentation—young female athlete, exercise/stress triggers, biphasic stridor, normal spirometry between episodes, failure of asthma therapy, and laryngoscopic confirmation of paradoxical vocal cord adduction during inspiration—is pathognomonic for vocal cord dysfunction (VCD) or paradoxical vocal fold motion (PVFM). VCD is the most commonly missed diagnosis and frequent asthma mimic. The FIF50/FEF50 ratio is <1 due to the flattened inspiratory limb. Management is speech therapy and laryngeal control breathing exercises (Harrison 21e Ch 280; Murray Respiratory Medicine 7e Ch 27). ## Why each distractor is wrong - **Bilateral abductor vocal cord paralysis (Gerhardt syndrome)**: While this also causes variable extrathoracic obstruction with a flattened inspiratory limb, the laryngoscopic finding would show FIXED ABDUCTION of the cords (inability to abduct), not paradoxical ADDUCTION during inspiration. Gerhardt syndrome typically presents with stridor at rest and is not exercise-triggered. - **Intrathoracic tracheal stenosis**: This causes variable intrathoracic obstruction, which flattens the EXPIRATORY limb (not inspiratory) because positive pleural pressure during expiration compresses the intrathoracic airway. The flow-volume pattern would be opposite to that shown in **A**. - **Fixed laryngeal stenosis**: This produces a BOX-SHAPED flow-volume loop with BOTH inspiratory AND expiratory limbs flattened, not just the inspiratory limb. The laryngoscopic finding would show fixed narrowing, not paradoxical motion. **High-Yield:** Flattened inspiratory limb = extrathoracic obstruction; VCD/PVFM is the asthma mimic—diagnosis requires laryngoscopy during an acute episode showing paradoxical vocal cord adduction. [cite: Harrison 21e Ch 280; Murray Respiratory Medicine 7e Ch 27]