What are interstitial lung diseases?
Interstitial lung disease, or ILD, is a common term that includes more than 180 chronic lung disorders, which may be:

chronic
nonmalignant (non-cancerous)
noninfectious
Interstitial lung diseases are named after the tissue between the air sacs of the lungs called the interstitium – the tissue affected by fibrosis (scarring).

Interstitial lung diseases may also be called interstitial pulmonary fibrosis or pulmonary fibrosis.

The symptoms and course of these diseases may vary from person to person, but the common link between the many forms of ILD is that they all begin with an inflammation.

bronchiolitis – inflammation that involves the bronchioles (small airways)
alveolitis – inflammation that involves the alveoli (air sacs)
vasculitis – inflammation that involves the small blood vessels (capillaries)
More than 80 percent of interstitial lung diseases are diagnosed as pneumoconiosis, a drug-induced disease, or hypersensitivity pneumonitis. The other types are:

sarcoidosis
idiopathic pulmonary fibrosis
bronchiolitis obliterans
histiocytosis X
chronic eosinophilic pneumonia
collagen vascular disease
granulomatous vasculitis
Goodpasture’s syndrome
pulmonary alveolar proteinosis
How does interstitial lung disease occur?
In interstitial lung disease, the lung is affected in three ways:

Lung tissue is damaged in some known or unknown way.
The walls of the air sacs in the lungs become inflamed.
Scarring (fibrosis) begins in the interstitium.
Fibrosis results in permanent loss of that tissue’s ability to breathe and carry oxygen. Air sacs, as well as the lung tissue between and surrounding the air sacs, and the lung capillaries, are destroyed by the formation of scar tissue.

The diseases may run a gradual course or a rapid course. People with ILD may notice variation in symptoms – from very mild, to moderate, to very severe. The condition may remain the same for long periods of time or it may change quickly. The course of ILDs is unpredictable. If they progress, the lung tissue thickens and becomes stiff. The work of breathing then becomes more difficult and demanding. Some of the diseases improve with medication if treated when inflammation occurs. Some people may need oxygen therapy as part of their treatment.

What are the symptoms of interstitial lung diseases?
The following are the most common symptoms for interstitial lung diseases. However, each individual may experience symptoms differently. Symptoms may include:

shortness of breath, especially with exertion
fatigue and weakness
loss of appetite
loss of weight
dry cough that does not produce phlegm
discomfort in chest
labored breathing
hemorrhage in lungs
The symptoms of interstitial lung diseases may resemble other lung conditions or medical problems. Consult your physician for a diagnosis.

What causes interstitial lung diseases?
The cause of interstitial lung disease is not known, however, a major contributing factor is thought to be inhaling environmental pollutants. Other contributing factors include:

sarcoidosis
certain drugs or medications
radiation
connective tissue or collagen diseases
family history
How are interstitial lungs diseases diagnosed?
In addition to a complete medical history and physical examination, the physician may also request the following tests:

pulmonary function tests – diagnostic tests that help to measure the lungs’ ability to exchange oxygen and carbon dioxide appropriately. The tests are usually performed with special machines that the person must breathe into.
spirometry – a spirometer is a device used by your physician that assesses lung function. Spirometry, the evaluation of lung function with a spirometer, is one of the simplest, most common pulmonary function tests and may be necessary for any/all of the following reasons:
to determine how well the lungs receive, hold, and utilize air
to monitor a lung disease
to monitor the effectiveness of treatment
to determine the severity of a lung disease
to determine whether the lung disease is restrictive (decreased airflow) or obstructive (disruption of airflow)
peak flow monitoring (PFM) – a device used to measure the fastest speed in which a person can blow air out of the lungs. During an asthma or other respiratory flare up, the large airways in the lungs slowly begin to narrow. This will slow the speed of air leaving the lungs and can be measured by a PFM. This measurement is very important in evaluating how well or how poorly the disease is being controlled.
chest x-rays – a diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
blood tests – to analyze the amount of carbon dioxide oxygen in the blood.
computed tomography scan (Also called a CT or CAT scan.) – a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays.
bronchoscopy – the examination of the bronchi (the main airways of the lungs) using a flexible tube (bronchoscope). Bronchoscopy helps to evaluate and diagnose lung problems, assess blockages, obtain samples of tissue and/or fluid, and/or to help remove a foreign body.
bronchoalveolar lavage – to remove cells from lower respiratory tract to help identify inflammation and exclude certain causes.
lung biopsy – to remove tissue from the lung for examination in the pathology laboratory.
Treatment for interstitial lung diseases:
Specific treatment will be determined by your physician based on:

your age, overall health, and medical history
extent of the disease
your tolerance for specific medications, procedures, or therapies
expectations for the course of the disease
your opinion or preference
Treatments may include:

oral medications, including corticosteroids
influenza vaccine
pneumococcal pneumonia vaccine
oxygen supplementation from portable containers
lung transplantation
References :
http://medicalcenter.osu.edu/patientcare/healthinformation/diseasesandconditions/respiratory/lung/interstitiallung/