A 38-year-old male worker in a textile mill presents with progressive dyspnea, dry cough, and chest tightness for 6 months. He has been exposed to cotton dust for 12 years. Clinical examination reveals bilateral fine crackles at lung bases. Chest X-ray shows bilateral lower lobe interstitial opacities. Which investigation is most appropriate to confirm the diagnosis of byssinosis and assess disease severity?

Explanation

## Investigation of Choice for Byssinosis ### Diagnosis and Pathophysiology Byssinosis is an occupational lung disease caused by inhalation of cotton, flax, or hemp dust. It presents with airway obstruction and inflammation, not primarily parenchymal fibrosis. ### Why Spirometry with Bronchodilator Reversibility is Best **Key Point:** Spirometry is the gold standard functional investigation for byssinosis because it: 1. Detects obstructive pattern (FEV₁/FVC ratio <70%) 2. Demonstrates reversibility with bronchodilators (≥12% and ≥200 mL improvement in FEV₁), confirming airway obstruction rather than fixed fibrosis 3. Quantifies disease severity using GOLD criteria 4. Monitors disease progression and treatment response **High-Yield:** The characteristic finding in byssinosis is **Monday morning symptom** (acute bronchospasm on return to work after weekend) with reversible airway obstruction — spirometry captures this functional deficit. ### Comparison of Investigations | Investigation | Role in Byssinosis | Limitation | |---|---|---| | **Spirometry + bronchodilator** | Gold standard; detects reversible obstruction | — | | HRCT chest | Shows parenchymal changes (fibrosis); useful if mixed pattern suspected | Byssinosis is primarily obstructive, not fibrotic | | Serum ACE | Marker for sarcoidosis/granulomatous disease | Byssinosis is non-granulomatous | | BAL | Research tool; identifies dust particles | Not diagnostic; not standard clinical practice | **Clinical Pearl:** Byssinosis differs from silicosis and asbestosis in that it causes **reversible airway obstruction** rather than progressive fibrosis. This distinction makes spirometry with bronchodilator response the key diagnostic test. ### Staging of Byssinosis (Based on Spirometry) - **Grade 0:** Normal FEV₁, no symptoms - **Grade ½:** Occasional symptoms on first day back - **Grade 1:** Symptoms every first day back - **Grade 2:** Symptoms on first and other days - **Grade 3:** Permanent airflow obstruction (FEV₁ <80% predicted)