What is the next step in diagnosing a 17-year-old cross country runner with episodic shortness of breath and chest tightness, exercising-induced asthma, and a pulmonary function test (PFT) showing a flattened inspiratory flow loop despite normal expiratory findings, normal Forced Expiratory Volume in one second (FEV1), and normal Forced Vital Capacity (FVC)?

Diagnosing Exercise-Induced Laryngeal Dysfunction in a Cross Country Runner

The next step in diagnosing this 17-year-old cross country runner with a flattened inspiratory flow loop should be flexible laryngoscopy during exercise to evaluate for exercise-induced laryngeal dysfunction (EILD). 1

Clinical Picture Analysis

The patient presents with several key findings that point toward exercise-induced laryngeal dysfunction rather than exercise-induced bronchoconstriction (EIB):

• Episodic shortness of breath and chest tightness during exercise 1
• Poor response to asthma prevention medications 1
• Normal expiratory findings on pulmonary function test 1
• Normal FEV1 and FVC values 1
• Flattened inspiratory flow loop 1

Diagnostic Algorithm

1. Recognize the pattern: A flattened inspiratory flow loop with normal expiratory parameters strongly suggests upper airway/laryngeal dysfunction rather than asthma 1

2. Confirm with direct visualization: Flexible laryngoscopy during exercise is the gold standard for diagnosing EILD 1

   • This allows direct observation of vocal cord adduction or other laryngeal abnormalities that only appear during symptomatic periods 1
   • Continuous laryngoscopy during exercise challenge provides definitive diagnosis 1

3. Consider additional testing if laryngoscopy is not immediately available:

   • Video recording of the patient during exercise when inspiratory stridor is heard 1
   • Exercise challenge test with careful attention to timing of symptoms (EILD symptoms peak during exercise, while EIB peaks 5-20 minutes after stopping) 1

Differential Diagnosis

The patient's presentation suggests one of several types of exercise-induced laryngeal dysfunction:

• Paradoxical vocal cord dysfunction (VCD) 1
• Exercise-induced laryngeal prolapse 1
• Exercise-induced laryngomalacia 1
• Arytenoid collapse variants 1

These conditions are particularly common in adolescent athletes and can coexist with EIB, but require different management approaches 1.

Key Diagnostic Clues

• Flattening of the inspiratory curve on spirometry is a hallmark sign of EILD 1, 2
• Failure to respond to standard asthma management is a key historical feature suggesting EILD 1
• The timing of symptoms (during vs. after exercise) helps differentiate EILD from EIB 1
• EILD is more common in middle school to high school-aged athletes than college-aged athletes 1

Common Pitfalls to Avoid

• Misdiagnosing EILD as refractory asthma and continuing ineffective treatments 1, 3
• Relying solely on spirometry without direct visualization of the larynx during symptoms 1, 2
• Failing to recognize that EILD and EIB can coexist in the same patient 1
• Not considering EILD when asthma treatments fail to improve symptoms 3, 4

Importance of Correct Diagnosis

Proper diagnosis is critical because:

• EILD will not respond to traditional asthma medications like β2-agonists 1
• Untreated EILD can significantly impact athletic performance and quality of life 1
• Appropriate treatment approaches differ substantially from asthma management 1, 3
• Continuous misdiagnosis leads to unnecessary medication exposure and delayed appropriate therapy 3

Flexible laryngoscopy during exercise remains the definitive diagnostic test for confirming EILD in this clinical scenario 1.