Diagnosis: Mild Obstructive Lung Disease
This patient has mild obstructive lung disease based on an FEV1/FVC ratio of 75% (below the normal threshold of 78% predicted) with preserved FEV1 at 100% predicted, indicating early airway obstruction without significant functional impairment. 1
Interpretation of Pulmonary Function Tests
Obstructive Pattern Confirmed
- The FEV1/FVC ratio of 75% falls below the predicted value of 78%, meeting criteria for airflow obstruction 1
- The European Respiratory Society defines obstruction as a decreased FEV1/VC ratio with flows lower than expected over the volume range 1
- While some guidelines use a fixed threshold of <70%, this patient's ratio of 75% is abnormal when compared to their predicted value of 78% 1, 2
Severity Assessment
- FEV1 at 100% predicted indicates MILD obstruction - this is the key parameter for grading severity 3, 4
- The preserved FEV1 despite reduced FEV1/FVC ratio suggests early disease with minimal functional impairment 1
- FEF25-75% at 128% predicted is elevated, which can occur in mild obstruction and has limited clinical significance when FEV1 is normal 5
Additional Findings
- Normal lung volumes (VC 96% predicted) rule out restrictive disease 1
- Reduced respiratory muscle strength (MIP 56 cmH2O, MEP 104 cmH2O vs predicted 24 and 30 respectively) may indicate respiratory muscle weakness requiring further evaluation 1
- Normal PEFR at 105% predicted 5
Differential Diagnosis
Most Likely: Early COPD or Asthma
- If patient is a smoker with exposure history: Early COPD is most likely 1
- If younger patient with symptom variability: Asthma is more likely 1
- The key distinguishing feature is bronchodilator reversibility testing - improvement of >12% AND >200 mL in FEV1 indicates asthma 3
Critical Next Step
- Perform post-bronchodilator spirometry immediately to determine reversibility 1, 3
- Significant improvement (>12% and >200 mL increase in FEV1 or FVC) suggests reversible airflow obstruction consistent with asthma 3
- Lack of reversibility in a smoker suggests early COPD 1
Treatment Plan
If Bronchodilator Testing Shows Reversibility (Asthma)
- Initiate inhaled corticosteroid (ICS) as first-line controller therapy 3
- Add short-acting beta-agonist (SABA) as rescue medication 3
- Consider ICS/LABA combination if symptoms persist, though typically not needed for mild disease 6
If No Reversibility (Early COPD)
- Smoking cessation is the single most important intervention to prevent disease progression 1
- Consider long-acting bronchodilator (LABA or LAMA) if symptomatic 1
- Do NOT use ICS monotherapy for COPD 6
Address Respiratory Muscle Weakness
- The reduced MIP (56 cmH2O) and MEP (104 cmH2O) warrant evaluation for respiratory muscle dysfunction 1
- Consider inspiratory muscle training if symptomatic 1
- Evaluate for neuromuscular disease if weakness is disproportionate to lung disease 1
Common Pitfalls to Avoid
- Do not dismiss this as "normal" because FEV1 is 100% - the reduced FEV1/FVC ratio indicates definite obstruction 1, 4
- Do not use the fixed 70% threshold rigidly - this patient's ratio of 75% is abnormal relative to their predicted 78% 2, 7
- Do not start treatment without bronchodilator testing - reversibility determines whether asthma or COPD treatment is appropriate 3, 8
- Do not overlook the respiratory muscle weakness - this may contribute to symptoms and requires separate evaluation 1
- Do not assume submaximal effort - the consistent pattern across multiple parameters suggests true pathology, not poor technique 1
Follow-Up Monitoring
- Repeat spirometry in 3-6 months after initiating treatment to assess response 3
- Monitor FEV1 decline over time - rapid decline suggests need for treatment intensification 1, 4
- Annual spirometry to track disease progression 1
- Consider full pulmonary function testing with lung volumes and DLCO if diagnosis remains unclear or disease progresses 1, 8