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Idiopathic interstitial pneumonia
Last reviewed: 07.07.2025
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Idiopathic interstitial pneumonias are interstitial lung diseases of unknown etiology that share similar clinical features. They are classified into 6 histologic subtypes and are characterized by varying degrees of inflammatory response and fibrosis and are accompanied by dyspnea and typical changes in radiography. The diagnosis is established by analyzing the anamnesis, physical examination, radiographic studies, pulmonary function tests, and lung biopsy.
Six histologic subtypes of idiopathic interstitial pneumonia (IIP) have been defined, listed in decreasing order of frequency: usual interstitial pneumonia (UIP), known clinically as idiopathic pulmonary fibrosis; nonspecific interstitial pneumonia; bronchiolitis obliterans organizing pneumonia; respiratory bronchiolitis associated with interstitial lung disease (RBAILD); desquamative interstitial pneumonia; and acute interstitial pneumonia. Lymphoid interstitial pneumonia, although still sometimes considered a subtype of idiopathic interstitial pneumonia, is now thought to be part of the lymphoproliferative disorders rather than primary IBLAP. These subtypes of idiopathic interstitial pneumonia are characterized by varying degrees of interstitial inflammation and fibrosis and all result in dyspnea; diffuse changes on chest radiograph, usually in the form of increased pulmonary markings, and are characterized by inflammation and/or fibrosis on histological examination. The classification presented is due to the different clinical features of individual subtypes of idiopathic interstitial pneumonia and their different response to treatment.
[ Diagnosis of idiopathic interstitial pneumonia
Known causes of ILD should be excluded. Chest radiography, pulmonary function tests, and high-resolution CT (HRCT) are performed in all cases. The latter allows differentiation of cavity lesions from interstitial lesions, provides a more accurate assessment of the extent and location of the lesion, and is more likely to detect underlying or associated disease (eg, occult mediastinal lymphadenopathy, malignancy, and emphysema). HRCT is best performed with the patient in the prone position to reduce atelectasis of the lower lungs.
A lung biopsy is usually required to confirm the diagnosis, unless the diagnosis is made on HRCT. Bronchoscopic transbronchial biopsy may exclude IBLAR by diagnosing another disorder, but does not provide sufficient tissue to diagnose IBLAR. As a result, a diagnosis may require biopsy of multiple sites during open or VATS surgery.
Bronchoalveolar lavage may help narrow the differential diagnosis in some patients and provide information on disease progression and response to treatment. However, its usefulness in the initial clinical evaluation and follow-up in most cases of this disease has not been established.
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Treatment of idiopathic interstitial pneumonia
Treatment of idiopathic interstitial pneumonia depends on the subtype but usually includes glucocorticoids and/or cytotoxic agents, but is often ineffective. Idiopathic interstitial pneumonia has a variable prognosis. It depends on the subtype and ranges from very good to almost always fatal.