Overview of Idiopathic Interstitial Pneumonias

Symptoms and signs of idiopathic interstitial pneumonias are usually nonspecific. Cough and dyspnea on exertion are typical, with variable onset and progression. Common signs include tachypnea, reduced chest expansion, bibasilar end-inspiratory dry crackles, and digital clubbing. Systemic rheumatic diseases such as idiopathic inflammatory myopathies, antineutrophilic cytoplasmic autoantibody (ANCA)-associated vasculitis, and rheumatoid arthritis have symptoms (eg, fevers, weight loss, malaise, myalgia, and arthralgia) that may be associated findings for most subtypes of idiopathic interstitial pneumonias.

• High-resolution CT (HRCT)

• Pulmonary function tests

• Laboratory tests

• Sometimes lung biopsy

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:

• Symptom duration

• Signs or symptoms of an underlying autoimmune disorder

• Family history of lung disease, especially lung fibrosis

• History of tobacco use (because some diseases occur mostly among people who smoke or formerly smoked)

• Current and prior prescription and illicit drug use

• Detailed review of home and work environments, including those of family members

A chronologic listing of the patient's 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 radiograph is typically abnormal, but findings are not specific enough to differentiate between the various subtypes.

Pulmonary function tests are often performed to estimate the severity of physiologic impairment, but do not help differentiate between the various subtypes. Typical results are restrictive physiology, with reduced lung volumes and diffusing 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 must be performed. 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 systemic rheumatic disease, vasculitis, or environmental exposure. Such tests may include antinuclear antibodies, rheumatoid factor, and other more specific serologic tests for systemic rheumatic diseases (eg, anti-cyclic citrullinated peptide [CCP], ribonucleoprotein [RNP], anti-Ro [SSA], anti-La [SSB], scleroderma antibody [Scl70], anti-Jo-1 antibody, myositis antibody panel).

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 interstitial idiopathic pneumonias. Bronchoalveolar lavage helps narrow the differential diagnosis in some patients and can exclude other processes, such as infection. The usefulness of this procedure in the initial clinical assessment and follow-up of most patients with these diseases has not been established.

Cryobiopsy, a technique that quickly freezes the lung tissue immediately prior to removal, is 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. Transbronchial cryobiopsy can be considered as an alternative to surgical lung biopsy in centers with experience performing it and interpreting its results.

Surgical lung biopsy is needed to confirm the diagnosis when the history and HRCT are nondiagnostic. The decision to pursue surgical lung biopsy should be done with multidisciplinary discussion. Biopsy of multiple sites with video-assisted thoracoscopic surgery (VATS) procedure is preferred.

• Varies by disorder

• Sometimes antifibrotics or glucocorticoids

• Rarely, lung transplantation

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. Supportive care is needed in many patients, such as supplemental oxygen (often home-based) and pulmonary rehabilitation; both are important adjunct therapies that relieve symptoms and improve quality of life. Coordination of care among clinicians of multiple specialties may sometimes be needed to treat the underlying disorder and, in advanced cases, sequelae of the disease (eg, cardiology if there is pulmonary hypertension).

Antifibrotics (pirfenidone, nintedanib) are typically recommended for Antifibrotics (pirfenidone, nintedanib) are typically recommended foridiopathic pulmonary fibrosis and can be considered in progressive forms of other types of pulmonary fibrosis. These medications slow the decline in lung function and disease progression.

Glucocorticoids are typically recommended for cryptogenic organizing pneumonia, lymphoid interstitial pneumonia, and nonspecific interstitial pneumonia but not for idiopathic pulmonary fibrosis. Other immunosuppressive therapies (eg, mycophenolate mofetil, azathioprine) may also be considered. . Other immunosuppressive therapies (eg, mycophenolate mofetil, azathioprine) may also be considered.

Lung transplantation may be recommended for eligible patients with end-stage disorders.