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Pulmonology - Interstitial Lung Disease - Fast Facts | NEJM Resident 360

The interstitial lung diseases (ILDs) are a collection of chronic lung conditions characterized by impaired gas exchange caused by abnormalities in the lung interstitium. ILDs may occur secondarily to connective tissue disease, medication, environmental or occupational exposures, infection, or cancer. A subset of these diseases occurs idiopathically, with idiopathic pulmonary fibrosis (IPF) being the most common. The approximate distribution of ILDs in the United States is depicted in the following figure:

Estimated Relative Distribution of Specific Interstitial Lung Diseases (ILDs) in the United States

(Source: Idiopathic Pulmonary Fibrosis. N Engl J Med 2018.)

Assessment

Etiology: In general, determining the underlying etiology of ILD is important to guide treatment and predict prognosis. The following common classification system is used to categorize the major subgroups of ILD and related causes:

ILD Classification Scheme

(Reproduced with permission from The Royal Australian College of General Practitioners from Troy L, Corte T. Interstitial Lung Disease in 2015: Where Are We Now?, Aust Fam Physician 2015;44(8):546–52.)

Comprehensive history: When evaluating patients for suspicions of ILD, an important first step is to determine if the disease is secondary to a known cause. All patients should be asked about:

• history of autoimmune disease: including myositis, mixed connective tissue diseases, rheumatoid arthritis, scleroderma, Sjögren syndrome, and vasculitis

• medications and therapies: including amiodarone, nitrofurantoin, isoniazid, thiazides, sulfonamides, bleomycin, methotrexate, and radiation

• occupational or avocational exposure: to organic (e.g., spores, pigeon droppings causing hypersensitivity pneumonitis) and inorganic (e.g., coal, silicon dust, asbestos causing pneumoconiosis) substances

Quantitate pulmonary symptoms: In addition to asking about potential exposures, it is important to quantitate associated pulmonary symptoms, including dyspnea, cough, fatigue, and exercise tolerance. To quantitate, ask how far or long a person can walk or climb stairs without becoming short of breath.

Physical exam: As with the history, the physical exam can help determine the potential etiology of ILD and the severity of the illness. Physical exam findings tend to reflect chronic hypoxemia. Therefore, it is important to examine for the following symptoms:

• cachexia

• resting tachypnea and accessory muscle use

• intercostal indrawing

• reduced chest wall expansion

• cyanosis

• digital clubbing

• Velcro-like crackles (can predate other clinical manifestations)

• pulmonary hypertension (in severe disease)

Dermatologic and musculoskeletal exams: Screen for possible rheumatologic conditions. Please refer to systemic sclerosis, inflammatory myopathies, rheumatoid arthritis , and undifferentiated inflammatory arthritis in the Rheumatology rotation guide).

Investigations

High-resolution computed tomography (CT) of the chest: In most cases, a high-resolution CT scan of the chest is mandatory for diagnosis. Other investigations (e.g., pulmonary function testing and 6-minute walk distance) can be used to monitor disease progression during follow-up.

The following investigations may be indicated depending on clinical context:

(Reproduced with permission from The Royal Australian College of General Practitioners from Troy L, Corte T. Interstitial Lung Disease in 2015: Where Are We Now? Aust Fam Physician 2015;44(8):546–52 .)

Treatment

The treatment of ILD is dependent on the classification or the presence of an underlying cause. To date, most research on treatment has focused on idiopathic pulmonary fibrosis (IPF), the most common idiopathic interstitial pneumonia.

IPF treatment: Two antifibrotic agents have been approved for use in IPF: pirfenidone, an oral antifibrotic drug, and nintedanib, an oral tyrosine kinase inhibitor. Studies suggest that these drugs slow the rate of decline in forced vital capacity but do not reverse established fibrosis. Side effects of pirfenidone include nausea, dyspepsia, fatigue, and photosensitivity. The primary side effect of nintedanib is diarrhea.

Nintedanib also decreases the rate of decline in patients with systemic sclerosis and progressive fibrosing interstitial lung disease.

Read more about a general approach to diagnosis and management of ILD.

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