Restrictive Lung Disease Diagnosis and Management

Pattern Recognition and Severity Classification

The European Respiratory Society defines the severity of restrictive lung disease based on the FEV1 percentage predicted, with moderate severity impairment representing 60-69% predicted 1
A proportional reduction in both FEV1 and FVC with a preserved ratio is the hallmark spirometric pattern suggesting restrictive impairment, and an elevated FEV1/FVC ratio of 89% is well above the lower limit of normal, definitively ruling out obstructive lung disease 2
The severity classification is as follows:

Measuring total lung capacity (TLC) is essential to confirm true restrictive lung disease, as spirometry alone cannot confirm true restriction, with a TLC below the 5th percentile of predicted confirming restriction 2, 3
Measuring diffusing capacity for carbon monoxide (DLCO) helps differentiate causes of restriction and is an important predictor of mortality in both general populations and specific disease states 1, 2
Consider parenchymal causes, such as interstitial lung diseases, and extrapulmonary causes, such as chest wall disorders and neuromuscular diseases, in the differential diagnosis of restrictive lung disease 1, 2, 3

Do not diagnose restrictive lung disease based on spirometry alone, as the FVC reduction could represent poor effort, early obstruction with air trapping, or other non-restrictive causes 2
Do not use FEV1/FVC ratio to determine severity, as both values decline together in restriction, and severity classification is based solely on FEV1 % predicted 1