A 38-year-old woman with a 5-year history of episodic dyspnea and cough presents for spirometry. Results show FEV₁/FVC ratio of 0.72 (pre-bronchodilator), FEV₁ 82% predicted, and FVC 85% predicted. Post-bronchodilator FEV₁ increases to 91% predicted with FEV₁/FVC ratio of 0.78. She reports symptoms worse in the morning and after exposure to dust. What is the most appropriate next step in management?

Explanation

## Clinical Presentation and Spirometry Interpretation This patient presents with: - Episodic dyspnea and cough - Morning symptoms and dust-triggered exacerbations - **Spirometry showing reversible airflow obstruction** (FEV₁ increases 9% post-bronchodilator) ## Spirometry Pattern Analysis | Parameter | Pre-BD | Post-BD | Interpretation | |-----------|--------|---------|----------------| | FEV₁/FVC | 0.72 | 0.78 | Borderline low, improves with BD | | FEV₁ | 82% | 91% | **>12% and >200 mL improvement** | | FVC | 85% | — | Normal | | Pattern | — | — | **Reversible obstruction** | **Key Point:** A post-bronchodilator FEV₁ improvement of **≥12% AND ≥200 mL** is diagnostic of reversible airflow obstruction, consistent with asthma, not COPD. ## Diagnostic Algorithm for Suspected Asthma ```mermaid flowchart TD A[Episodic dyspnea + cough]:::outcome --> B{Spirometry reversible?}:::decision B -->|Yes| C[Asthma likely]:::outcome C --> D{Baseline spirometry normal?}:::decision D -->|Yes| E[Perform bronchial challenge]:::action E --> F[Methacholine or histamine test]:::action F --> G[Positive = airway hyperresponsiveness]:::outcome B -->|No| H[Consider COPD or other diagnosis]:::outcome ``` **High-Yield:** When spirometry shows **reversibility** (≥12% improvement in FEV₁ post-BD) but **baseline values are normal**, the next step is **bronchial challenge testing** to demonstrate airway hyperresponsiveness and confirm asthma diagnosis. **Clinical Pearl:** Methacholine challenge is most useful in patients with: - Reversible obstruction on spirometry (as in this case) - Normal or near-normal baseline FEV₁ - Suggestive symptoms but no obstruction at rest - High pre-test probability of asthma ## Why Methacholine Challenge Is Appropriate Here 1. **Reversibility confirmed**: Post-BD improvement rules out fixed obstruction (COPD). 2. **Baseline FEV₁ normal**: Allows safe performance of challenge test (contraindicated if FEV₁ <60% predicted). 3. **High sensitivity for asthma**: Positive methacholine test (PC₂₀ <16 mg/mL) confirms airway hyperresponsiveness. 4. **Negative test has high NPV**: Rules out asthma if clinical suspicion is moderate. ## Why Not the Other Options? **Inhaled corticosteroid monotherapy (Option A):** Premature treatment initiation before confirming asthma diagnosis. ICS should follow confirmed diagnosis, not precede it. Moreover, monotherapy without a long-acting bronchodilator is suboptimal for persistent asthma. **High-resolution CT (Option C):** Not indicated in a patient with reversible obstruction and normal lung volumes. ILD presents with restriction (low FVC, normal or high FEV₁/FVC ratio), not reversible obstruction. **Bronchoscopy (Option D):** No clinical indication. Endobronchial lesions present with fixed obstruction (no reversibility), not reversible obstruction. Bronchoscopy is reserved for hemoptysis, suspected malignancy, or recurrent infections.