Laryngoscopy During Exercise is the Next Test
A 17-year-old with a flattened inspiratory flow loop on PFT should undergo flexible laryngoscopy during exercise (continuous laryngoscopy exercise test) to confirm the diagnosis of exercise-induced laryngeal dysfunction (EILD), also known as vocal cord dysfunction. 1, 2
Why This Finding Points to Upper Airway Dysfunction
- A flattened inspiratory flow loop with normal expiratory parameters is a hallmark sign of upper airway or laryngeal obstruction, not asthma or lower airway disease 3, 1
- The pattern specifically suggests variable extrathoracic obstruction, where the negative intraluminal pressure during inspiration cannot be opposed by atmospheric pressure surrounding the extrathoracic airways, leading to dynamic collapse or paradoxical vocal cord adduction 3
- This contrasts sharply with asthma, which produces expiratory flow limitation and a characteristic scooped-out expiratory curve 3
The Gold Standard Diagnostic Test
- Flexible laryngoscopy performed during exercise challenge is the gold standard for diagnosing exercise-induced laryngeal dysfunction, allowing direct visualization of paradoxical vocal cord adduction or other laryngeal abnormalities during symptomatic periods 1
- Continuous laryngoscopy during exercise provides definitive diagnosis by capturing the dynamic laryngeal movements that occur specifically during exertion 1
- The European Respiratory Society emphasizes that while flow-volume loops alert clinicians to possible upper airway obstruction, endoscopic techniques are the necessary next step to confirm the dysfunction 3
Clinical Context Supporting This Diagnosis
- Exercise-induced laryngeal dysfunction is particularly common in adolescent athletes, making this age group a high-risk population 1
- Key clinical features that would support this diagnosis include:
- Dyspnea and throat tightness occurring during peak exercise rather than 5-20 minutes after exercise (which would suggest exercise-induced bronchoconstriction) 2
- Inspiratory stridor with throat tightness that resolves within approximately 5 minutes of stopping activity 2
- Poor or absent response to standard asthma medications including beta-2 agonists 1, 2
Why Other Tests Are Not the Answer
- Bronchoscopy alone would be appropriate for evaluating intrathoracic airway obstruction or tracheomalacia, but the flattened inspiratory loop specifically points to extrathoracic pathology 3
- Methacholine challenge testing is used to diagnose airway hyperreactivity in asthma, but this patient's inspiratory flow pattern argues against lower airway disease 3
- CT imaging could identify structural abnormalities but would not capture the dynamic, exercise-induced nature of vocal cord dysfunction 3
Important Caveats
- Exercise-induced laryngeal dysfunction can coexist with exercise-induced bronchoconstriction in 20-40% of cases, so finding laryngeal dysfunction does not completely exclude asthma 2
- The laryngoscopy must be performed during exercise when symptoms are provoked, as the vocal cords may appear completely normal at rest 1
- If laryngoscopy during exercise is not available, combined procedures including upper endoscopy and rigid laryngobronchoscopy should be considered to evaluate for structural abnormalities 3