What is Idiopathic Pulmonary Fibrosis (IPF)?
Idiopathic pulmonary fibrosis (IPF) is a general term for scarring (fibrosis) in the lung (pulmonary) and of an unknown cause (idiopathic). The term usually means that the scarring process is an active, ongoing process.
Frequency: IPF is a progression fibrotic (scar-forming) disease of the lung that affects about 13 to 20 individuals per 100,000 population, which is 25,000 to 50,000 individuals in the United States and more than 250,000 worldwide. IPF is slightly more common among men than women. The disorder can occur at all ages, usually between the ages of 50 and 80 years.
Causes: The cause of IPF is usually not known, which is reflected by the name "idiopathic" meaning "unknown". There are some known causes of pulmonary fibrosis such as certain type of medications, radiation treatment, and hazardous dust exposures. There are also several known general disorders associated with pulmonary fibrosis such as scleroderma and rheumatoid arthritis.
Symptoms: Shortness of breath is the most common symptom. This symptom is minimal at first and often not noticeable. The shortness of breath gradually worsens over months to years, and eventually becomes the most severe symptom. Cough may occur in some individuals although the cough is usually intermittent. Phlegm is unusual except in smokers. Wheezing and coughing blood are rare.
Physical examination: "Crackles" may be heard through the stethoscope. Crackles are a crackling sound or a Velcro-like sound heard. For IPF, this sound usually indicates scarring in the lung. These crackles are heard because the scarring near the airways makes hundreds of small "popping" sounds through the stethoscope as the airways open during inspiration.
Chest x-ray and chest CT: The chest x-ray shows small linear shadows, 1 millimeter to 3 millimeters, seen at the base of each lung. Sometimes, "honeycombing" is seen at the lung bases, which is a cystic pattern that has the appearance of a bee's honeycomb. These radiographic findings are very suggestive of IPF. The "high-resolution" chest CT (computed tomography) scan (HRCT or CAT scan) is the most important x-ray test for confirmation of IPF. If this study shows "honeycombing", the diagnosis of pulmonary fibrosis is established. This pattern of pulmonary fibrosis usually represents IPF.
Pulmonary Function Tests: Pulmonary function tests are obtained to confirm the pattern consistent with pulmonary fibrosis and determine severity of the process. These tests are performed in a hospital or clinic laboratory. They take 30 minutes to 1 hour and consists of blowing into a tube, sometimes performing a test in an enclosed "body box", and holding the breath for about 10 seconds. There are three important tests.
The first test is the vital capacity, which measures the amount of air in the lungs that can be expelled during a forced expiration and is referred to as the forced vital capacity (FVC). The amount of air is generally 3 to 4 liters. Fibrosis of the lung decreases the vital capacity.
The second test is FEV1, which means forced expired volume in one second. This is the amount of volume expired in one second. A decrease in the ratio of FEV1 to the FVC means airflow obstruction that may occur in asthma or emphysema. There is no airflow obstruction with pulmonary fibrosis so the FEV1/FVC ratio is normal or may even be increased.
The third test is very important for IPF. This is called diffusion or diffusing capacity. This measures the ability of oxygen to diffuse into the blood. Generally, this happens instantaneously during breathing because there is only one cell lining between the air and the blood. With IPF, there are many cells and sometimes complete scarring of this area of exchange so that the oxygen partially diffuses into the blood or in some areas does not diffuse into the blood. Therefore, a decreased diffusing capacity indicates severity of the scarring.
This is the most sensitive of the three tests for pulmonary fibrosis and may be moderate to severely decreased even though the vital capacity is normal or slightly decreased. The test is measured in "percent predicted". Mild reduction is from 60% to 80% predicted, moderate reduction is from 40% to 59%, while values less than 40% predicted indicate severe impairment from the scarring.
What is Usual Interstitial Pneumonia (UIP)?
Usual Interstitial Pneumonia (UIP) is a specific term used by lung pathologists as one of several interstitial pneumonias (the interstitium is a word used for the cellular support structures of the lung). UIP is the most common type of interstitial pneumonia.
IPF is often used as synonymous with UIP because UIP is the most common cellular pattern, and its cause is usually not known. The designation "IPF/UIP" is also commonly used to describe this process of progressive pulmonary fibrosis.
There are several interstitial pneumonias, in the 1960's, Professor Liebow used the term "usual" to describe the usual pattern seen for the interstitial pneumonias. This term continues to be used today or the terms "IPF" or "IPF/UIP" are utilized.
The term "cryptogenic fibrosing alveolitis" is synonymous with UIP. "Cryptogenic" means an unknown cause. "Fibrosing" means progressive or ongoing scar formation of the interstitium and alveoli. "Alveolitis" means inflammation of the alveoli, which are small spherical oxygen exchange units in the lung.
Microscopic Findings: The microscopic findings of UIP show three findings in the lung tissue: (1) Areas of normal lung, (2) Areas of inflammation, and (3) Areas of end-stage, scared, and non-functioning cystic lung with the appearance of a honeycomb. "Architectural derangement" of the lung is seen. "Fibroblastic foci" seen in the areas of inflamed lung establish the diagnosis of UIP. These foci are scar-forming cells called fibroblasts.
These cells are rarely seen in healthy lungs, and their presence in a group (foci) indicates the ongoing scarring process of UIP. Sometimes the area of inflammation has the appearance of cellular organization called BOOP (Bronchiolitis Obliterans Organizing Pneumonia). This BOOP process is not the primary disorder but is secondary to the underlying primary disorder of UIP.
The Process: The UIP process is one of gradual replacement of the lung tissue with scar and fibrosis. The cause of this process is not known. The appearance of the "fibroblastic foci" suggests that these fibroblast cells, which are usually beneficial by producing scar to heal an injury, malfunction and continue to live producing scar instead of the normal termination response. Extensive research is being conducted to clarify this reaction so that medications can be developed to stop this abnormal process.
Causes: The cause of UIP is usually not known, and therefore often used interchangeably with IPF (IPF/UIP). There are some known causes of UIP such as certain type of medications, radiation treatment, and hazardous dust exposures. There are also several known general disorders associated with pulmonary fibrosis such as scleroderma and rheumatoid arthritis.
Is UIP Contagious?
No, IPF/UIP is not contagious
Is UIP Inherited?
In rare situations, UIP may occur in several family members and passed on from one generation to the next. The type of inheritance is currently being investigated through genetic testing.