What is IPF?

What is idiopathic pulmonary fibrosis, or IPF?

According to the National Institutes of Health (NIH), IPF is a condition in which over a period of time the lung tissue becomes thickened, stiff, and scarred (1). The development of the scar tissue is called fibrosis. As the lung tissue becomes scarred and thicker, the lungs lose their ability to transfer oxygen into the bloodstream. As a result, the brain and other organs don't get the oxygen they need. In some cases, doctors can determine the cause of the fibrosis, but in most cases, there is not a known cause. When there is no known etiology for the fibrosis (and certain pathologic criteria are met) the disease is called idiopathic pulmonary fibrosis or IPF. IPF affects approximately 200,000 Americans and an estimated 40,000 Americans pass away from IPF each year (1).

How is IPF Related to Interstitial Lung Disease?

There are more than 100 related diseases of the lung known as interstitial lung diseases (ILD). ILD can also be referred to as diffuse parencyhmal lung diseases (DPLD). These diseases can often have similar characteristics to IPF and most result in lung scarring. Further, IPF belongs to a subgroup of ILD called idiopathic interstitial pneumonias (IIP). IIP is further broken down into a number of pathological subtypes. The pathological pattern most commonly seen in IPF is referred to as usual interstitial pneumonia (UIP). There are a number of other subtypes of IIP. Two of the more common subtypes are nonspecific interstitial pneumonia (NSIP) and acute interstitial pneumonia (AIP).

Although this ‘alphabet’ soup is rather confusing and complicated, it is important for doctors to differentiate the cause and pattern of fibrotic disease, since standards of care and prognosis can vary. IPF is the most common of the all ILD and IIP. One recent study estimated the prevalence of all interstitial lung diseases in the United States at about 500,000 (11).

What causes IPF?

The origin (e.g. epidemiology) and development (e.g. pathogenesis) of IPF is still not completely understood. The current thinking is that there is an abnormal fibrotic and inflammatory response to microscopic injury which ultimately results in pathological scarring. There are also epidemiological and genetic factors that may contribute to the development of IPF, and as these are more clearly defined, the disease process should be better understood. Ultimately, this will lead to new pathways to treat the disease.

Epidemiological Factors: There are certain environmental or occupational exposures that seem to be prevalent in the medical histories of patients diagnosed with the disease, and as a result doctors may cite these exposures as contributing factors to a diagnosis of IPF. (If there is a clear causal relationship, which is uncommon, then the disease would no longer be considered IPF). These exposures may include the following:

  • Cigarette smoking
  • Prolonged exposure to occupational or environmental contaminants or dusts (inorganic dusts such as asbestos, silica, beryllium and hard metal dusts; organic dusts such as such as bacteria and animal proteins)
  • Viral or bacterial lung infections
  • Certain medicines such as antibiotics (Nitrofurantoin, Sulfasalazine), antiarrythmics (Amiodarone, Propranolol), anticonvulsants (Phenytoin), chemotherapeutic agents (Methotrexate, Bleomycin, Oxaliplatin, Erbital) and therapeutic radiation.
  • Acid reflux disease (GERD)

In addition, IPF may be associated with upper respiratory infections such as pneumonia and tuberculosis. The specific connection between IPF and these diseases remains largely unknown.

Interstitial lung diseases (ILD) have also been associated with connective tissue diseases including rheumatoid arthritis, scleroderma, lupus, and sarcoidosis.

Genetics and IPF: There is a growing body of clinical evidence suggesting that a family of genes may predispose certain patients to IPF. In fact 10-15% of cases are considered to be familial, which is highly suggestive of a genetic predisposition. Recent studies have found a mutation in the SP-C protein that exists in families with a history of more than 2 cases of IPF.(8) Another recent study suggested that the presence of specific genes may predict which IPF patients will have a more severe, rapidly progressing form of the disease. (5). Yet another recent study showed that shortened telomeres (which protect the fragile ends of chromosomes, and protect the end of the chromosome from deterioration) may be the cause of PF in certain patients as they grow older (6, 6a).

There is limited availability of genetic testing to identify genes that may contribute to IPF. In the absence of published findings, specifically identifying a gene or genes that are markers for IPF, patients should exercise great caution, and discuss with their physician, the benefits and risks of genetic testing.