Interstitial Pneumonias

Desquamative interstitial pneumonia

• Diffuse, temporally uniform, mild interstitial inflammation and fibrosis
• Many alveolar macrophages with light brown pigment (PAS-D+)
• Type II cell hyperplasia
• Little honeycombing

Most patients are smokers. Lesions are similar to those of respiratory bronchiolitis (see below) but more diffuse.

Respiratory bronchiolitis

Fibrous scar surrounds terminal and respiratory bronchioles. Large numbers of alveolar macrophages with light brown pigment (PAS-D+) fill adjacent alveoli. More peripheral alveoli are spared.

When this lesion causes cough and dyspnea accompanied by radiographic opacities, it is known as respiratory bronchiolitis-interstitial lung disease, a rare occurrence.

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