A 58-year-old man with a 10-year history of "asthma" presents with progressive dyspnea, chronic cough, and monophonic wheeze that has worsened despite high-dose inhaled corticosteroids and long-acting bronchodilators. His flow-volume loop shows a flattened expiratory limb with a normal inspiratory loop. The pattern marked **D** in the diagram suggests an intrathoracic airway lesion. Which of the following is the MOST appropriate next diagnostic step to identify the underlying cause?

Explanation

## Why Flexible bronchoscopy with biopsy is right The flow-volume loop pattern marked **D** — flattened expiratory limb with normal inspiratory loop — is pathognomonic for variable intrathoracic obstruction. This occurs because positive intrathoracic pressure during forced expiration compresses the intrathoracic airway, causing flow limitation. The clinical presentation of "asthma" unresponsive to standard bronchodilator therapy, combined with monophonic wheeze and this characteristic flow-volume pattern, mandates direct visualization of the airway. Flexible bronchoscopy is the gold standard diagnostic tool (Harrison 21e Ch 287) — it allows direct visualization of the intrathoracic trachea and mainstem bronchi, enables tissue biopsy if a lesion is identified (critical for ruling out intrathoracic tracheal tumor, including squamous cell carcinoma or adenoid cystic carcinoma), and can identify other causes such as tracheomalacia, foreign body, or bronchogenic carcinoma invading the airway. This patient's long-standing "asthma" that is refractory to standard therapy is a classic presentation for intrathoracic airway obstruction being misdiagnosed as asthma. ## Why each distractor is wrong - **High-dose oral corticosteroids for 2 weeks**: This perpetuates the misdiagnosis of asthma and delays identification of a potentially serious structural lesion (tumor, tracheomalacia, or foreign body). Corticosteroids will not address the underlying mechanical obstruction and may delay diagnosis of malignancy. - **Empiric trial of omalizumab (anti-IgE therapy)**: This is inappropriate escalation of asthma therapy without first excluding structural airway disease. The flow-volume loop pattern is not consistent with asthma and mandates anatomic evaluation before biologic immunotherapy. - **Repeat spirometry after inhaled albuterol challenge**: Repeating PFTs without first obtaining imaging or bronchoscopy is redundant and delays diagnosis. The abnormal flow-volume loop pattern already indicates the need for direct airway visualization, not further functional testing. **High-Yield:** Variable intrathoracic obstruction (flattened expiratory limb on flow-volume loop) + "asthma" refractory to bronchodilators = think intrathoracic tracheal tumor, tracheomalacia, or foreign body → flexible bronchoscopy is gold standard. [cite: Harrison 21e Ch 287; SME anchor: variable intrathoracic obstruction diagnostic algorithm]