Interstitial Lung Disease (Interstitial Pneumonia)

Interstitial lung disease includes a group of diseases that have thickening of the supporting tissues between the air sacs of the lungs as the common factor.

• Interstitial lung disease refers to inflammation in the interstitial tissue of the lungs, the spaces that surround and separate the air sacs.
• Interstitial lung disease is believed to be caused by an exaggerated or misdirected immune response to various stimuli.
• Some of the factors that can precipitate the inflammation in interstitial lung disease include certain medications, infections, toxins, and some chronic conditions.
• If the inflammation of the interstitial tissue leads to scarring over time, the term interstitial fibrosis is used to describe the condition. If the cause is not known, the condition is termed idiopathic pulmonary fibrosis.
• Symptoms of interstitial lung disease include:
  • shortness of breath, and
  • a dry cough.
• Treatment depends on the underlying cause of the inflammation.
• Corticosteroid drugs and immune-suppressing drugs may be used in the management of interstitial lung disease.
• Smoking cessation is essential for people with interstitial lung disease.

Sometimes the term "interstitial pneumonia" is used for certain forms of interstitial lung disease.

Interstitial lung disease is a term used to refer to a particular type of inflammation of the interstitium of the lungs. The interstitium is the tissue that surrounds and separates the tiny air sacs (alveolae) in the lungs. Interstitial lung disease involves an inflammation of this supportive tissue between the air sacs rather than inflammation in the air sacs themselves. Interstitial inflammation is typically a diffuse process that occurs all over the lungs and is not confined to one location.

Sometimes the term "interstitial pneumonia" is used for certain forms of interstitial lung disease. Technically, however, the term "pneumonia" refers to inflammation of the lung tissue that is usually associated with infection. Because interstitial lung disease has a number of causes (most of which are not related to infection), the term "interstitial pneumonitis" is occasionally used to refer to the inflammation that occurs in the absence of true infection.

Interstitial lung disease is felt to be caused by a misdirected immune or healing reaction to a number of factors, including:

• infections of the lungs;
• toxins in the environment (such as asbestos, silica dust);
• certain medications (particularly some drugs used as chemotherapy for cancers);
• radiation therapy to the chest; and
• chronic autoimmune diseases: connective tissue diseases such as lupus, scleroderma, and rheumatoid arthritis

Sometimes, the process of inflammation and scarring of the interstitial tissues of the lungs develops in the absence of a known cause. When no cause can be identified, this is referred to as idiopathic (unknown cause) interstitial lung disease or idiopathic pulmonary fibrosis. Depending upon the location, severity, and pattern of lung involvement, the idiopathic interstitial lung diseases have been further subdivided into categories. Examples of different types of idiopathic interstitial lung disease include:

• usual interstitial pneumonitis (UIP),
• bronchiolitis obliterans with organizing pneumonia (BOOP),
• lymphocytic interstitial pneumonitis (LIP), and
• desquamative interstitial pneumonitis (DIP).

Decreased lung function is the result of the inflammation present in the supporting interstitial tissues, which leads to scarring and thickening. This is because the thickened and stiff tissues cannot breathe as effectively as healthy lung tissue. Symptoms, therefore, are related to the reduced efficiency of breathing and corresponding reduced levels of oxygen in the blood.

The symptoms depend to a certain extent upon the exact cause of the condition, but the shortness of breath and a dry cough are the most common symptoms. In most cases, these symptoms develop gradually. Signs of chronically reduced oxygen levels in the blood include clubbing (a painless enlargement of the fingertips) and an enlarged heart.

Interstitial lung disease can lead to serious long-term complications.

• Pulmonary hypertension, a type of high blood pressure that affects the arteries within the lungs, may develop.
• Ultimately, right-sided (the side of the heart that pumps blood back to the lungs to receive oxygen) heart failure may result (known as cor pulmonale).
• Respiratory failure is a potentially fatal long-term complication of interstitial lung disease.

Interstitial lung disease cannot be diagnosed simply on the basis of a medical history and physical examination. In most cases, a number of diagnostic tests must be used. The symptoms of interstitial lung disease overlap with those of many other conditions, including cardiovascular diseases.

• Blood tests may help provide direction in the initial stage of diagnosis and rule out other conditions that may have similar symptoms. Measurement of the oxygen level in the arterial blood may also be performed.
• Imaging studies, such as chest X-rays and CT scans are often the first diagnostic step and may also help rule out other conditions that may cause similar symptoms.
• Pulmonary function tests (PFTs) are noninvasive tests that measure the function of the lungs. The test involves blowing into a tube that is part of an instrument called a spirometer. This can measure the volume of the lungs as well as the air flow into and out of the lungs.
• Biopsies or washings may be taken of the lungs and airways during bronchoscopy (examination of the airways with a viewing tube). The removed tissue samples are then examined by a pathologist to establish the diagnosis. In certain cases, open surgical biopsy of the lung may be required to obtain an adequate tissue sample for diagnosis.

The choice of treatment depends upon a number of factors including the cause of the interstitial lung disease and the overall health status of the patient.

• Most commonly, corticosteroid drugs are given in an attempt to reduce inflammation.
• Sometimes, immune-suppressing drugs, such as azathioprine Imuran) or cyclophosphamide (Cytoxan) are also given, either in combination with steroids or following a course of steroid treatment.
• Some patients with interstitial lung disease benefit from oxygen therapy and/or respiratory therapy (pulmonary rehabilitation) to improve daily functioning.
• Smoking cessation is critical for those with interstitial lung disease.
• Finally, in severe cases, lung transplantation may be considered in certain patients.