Restrictive lung disease

Restrictive lung diseases (or restrictive ventilatory defects) are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.

Pathophysiology

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In disorders that are intrinsic to the lung parenchyma, the underlying process is usually pulmonary fibrosis (scarring of the lung). As the disease progresses, the normal lung tissue is gradually replaced by scar tissue interspersed with pockets of air. This can lead to parts of the lung having a honeycomb-like appearance.

Presentation

The main symptoms are shortness of breath and cough.

Diagnosis

In restrictive lung disease, both forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) are reduced, however, the decline in FVC is more than that of FEV1, resulting in a higher than 80% FEV1/FVC ratio. In obstructive lung disease however, FEV1 is reduced while FVC remains stable, consequentially depicting a lower FEV1/FVC ratio.

One definition requires a total lung capacity which is 80% or less of the expected value.

Causes and classification

Restrictive lung diseases may be due to specific causes which can be intrinsic to the parenchyma of the lung, or extrinsic to it.

Intrinsic

• Pneumoconiosis caused by long-term exposure to dusts, especially in mining. For example Asbestosis.
• Radiation fibrosis, usually from the radiation given for cancer treatment.
• Certain drugs such as amiodarone, bleomycin and methotrexate.
• As a consequence of another disease such as rheumatoid arthritis.
• Hypersensitivity pneumonitis due to an allergic reaction to inhaled particles.
• Acute respiratory distress syndrome (ARDS), a severe lung condition occurring in response to a critical illness or injury.
• Infant respiratory distress syndrome due to a deficiency of surfactant in the lungs of a baby born prematurely.

Many cases of restrictive lung disease are idiopathic (have no known cause). Still, there is generally pulmonary fibrosis. Examples are:

• Idiopathic pulmonary fibrosis
• Idiopathic interstitial pneumonia, of which there are several types
• Sarcoidosis
• Eosinophilic pneumonia
• Lymphangioleiomyomatosis
• Pulmonary Langerhans' cell histiocytosis
• Pulmonary alveolar proteinosis

Conditions specifically affecting the interstitium are called interstitial lung diseases.

Extrinsic

• Extrinsic asthma is also a type of restrictive lung disease.
• Nonmuscular diseases of the upper thorax such as kyphosis and chest wall deformities.
• Diseases restricting lower thoracic/abdominal volume (e.g. obesity, diaphragmatic hernia, or the presence of ascites).
• Pleural thickening.