What is the most likely diagnosis for a previously healthy female teenage student with no past medical history, who experiences chest tightness, wheezing, shortness of breath, and produces pink frothy sputum after running, culminating in syncope?

Most Likely Diagnosis: Post-Obstructive Pulmonary Edema Secondary to Exercise-Induced Laryngospasm

The most likely diagnosis in this previously healthy teenage female is post-obstructive pulmonary edema (POPE) triggered by exercise-induced laryngospasm, given the combination of exercise-triggered symptoms, syncope, and the pathognomonic finding of pink frothy sputum. 1

Critical Diagnostic Features

The clinical presentation contains several key elements that point away from simple exercise-induced asthma and toward a more serious airway obstruction:

• Pink frothy sputum is the definitive clue - this is the hallmark of pulmonary edema, not asthma 1
• Syncope following exercise-induced respiratory symptoms - suggests complete or near-complete airway obstruction rather than bronchospasm 1
• Previously healthy with sudden onset - makes chronic cardiac or pulmonary disease unlikely 1
• Progressive worsening with increased exercise intensity (200m → 400m) - consistent with exercise-induced upper airway obstruction 2

Pathophysiology of Post-Obstructive Pulmonary Edema

POPE occurs when forceful inspiratory efforts against an obstructed airway create extreme negative intrathoracic pressure, causing non-cardiogenic pulmonary edema. 1 The mechanism involves:

• Negative pleural pressures increase the hydrostatic pressure gradient across pulmonary capillary walls, forcing fluid into the interstitial space 1
• Laryngospasm is the most common cause (>50% of cases) 1
• More common in young, muscular adults with male:female ratio of 4:1, though females are certainly affected 1
• The condition presents with dyspnea, agitation, cough, pink frothy sputum, and low oxygen saturations 1

Why Not Exercise-Induced Asthma?

While exercise-induced asthma could explain chest tightness and wheezing after running 1, 2, several features argue strongly against this diagnosis:

• Asthma does not cause pink frothy sputum - asthma produces clear or white mucus, not the pink frothy sputum characteristic of pulmonary edema 1
• Syncope is extremely rare in asthma - while severe asthma can cause hypoxia, syncope suggests complete airway obstruction 1
• The rapid progression to syncope within one hour - suggests acute complete obstruction rather than progressive bronchospasm 1

Why Not Cardiac Asthma or Flash Pulmonary Edema?

Cardiac causes of pulmonary edema are unlikely in this previously healthy teenager:

• Flash pulmonary edema typically occurs with hypertensive urgency and diastolic dysfunction - not in healthy teenagers during exercise 3, 4
• Cardiac asthma occurs in patients with congestive heart failure - this patient has no history of heart disease 5
• Exercise-induced syncope in cardiac disease (hypertrophic cardiomyopathy, aortic stenosis) would likely present with other cardiac symptoms and would not resolve spontaneously in 3 minutes 1

Differential Considerations

The differential diagnosis should include:

• Exercise-induced laryngeal obstruction/vocal cord dysfunction - can cause similar symptoms but typically doesn't progress to complete obstruction with syncope 2, 6
• Exercise-induced laryngomalacia - possible but less likely to cause complete obstruction and pulmonary edema 6
• Severe exercise-induced bronchospasm - would not explain pink frothy sputum 1

Clinical Management Priorities

Immediate management should focus on:

• Airway assessment and oxygen supplementation - ensure airway patency and adequate oxygenation 1
• Supportive care for pulmonary edema - POPE typically resolves within hours with supportive treatment 1
• Avoid unnecessary interventions - diuretics are not indicated for non-cardiogenic pulmonary edema 1
• Monitor for complications - death is rare but usually attributable to hypoxic brain injury during the obstruction episode 1

Diagnostic Workup

Essential investigations include:

• Chest radiograph - will show bilateral alveolar opacities consistent with pulmonary edema 1
• Arterial blood gas - to assess oxygenation and acid-base status 3
• ECG and cardiac evaluation - to exclude cardiac causes in a teenager with syncope 1
• Laryngoscopy when stable - to evaluate for structural airway abnormalities or vocal cord dysfunction 2, 6

Prognosis and Follow-up

Prompt diagnosis and management usually result in clinical and radiological resolution within a few hours, though delayed presentation up to 2.5 hours has been described 1. The patient will require:

• ENT/pulmonology referral - to identify the underlying cause of laryngospasm and prevent recurrence 2, 6
• Exercise testing under controlled conditions - to reproduce symptoms and confirm diagnosis 2
• Education about warning signs - to seek immediate help if symptoms recur 1