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9-20: Interstitial Lung Disease (Diffuse Parenchymal Lung Disease)

Meghan E. Fitzpatrick; Niall T. Prendergast; Belinda Rivera-Lebron

ESSENTIALS OF DIAGNOSIS

ESSENTIALS OF DIAGNOSIS

  • Insidious onset of progressive dyspnea and nonproductive chronic cough.

  • Tachypnea, bibasilar dry rales; digital clubbing and right heart failure with advanced disease.

  • Chest radiographs with patchy distribution of ground glass, reticular, nodular, reticulonodular, or cystic opacities.

  • Reduced lung volumes, pulmonary diffusing capacity, and 6-minute walk distance; hypoxemia with exercise.

Interstitial lung disease, or diffuse parenchymal lung disease, comprises a heterogeneous group of disorders that share common presentations (dyspnea), physical findings (late inspiratory crackles), and chest radiographs (septal thickening and reticulonodular changes).

The term “interstitial” is misleading since the pathologic process usually begins with injury to the alveolar epithelial or capillary endothelial cells (alveolitis). Persistent alveolitis may lead to obliteration of alveolar capillaries and reorganization of the lung parenchyma, accompanied by irreversible fibrosis. The process does not affect the airways proximal to the respiratory bronchioles. Table 9–16 outlines a selected list of differential diagnoses of interstitial lung disease. In most patients, no specific cause can be identified. In the remainder, the principal causes are medications, a variety of organic and inorganic dusts, and connective tissue diseases. The history—particularly the occupational and medication history—may provide evidence of a specific cause. The presence of diffuse parenchymal lung disease in the setting of an established connective tissue disease, such as rheumatoid arthritis, SLE, systemic sclerosis (scleroderma), polymyositis-dermatomyositis, Sjögren syndrome, and other overlap conditions, is suggestive of the cause. In some cases, lung disease precedes the more typical manifestations of the underlying connective tissue disease by months or years.

Table 9–16.Differential diagnosis of interstitial lung disease (listed alphabetically within category).
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Table 9–16. Differential diagnosis of interstitial lung disease (listed alphabetically within category).

Medication-related

 Antiarrhythmic agents (amiodarone)

 Antibacterial agents (nitrofurantoin, sulfonamides)

 Antineoplastic agents (bleomycin, cyclophosphamide, methotrexate, nitrosoureas)

 Antirheumatic agents (gold salts, penicillamine)

 Phenytoin

Environmental and occupational (inhalation exposures)

 Dust, inorganic (asbestos, beryllium, hard metals, silica)

 Dust, organic (thermophilic actinomycetes, avian antigens, Aspergillus species)

 Gases, fumes, and vapors (chlorine, isocyanates, paraquat, sulfur dioxide)

 Ionizing radiation

 Talc (injection drug users)

Infections

 Fungus, disseminated (Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum)

 Mycobacteria, disseminated

 Pneumocystis jirovecii

 Viruses

Primary pulmonary disorders

 Cryptogenic organizing pneumonia

 Idiopathic interstitial pneumonia: acute interstitial pneumonia, desquamative interstitial pneumonia, nonspecific interstitial pneumonia, usual interstitial pneumonia, respiratory bronchiolitis–associated interstitial lung disease

 Pulmonary alveolar proteinosis

Systemic disorders

 Acute respiratory distress syndrome

 Amyloidosis

 Ankylosing spondylitis

 Autoimmune disease: dermatomyositis, polymyositis, rheumatoid arthritis, SLE, systemic sclerosis (scleroderma)

 Chronic eosinophilic pneumonia

 Goodpasture syndrome

 Granulomatosis polyangiitis

 IBD

 Idiopathic pulmonary hemosiderosis

 Langerhans cell histiocytosis (eosinophilic granuloma)

 Lymphangitic spread of cancer (lymphangitic carcinomatosis)

 Lymphangioleiomyomatosis

 Pulmonary edema

 Pulmonary venous hypertension, chronic

 Sarcoidosis

Known causes of interstitial lung disease are dealt with in their specific sections. The important idiopathic forms are discussed below.

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