Using an evidence-based approach to diagnose IPF
Honeycomb appearance of the lungs caused by idiopathic pulmonary fibrosis.
Idiopathic pulmonary fibrosis (IPF) is the most common form of interstitial lung disease (ILD) in the subgroup of ILDs called idiopathic interstitial pneumonia (IIP).1 IPF is defined by a combination of the following 2 features: 1) an idiopathic clinical circumstance (ie, the absence of exposures or diseases known to cause pulmonary fibrosis) and 2) a pattern of usual interstitial pneumonia (UIP) on high-resolution computed tomography (HRCT) or surgical lung biopsy.1 "Idiopathic" by name, IPF requires the exclusion of all known causes of ILD in the diagnostic workup. This is a critical step, because a number of respiratory illnesses can mimic the clinical presentation of IPF,2 including connective tissue disease (CTD)-related pulmonary fibrosis, hypersensitivity pneumonia, or asbestosis.1,2 Clinical features of IPF include chronic exertional dyspnea, dry cough, bibasilar inspiratory crackles ("Velcro crackles"), and finger clubbing.1,3
Although IPF has no known cause, risk factors include cigarette smoking and several environmental exposures.1 For example, various dusts (eg, metal, agricultural) have been linked to IPF. Additionally, comorbidities such as gastroesophageal reflux disease (GERD) and diabetes have been described as risk factors for IPF.1 IPF is believed to result from injury to the alveolar epithelium. The currently accepted theory of IPF pathogenesis holds that aberrant wound healing leads to progressive fibrosis and architectural distortion of the lung.1,4
IPF typically affects adults aged ≥50 years and increases in incidence with advancing age, often presenting when patients are in their 60s or 70s.1 A recent study of Medicare patients aged ≥65 years revealed a stable incidence of IPF from 2001 to 2011, with an estimated 93.7 cases per 100,000 person-years.5 Over the same time, the cumulative prevalence steadily increased from 202.2 cases per 100,000 person-years to 494.5 cases per 100,000 person-years. There was a higher incidence of IPF (and shorter survival time after diagnosis) in male patients.5 With the US population increasing in age, the number of patients with IPF is expected to increase.
Mostly because IPF is not as common as certain other respiratory illnesses, >50% of IPF patients are initially misdiagnosed, and many patients are evaluated by more than 3 physicians before being accurately diagnosed with IPF.2,6 Consequently, by the time a diagnosis is confirmed, many patients will have already endured irreversible damage in the lungs and experienced profound impairments in quality of life.1,7
IPF has an unpredictable and variable natural history, but results of several studies estimate median survival at only 3 years from the time of diagnosis.1 Management options for patients with IPF include supplemental oxygen as needed to maintain normoxia, pulmonary rehabilitation, and possibly pharmacologic treatment aimed at slowing disease progression. There is no cure for IPF. Lung transplantation is an option for a minority of patients.1 For optimal health outcomes, an early and accurate diagnosis is necessary. Therefore, it is imperative that the index of suspicion of IPF be raised among primary care physicians (PCPs) to enable quick recognition of IPF and exclusion of other causes of pulmonary fibrosis.