Idiopathic pulmonary fibrosis is a progressive lung disease of unknown etiology characterized by thickening of alveolar walls and the presence of large mononuclear cells in the alveolar space. Although idiopathic pulmonary fibrosis is believed to be underdiagnosed, the prevalence in the United States has been estimated to be 29 per 100,000 men and 26 per 100,000 women. A recent review by Chan-Yeung and Müller provides diagnostic and treatment guidelines.
The typical patient with idiopathic pulmonary fibrosis is 40 to 70 years of age and presents with a one- to three-year history of nonproductive cough and increasing breathlessness. Physical examination usually reveals bilateral basilar crackles and clubbed fingers. Approximately one third of patients have an autoimmune condition, such as polyarthritis. Although chest radiographs typically show a diffuse reticular pattern predominately in the lower zones, in up to 16 percent of patients the chest radiograph may appear normal. High-resolution computed tomographic (CT) scan shows linear opacities and honeycombing with areas of ground-glass attenuation. Tests of lung function show restrictive results such as low lung volumes and impaired gas transfer.
The diagnosis is based on exclusion of other causes of fibrosing alveolitis. A thorough occupational and environmental exposure history is particularly important. High-resolution CT scan is crucial in confirming the diagnosis. Since patients with ground-glass attenuation are more likely to respond to corticosteroids, the CT scan also guides choice of therapy. Transbronchial lung biopsy and bronchoalveolar lung lavage do not contribute directly to the diagnosis of idiopathic pulmonary fibrosis but are useful in identifying other potential diagnoses such as sarcoidosis, hypersensitivity pneumonitis, cryptogenic organizing pneumonia and malignancy. Lung biopsy using either open or transbronchial routes confirms the diagnosis; samples should be obtained from at least two sites.
The treatment of idiopathic pulmonary fibrosis is controversial and is hampered by a lack of understanding of the natural history of the disease. Only 10 to 15 percent of patients improve with corticosteroid therapy, and 26 percent of patients develop serious complications from the steroid therapy. Indicators of good response to steroid therapy include young age, female sex, ground-glass lesions on CT scan and active inflammation on lung biopsy samples. Azathioprine, cyclophosphamide and other cytotoxic drugs have been used either as second-line agents or in combination with steroids as first-line therapy. Although the general prognosis was poor, combined treatment improved three-year survival rates. Selected patients with idiopathic pulmonary fibrosis have been treated with lung transplantation.