Desquamative interstitial pneumonia

Desquamative interstitial pneumonia (DIP) is an interstitial pneumonia closely related to, and thought to represent the end stage of respiratory bronchiolitis interstitial lung disease (RB-ILD)¹. It is associated with heavy smoking.

Demographics and clinical presentation

There is a recognised male predilection (2:1). The vast majority of patients are heavy smokers (90%) with an average smoking history of 18 pack-years. However, other predisposing factors include:

• systemic disorders, e.g. rheumatoid arthritis, scleroderma ⁷
• infection, e.g. HIV ⁴
• occupational or environmental exposure, e.g. asbestos ^6-7
• drugs

Presentation tends to be in middle age (30 - 60-60 years of age) with progressive shortness of breath and chronic cough ⁴.

Pathology

Its name is misleading as no desquamation of alveolar epithelium is present, but rather the cells that fill the alveoli are pigment laden macrophages. This is more pronounced than in RB-ILD.

Radiographic features

Plain film (CXR)

• non specificnonspecific
• may show bilateral interstitial infiltrates ⁸

HRCT

DIP is characterized by diffuse ground-glass opacities, which correlate histologically with the spatially homogeneous intraalveolar accumulation of macrophages and thickening of alveolar septa:

• bilateral and symmetric : 86(86%) ⁷
• basal and peripheral : 60(60%)
• patchy : 20(20%)
• diffuse : 20(20%) ⁴

Other frequent CT findings include spatially limited, irregular linear opacities and small cystic spaces, which are indicative of fibrotic change (50% of patients ⁷).

Other changes related to background smoking-related lung disease are often seen, e.g. bronchial wall thickening and centrilobular emphysema.

Despite differences in the CT appearance of RB-ILD and DIP, imaging findings may overlap and may be indistinguishable from each other. To improve diagnostic accuracy, lung biopsy is required in all cases of suspected RB-ILD or DIP.

Treatment and prognosis

With smoking cessation and corticosteroid therapy, the prognosis is good. Nevertheless, progressive disease with eventual death can occur, notably in patients with continued cigarette smoking.

Differential diagnosis

See > differential differential for ground glass opacities