In simplest terms, pulmonary fibrosis equates with the growth of “scar” in the lung. Scarred lung can assume any one of a variety of patterns; these patterns define unique pathologic phenotypes. When scar assumes a patchy distribution and appears to emanate from the pleural surface, it is recognized as the “usual” type—otherwise known as usual interstitial pneumonia (UIP). The disease in which UIP manifests without cause or trigger is called idiopathic pulmonary fibrosis (IPF). IPF is, therefore, a type of pulmonary fibrosis (also known as interstitial lung disease [ILD]). IPF is recognized by a unique compilation of clinical, radiographic, and pathologic features. IPF causes breathlessness, disability due to respiratory insufficiency and, in most instances, eventually leads to death.
While there are many causes of ILD, IPF is the most common form of ILD and certainly the most serious. IPF is characterized by an inexorable progression of interstitial pulmonary fibrosis that results in restrictive lung disease and worsening gas exchange. Death from respiratory failure is reported to ensue within 5 years of diagnosis in the majority of patients.
By definition, IPF is UIP in the absence of cause or explanation. It is equally important to remember what IPF is not. IPF is not pulmonary fibrosis from chronic aspiration, drug toxicities, environmental exposures (such as chronic hypersensitivity pneumonitis), and collagen vascular diseases, even if the pattern of fibrosis resembles UIP. Therefore, the diagnosis of IPF can only be made by excluding other possibilities. One of the major challenges in diagnosing IPF is the reasonable exclusion of other potential causes of pulmonary fibrosis. This requires a careful clinical and diagnostic evaluation; and often verges on areas of clinical uncertainty.
IPF typically comes to medical attention later in life, beginning in the sixth decade. IPF is rarely the cause of ILD in patients under the age of 40. The predominant presenting symptoms of IPF are exertional breathlessness and a dry, harassing cough. These are nonspecific complaints shared by a variety of pulmonary and cardiac diseases. In particular, exertional breathlessness is often attributed to advancing age by patients in their sixties and seventies, leading to delays in seeking medical evaluation. In addition, many patients are poorly conditioned and overweight and attribute their symptoms of breathlessness to these circumstances. In addition to nonspecific clinical symptoms, initial nonspecific radiographic findings also fail to trigger prompt medical evaluation. Fine peripheral linear radiographic opacities on plain chest radiographs, predominantly in the lower lung zones, may be interpreted as chronic and nonspecific pulmonary fibrosis, which often does not elicit an alarming response. Delay in diagnosis is therefore the norm. However, in recent years important scientific advances have improved the understanding of IPF pathogenesis; new therapeutic trials are under way and this has increased the enthusiasm for an early diagnosis of IPF.
A brief review of the evolution in our understanding of IPF ...