Idiopathic pulmonary fibrosis (IPF), or (formerly) fibrosing alveolitis, is a rare, progressive illness of the respiratory system, characterized by the thickening and stiffening of lung tissue, associated with the formation of scar tissue. It is a type of chronic scarring lung disease characterized by a progressive and irreversible decline in lung function. The tissue in the lungs becomes thick and stiff, which affects the tissue that surrounds the air sacs in the lungs. Symptoms typically include gradual onset of shortness of breath and a dry cough. Other changes may include feeling tired, and abnormally large and dome shaped finger and toenails (nail clubbing). Complications may include pulmonary hypertension, heart failure, pneumonia or pulmonary embolism.The cause is unknown, hence the term idiopathic. Risk factors include cigarette smoking, acid reflux disease (GERD),  certain viral infections, and genetic predisposition. The underlying mechanism involves scarring of the lungs. Diagnosis requires ruling out other potential causes. It may be supported by a HRCT scan or lung biopsy which show usual interstitial pneumonia (UIP). It is a type of interstitial lung disease (ILD).People often benefit from pulmonary rehabilitation and supplemental oxygen. Certain medications like pirfenidone (Esbriet) or nintedanib (Ofev) may slow the progression of the disease. Lung transplantation may also be an option.About 5 million people are affected globally. The disease newly occurs in about 12 per 100,000 people per year. Those in their 60s and 70s are most commonly affected. Males are affected more often than females. Average life expectancy following diagnosis is about four years.
A modified ILD-GAP Index has been developed for application across ILD subtypes to provide disease-specific survival estimates. In IPF patients, the overall mortality at 5 years rate is high but the annual rate of all-cause mortality in patients with mild to moderate lung impairment is relatively low. This is the reason  why change in lung function (FVC) is usually measured in 1-year clinical trials of IPF treatments rather than survival.In addition to clinical and physiological parameters to predict how rapidly patients with IPF might progress, genetic and molecular features are also associated with IPF mortality. For example, it has been shown that IPF patients who have a specific genotype in the mucin MUC5B gene polymorphism (see above) experience slower decline in FVC and significantly improved survival. Even if such data are interesting from a scientific point of view, the application in the clinical routine of a prognostic model based on specific genotypes is still not possible. Epidemiology
Although rare, IPF is the most common form of IIP. The prevalence of IPF has been estimated between 14.0 and 42.7 per 100,000 persons based on a USA analysis of healthcare claims data, with variation depending on the case definitions used in this analyses. IPF is more common in men than in women and is usually diagnosed in people over 50 years of age.The incidence of IPF is difficult to determine as uniform diagnostic criteria have not been applied consistently.