Emphysema (Answer: B)
The most likely diagnosis is emphysema, given the combination of significant smoking history, increased anteroposterior chest diameter with hyperresonance (indicating hyperinflation), high lung capacity with increased residual volume on PFTs, and irreversible airflow obstruction (FEV1 60% not responding to bronchodilators). 1
Clinical Reasoning
Key Diagnostic Features Supporting Emphysema/COPD
Smoking history: An 18-year smoking history in a 45-year-old patient is a primary risk factor for COPD, with most patients being long-term cigarette smokers 1
Physical examination findings: The increased AP diameter and hyperresonance on percussion are classic signs of chronic overinflation and air trapping, which indicate emphysematous changes 1, 2
Pulmonary function tests: The combination of high lung capacity, increased residual volume (RV), and FEV1 of 60% represents moderate airflow obstruction with hyperinflation 3. The lack of bronchodilator response (minimal reversibility) strongly favors COPD over asthma 1
Symptoms: Exertional shortness of breath and chronic cough for 5 months are cardinal symptoms of COPD, typically developing gradually and eventually limiting daily activities 1, 2
Why Not the Other Options
Lung fibrosis (Option A): This diagnosis is inconsistent with the PFT findings. Fibrotic lung diseases produce restrictive patterns with reduced lung volumes and capacities, not the high lung capacity and increased RV seen in this patient 4. Additionally, fibrosis would show a normal or increased FEV1/FVC ratio, not the obstructive pattern implied here.
Bronchiectasis (Option C): While bronchiectasis can cause chronic cough and crackles, it typically presents with persistent large volumes of purulent sputum (>30 mL per 24 hours) 1. The PFT pattern of high lung capacity with increased RV and lack of bronchodilator response is more characteristic of emphysema. Bronchiectasis has been specifically excluded from the COPD definition by convention 1.
Allergic pneumonitis (Option D): This would typically present with a restrictive pattern on PFTs (reduced lung volumes), not the obstructive pattern with hyperinflation seen here. Additionally, there is no mention of relevant environmental or occupational exposures typical of hypersensitivity pneumonitis.
Important Clinical Context
Rheumatoid Arthritis Consideration
The patient's long-standing rheumatoid arthritis is relevant but does not change the primary diagnosis. While RA can be associated with various pulmonary manifestations, the clinical presentation and PFT pattern overwhelmingly point to smoking-related emphysema as the primary pathology 1.
Diagnostic Confirmation
- Post-bronchodilator spirometry showing FEV1/FVC ratio <0.70 would definitively confirm COPD 2, 5, 4
- The lack of bronchodilator response distinguishes COPD from asthma, where marked improvement with bronchodilators would be expected 1
- Evidence of emphysema on imaging, decreased diffusing capacity, and chronic hypoxemia would further support the COPD diagnosis 1
Common Pitfall
Physical signs alone are poor guides to the severity of airflow limitation, and their absence does not exclude COPD 1, 2. However, when present—as in this case with increased AP diameter and hyperresonance—they are useful indicators of significant disease with hyperinflation 1.