Restrictive lung disease

Restrictive lung disease describes any condition that limits lung expansion, shrinking lung volumes. The defining physiologic finding is a reduced total lung capacity (TLC). Because both FEV1 and FVC fall together, the FEV1/FVC ratio stays normal or rises — the key spirometry contrast with obstructive disease, where the ratio falls because airflow, not volume, is the problem.

Causes divide into two groups. Intrinsic (pulmonary) causes stiffen the lung tissue itself: idiopathic pulmonary fibrosis, pneumoconioses such as silicosis and asbestosis, sarcoidosis, hypersensitivity pneumonitis, and drug- or radiation-induced fibrosis. Extrinsic (extrapulmonary) causes restrict expansion from outside the lung: chest wall deformities like severe kyphoscoliosis, obesity hypoventilation, and neuromuscular diseases such as myasthenia gravis, Guillain-Barré syndrome, and ALS that weaken the respiratory muscles.

Patients typically present with progressive exertional dyspnea and a rapid, shallow breathing pattern; fibrotic disease adds dry crackles and, over time, hypoxemia from impaired diffusion. Management targets the underlying cause — antifibrotics for pulmonary fibrosis, immunosuppression for inflammatory disease, ventilatory support for neuromuscular failure — which is why classifying the pattern correctly matters clinically.

Restrictive physiology is tested across health exams. USMLE Step 1 emphasizes the pulmonary function test pattern and the intrinsic-versus-extrinsic classification, while the NPTE and NPTE-PTA test recognizing restrictive disease during auscultation, differential diagnosis, and rehabilitation planning for pulmonary patients.