The 8 histologic subtypes of IIP, in decreasing order of frequency, are
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Idiopathic pulmonary fibrosis (identified histologically as usual interstitial pneumonia)
These subtypes are characterized by varying degrees of interstitial inflammation and fibrosis (1). All cause dyspnea; diffuse abnormalities on high-resolution CT (HRCT); and inflammation, fibrosis, or both on biopsy. The subtypes are important to distinguish, however, because they have different clinical features (see Table: Key Features of Idiopathic Interstitial Pneumonias*) and respond differently to treatment.
Key Features of Idiopathic Interstitial Pneumonias*
General reference
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1. Travis WD, Costabel U, Hansell DM, et al: An Official American Thoracic Society/European Respiratory Society Statement: Update of the International Multidisciplinary Classification of the Idiopathic Interstitial Pneumonias. Am J Respir Crit Care Med 188 (6):733–748, 2013.
Symptoms and Signs
Diagnosis
Idiopathic interstitial pneumonia should be suspected in any patient with unexplained interstitial lung disease. Clinicians, radiologists, and pathologists should exchange information to determine the diagnosis in individual patients. Potential causes (see table Causes of Interstitial Lung Disease) are assessed systematically. For maximum diagnostic yield, history should address the following criteria:
A chronologic listing of the patient's entire employment history, including specific duties and known exposures to organic and inorganic agents (see table Causes of Interstitial Lung Disease), is obtained. The degree of exposure, duration of exposure, latency of exposure, and the use of protective devices is elicited.
Chest x-ray is done and is typically abnormal, but findings are not specific enough to differentiate between the various types.
Pulmonary function tests are often done to estimate the severity of physiologic impairment, but they do not help differentiate between the various types. Typical results are restrictive physiology, with reduced lung volumes and diffusion capacity. Hypoxemia is common during exercise and may be present at rest.
HRCT, which distinguishes airspace from interstitial disease, is the most useful test and is always done. It provides assessment of the potential etiology, extent, and distribution of disease, and is more likely to detect underlying or coexisting disease (eg, occult mediastinal adenopathy, cancer, emphysema). HRCT should be done with the patient supine and prone and should include dynamic expiratory imaging to accentuate evidence of small airway involvement.
Laboratory tests are done for patients who have clinical features suggesting a connective tissue disorder, vasculitis, or environmental exposure. Such tests may include antinuclear antibodies, rheumatoid factor, and other more specific serologic tests for connective tissue diseases (eg, ribonucleoprotein [RNP], anti-Ro [SSA], anti-La [SSB], scleroderma antibody [Scl70], anti-Jo-1 antibody ).
Bronchoscopic transbronchial biopsy can help differentiate certain interstitial lung diseases, such as sarcoidosis and hypersensitivity pneumonitis, but the biopsy does not yield enough tissue to diagnose the IIPs. Bronchoalveolar lavage helps narrow the differential diagnosis in some patients and can provide information about disease progression and response to therapy. The usefulness of this procedure in the initial clinical assessment and follow-up of most patients with these diseases has not been established, however.
Cryobiopsy, a technique that quickly freezes the lung tissue immediately prior to removal, is being investigated as an aid to diagnosis of certain interstitial lung diseases. The tissue yield is higher than that of transbronchial biopsy but lower than surgical lung biopsy. Risks of the procedure include bleeding and pneumothorax. Cryobiopsy is currently under investigation and is not recommended by international guidelines; its role in diagnosis remains to be established.
Surgical lung biopsy is needed to confirm the diagnosis when the history and HRCT are nondiagnostic. Biopsy of multiple sites with a video-assisted thoracoscopic surgery (VATS) procedure is preferred.
Treatment
Treatment varies by disorder (see table Treatment and Prognosis of Idiopathic Interstitial Pneumonias). Smoking cessation is always recommended to avoid potentially accelerating disease progression and to limit respiratory comorbidities.
Corticosteroids are typically recommended for cryptogenic organizing pneumonia, lymphocytic interstitial pneumonia, and nonspecific interstitial pneumonia but not for idiopathic pulmonary fibrosis.
Lung transplantation may be recommended for selected patients with end-stage disorders.
Treatment and Prognosis of Idiopathic Interstitial Pneumonias*
Key Points
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There are 8 histologic subtypes of idiopathic interstitial pneumonia.
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Symptoms, signs, and chest x-ray findings are nonspecific.
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Diagnose IIPs initially based primarily on history and high-resolution CT (HRCT).
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When clinical evaluation and HRCT are not diagnostic, do surgical lung biopsy.
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Treatment varies by subtype.
Drugs Mentioned In This Article
| Drug Name | Select Trade |
|---|---|
mycophenolate |
CELLCEPT |
azathioprine |
IMURAN |
Pirfenidone |
ESBRIET |
nintedanib |
OFEV |
