Interstitial lung disease (ISLD) is a multifaceted disorder. It is characterized by interstitial infiltrative and sometimes fibrotic lesions on plain chest x-ray. Patients often complain of shortness of breath, persistent dry cough or simple fatigue. Many patients are brought to the attention of physicians because of an unsuspected abnormality seen on their chest x-ray.
The differential diagnosis of interstitial disease includes many connective tissue diseases, granulomatous disorders, neoplasms, drug induced disorders, organic dust disease, inherited disorders, poison induced lung injury, infections, occupational induced lung disease, and idiopathic pulmonary fibrosis.
A fibrotic reaction may present after pneumonitis but will not demonstrate progression either by chest x-ray or pulmonary function testing criteria in 15-20% of patients evaluated for interstitial lung disease.
We believe that all patients with interstitial lung disease should receive a basic evaluation that includes the following:
- All patients should have laboratories done for collagen vascular diseases.
- Careful history should be done for pneumoconiosis and drug induced disease.
- We try to establish disease progression:
- Obtain chest x-rays, two or more years apart to look for stability or advancing of the pulmonary markings.
- Pulmonary function changes that are significant include a decrease in the vital capacity of 10% or more, decrease in the DLCO by 20% or more, or an elevation in the alveolar to arterial oxygen gradient by 5 mm of mercury or more.
- Appropriate patients should undergo fiberoptic bronchoscopy to rule out granulomatous disease, neoplasm, infection, pulmonary alveolar proteinosis, histiocytosis X. These disorders are treatable and patients may have an excellent prognosis.
In patients with irreversible forms of interstitial lung disease, the prognosis is quite grim. We have experienced similar results in survival that have been reported in the literature for patients with idiopathic pulmonary fibrosis. It has been largely reported that the average duration of survival in these patients is in the 4-5 year range after diagnosis. There are subsets of patients with idiopathic pulmonary fibrosis that have an excellent response to treatment and their survival is prolonged.
The treatment of idiopathic pulmonary fibrosis can be very frustrating. Of the options available, we favor corticosteroid therapy, sometimes combined with cyclophosphamide. 10-20% of patients will have a measurable response to corticosteroid therapy alone. We look at the pulmonary function changes as described above to determine if lung disease has stabilized or if the patient has actually regained function. Azathioprine has been used with some success in the literature but we have not found it to be that useful in clinical practice.