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 15 years. Physical examination reveals 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 severity?

Explanation

## Diagnosis of Byssinosis: Investigation of Choice **Key Point:** Spirometry with bronchodilator response is the investigation of choice for confirming byssinosis and assessing functional impairment. It demonstrates an obstructive pattern with potential reversibility, which is characteristic of this occupational lung disease. ### Pathophysiology of Byssinosis Byssinosis results from inhalation of endotoxins (lipopolysaccharides) from gram-negative bacteria colonizing cotton, flax, and hemp fibers. This causes: - Acute airway inflammation and bronchospasm - Chronic airway remodeling with fixed obstruction - Symptoms typically worse on the first day back to work ("Monday fever") ### Why Spirometry is the Gold Standard | Investigation | Role in Byssinosis | Utility | |---|---|---| | **Spirometry with bronchodilator** | Confirms obstructive pattern; reversibility indicates acute component | **Gold standard for functional assessment** | | HRCT chest | Shows advanced fibrosis; not diagnostic for early/mild disease | Useful for ruling out other pneumoconioses | | Serum ACE | Marker of granulomatous disease (sarcoidosis) | Not relevant to byssinosis | | BAL with differential | Shows neutrophilic inflammation; research tool | Not used for routine diagnosis | **High-Yield:** Spirometry findings in byssinosis: - **FEV₁/FVC ratio < 0.70** (obstructive pattern) - **Improvement ≥12% and ≥200 mL post-bronchodilator** (reversibility) - Progressive decline with continued exposure **Clinical Pearl:** The characteristic "Monday fever" (acute bronchospasm on return to work after weekend) is a clinical hallmark. Spirometry performed on Monday morning before work vs. after work may show acute decline, confirming work-relatedness. **Mnemonic: BYSSINOSIS Investigations — "SPIRO FIRST"** - **S**pirometry (functional test, obstructive pattern) - **P**eak flow variability (work-related decline) - **I**maging (HRCT for advanced disease) - **R**espiratory symptoms (history of Monday fever) - **O**ccupational exposure (15+ years cotton dust) [cite:Park 26e Ch 12]