Interstitial Lung Disease
Interstitial lung disease is also referred to as diffuse parenchymal lung disease and it refers to a number of lung conditions that affect the interstitium of the lung tissue.  It can involve the epithelium of the alveoli, the basement membrane, the perivascular tissues, the capillary endothelium and the perilymphatic tissues. Interstitial lung diseases are different from obstructive airway disease or COPD. 
Interstitial lung disease is characterized by a great deal of fibrosis, which is often a later manifestation of the disease.  The actual cause of this fibrosis is idiopathic, leading to the diagnosis of “idiopathic pulmonary fibrosis”.
Interstitial lung disease is classified according to the reasons behind the disease.  They include inhaled substances, often in the workplace, such as silicosis, berylliosis and asbestosis.   Organic inhaled substances lead to hypersensitivity pneumonitis.  Drugs can cause interstitial lung disease, particularly, antibiotics, antiarrhythmic medications and chemotherapeutic medications.  Connective tissue diseases can lead to interstitial lung disease, especially systemic sclerosis, systemic lupus erythematosis, rheumatoid arthritis and dermatomyositis.  Infectious causes of interstitial lung disease include a bout with atypical pneumonia, tuberculosis and pneumocystis pneumonia.  Those that are considered idiopathic causes include idiopathic pulmonary fibrosis, sarcoidosis and Hamman-Rich Syndrome.  There is, in fact, a malignancy that is related to interstitial lung disease and that is lymphangitic carcinomatosis. 
Diagnosis
The diagnosis is often seen by XRAY, where reticular markings are seen on the film.  The rest of the investigation depends on the signs and symptoms of the disease, pulmonary function testing and CT scan of the thorax.  A lung biopsy can be used as a last resort to define the nature of the lung tissue.  Bronchoscopy with biopsy is a simple method of getting a sampling of lung tissue.  Measurement of oxygen levels in the blood at rest or after exertion can help diagnose the disease.  Blood tests to check for the presence of connective tissue diseases can be helpful in certain situation. 
Symptoms
Those with interstitial lung disease often have clubbing or an enlargement of the base of the fingernails, decreased tolerance for physical activity, cyanosis of the skin or lips, dry, frequent cough, breathing which is too rapid and shortness of breath while active or at rest. 
Treatment of Interstitial Lung Disease
It is important to understand that interstitial lung disease is not considered a single disease but involves a range of pathological processes.  This means that the treatment is different for each type of disease that falls under the umbrella of interstitial lung disease.  For example, if it is found to be due to an occupational exposure, the individual must get out of that environment.  If a medication or drug is found to be the cause, it must be discontinued.  Other etiologies of interstitial lung disease respond very well to the giving of corticosteroids such as prednisone or prednisolone.  Patients low in oxygen are treated with supplemental oxygen through a nasal cannula or oral mask, depending on how severe the low oxygen.
Interstitial lung disease seems to be related to oxidative stress in the lungs.  This causes an infiltration of inflammatory cells, which furthers inflammation.  The use of the antioxidant glutathione seems to help balance the redox status of the lungs and has the potential to be an effective treatment for interstitial lung disease.