What is the diagnosis and management plan for a patient with impaired lung function, as indicated by an FEV1 of 81, FVC of 67, and an FEV1/FVC ratio of 100, suggestive of a restrictive lung disease pattern?

Spirometric Pattern Analysis and Management

Primary Interpretation

This spirometric pattern (FEV1 81%, FVC 67%, FEV1/FVC 100%) suggests a restrictive ventilatory defect, but confirmation with total lung capacity (TLC) measurement is essential before making a definitive diagnosis. 1

Understanding the Pattern

The key features of this spirometry are:

• Reduced FVC (67% predicted) - below the 5th percentile threshold 1
• Mildly reduced FEV1 (81% predicted) - approaching normal range 1
• Elevated FEV1/FVC ratio (100%) - well above the normal threshold of 70-80% 1

This pattern is highly suggestive but not diagnostic of restrictive lung disease. 1

Critical Diagnostic Caveat

A reduced FVC with normal or elevated FEV1/FVC ratio does NOT prove restrictive lung disease - it is associated with a low TLC only about 50% of the time. 1 The positive predictive value of this spirometric pattern for true restriction is only 58%, meaning nearly half of patients with this pattern will have normal lung volumes. 2

Common Alternative Explanations for This Pattern:

• Submaximal effort - incomplete inhalation or exhalation during testing 1
• Neuromuscular weakness - inability to fully inspire or expire 1
• Patchy peripheral airflow obstruction - early small airway collapse 1
• Obesity without true lung restriction 3
• Congestive heart failure 3

Mandatory Next Step

TLC measurement via body plethysmography or helium dilution is required to confirm true restrictive lung disease. 1

• True restriction is defined as TLC < 5th percentile of predicted 1
• Do NOT use single-breath VA from DLCO testing to assess TLC, as this systematically underestimates lung volumes 1
• Body plethysmography is preferred but may not be feasible in patients with severe weakness or wheelchair dependence 1

Differential Diagnosis Based on TLC Results

If TLC is Reduced (True Restriction):

Clinical diagnoses with highest positive predictive value (≥90%) for restriction: 3

• Pulmonary fibrosis/interstitial lung disease
• Pleural disease (effusion, thickening, fibrosis)
• Chest wall disease (kyphoscoliosis, thoracoplasty)
• Neuromuscular disorders

Additional testing to consider: 1

• DLCO measurement to assess gas exchange impairment
• High-resolution CT chest for interstitial lung disease
• Respiratory muscle strength testing if neuromuscular disease suspected
• Overnight oximetry or arterial blood gas

If TLC is Normal (Nonspecific Pattern):

Most common causes of this "pseudorestriction": 3, 4

• Early or mild obstructive disease with air trapping
• Obesity without true lung restriction
• Congestive heart failure
• Bronchiolitis
• Poor effort or coordination during testing 1

Management approach: 1

• Repeat spirometry with careful coaching for maximal effort
• Consider bronchodilator trial (400 mcg salbutamol, reassess after 15 minutes) 5
• Measure slow vital capacity (inspiratory or expiratory) which may be more accurate than FVC 1
• Clinical correlation with symptoms, imaging, and comorbidities is essential 4

Severity Assessment

If restriction is confirmed, severity is graded by FEV1 % predicted: 1

• Mild: FEV1 70-80% predicted
• Moderate: FEV1 60-69% predicted
• Moderately severe: FEV1 50-59% predicted
• Severe: FEV1 35-49% predicted
• Very severe: FEV1 <35% predicted

This patient's FEV1 of 81% would indicate mild impairment if restriction is confirmed. 1

Prognostic Implications

Restrictive lung dysfunction is an independent predictor of increased all-cause and cardiovascular mortality. 6 The mortality risk increases with:

• Lower FVC % predicted values 6
• Presence of protein-energy wasting, inflammation, or cardiovascular comorbidities 6
• Progressive decline in lung volumes over time 1

Clinical Pitfalls to Avoid

• Never diagnose restriction based on spirometry alone - TLC measurement is mandatory 1
• Do not assume poor effort without careful observation - neuromuscular weakness can produce identical patterns 1
• Avoid using fixed FEV1/FVC cutoffs - use 5th percentile of predicted to avoid age-related misclassification 1
• Do not rely on single-breath VA from DLCO as a substitute for proper TLC measurement 1
• Recognize that normal spirometry does not exclude significant lung disease - only 2.4% of patients with normal FVC have restriction, but gas exchange abnormalities may still be present 2