Restrictive lung diseases

Restrictive lung diseases are a category of respiratory disease characterised by a loss of lung compliance,[1] causing incomplete lung expansion and increased lung stiffness.
Pathophysiology
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 the FEV1 and FVC are reduced so the FEV1/FVC ratio is normal or even increased in contrast to obstructive lung disease where this ratio is reduced. The values for residual volume and total lung capacity are generally decreased in restrictive lung disease[2].

One definition requires a total lung capacity which is 80% or less of the expected value.[3]


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
•Asbestosis caused by long-term exposure to asbestos dust.
•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). Examples are:

•Idiopathic pulmonary fibrosis
•Idiopathic interstitial pneumonia, of which there are several types
•Sarcoidosis
•Eosinophilic pneumonia
•Lymphangioleiomyomatosis
•Pulmonary Langerhan’s cell histiocytosis
•Pulmonary alveolar proteinosis
Conditions specifically affecting the interstitium are called interstitial lung diseases.


Extrinsic
Quadriplegia can be a cause of restrictive lung disease.