DIAGNOSIS
IPF belongs in the general class of idiopathic interstitial pneumonias (IIPs), which are characterized by varying degrees of inflammation and fibrosis of lung interstitium.4 All subtypes of IIPs cause dyspnea and diffuse abnormalities on HRCT, and all vary from each other histologically. Table 1 outlines the key features of each.5-8
Because of its vague symptomology and the extensive workup needed to rule out other diseases, patients with IPF often have symptoms for one to two years before a diagnosis is made.1 Physical exam may reveal fine inspiratory rales in both lung bases and digital clubbing; eventual signs of pulmonary hypertension and right-sided heart failure may be appreciated.1,9
There are no specific diagnostic laboratory tests to confirm IPF; however, baseline labwork (as outlined in the case presentation) is typically ordered to rule out infection, thyroid disease, or connective tissue disease.10 Many patients are referred to a cardiologist before being seen by a pulmonologist; cardiac stress testing may be done, and an echocardiogram may be performed to rule out heart failure.
Diagnostic testing may include pulmonary function testing, HRCT of the chest, and lung biopsy.10 Tissue samples from patients with IPF reveal different stages of disease, including dense fibrosis with honeycombing, subpleural or paraseptal distribution, fibroblast foci, and normal tissue.11 Pulmonary function test results will show a restrictive pattern. Both forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) will be reduced, and the FEV1/FVC ratio preserved. Due to decreased functional lung volume, diffusing capacity of the lung for carbon monoxide (DLCO) will also be reduced.4,12
The differential is broad and includes allergic asthma, bronchitis, COPD, lung cancer, hypersensitivity pneumonitis, asbestosis, or pulmonary embolism.
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