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). It is associated with heavy smoking.
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Epidemiology
It is considered one of the rarest of idiopathic interstitial pneumonias 11. There is a recognized male predilection (M:F = 2:1).
Clinical presentation
Presentation tends to be in middle age (30-60 years of age) with progressive shortness of breath and chronic cough 4.
The vast majority of patients are heavy smokers (90%) with an average smoking history of 18 pack-years. However, other predisposing factors include:
- autoimmune/systemic disorders, e.g. rheumatoid arthritis, scleroderma 7
- infection, e.g. HIV 4
- toxin, occupational or environmental exposure, e.g. asbestos 6,7
- drugs
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.
Pulmonary function tests
Pulmonary restriction is usually absent or slight, although diffusion is impaired in most patients 9.
Radiographic features
Plain radiograph
- nonspecific
- may show bilateral interstitial infiltrates 8: they may have a greater predilection for the lower-lung zones and, sometimes, peripheral predominance 9
- has been classically described as one of triangular-shaped regions of increased density radiating from the hilar regions to the periphery; although, this is seen in only a minority of cases 10
CT
DIP is usually characterized by diffuse ground-glass opacities (sometimes has a granular or nodular texture), which correlate histologically with the spatially homogeneous intra-alveolar accumulation of macrophages and thickening of alveolar septa:
- bilateral and symmetric (86%) 7
- basal and peripheral (60%)
- patchy (20%)
- diffuse (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.
Honeycombing may be seen in less than one-third of cases, and if present tends to be usually peripheral and limited in extent 9.
Treatment and prognosis
With smoking cessation and corticosteroid therapy, the prognosis is good. The overall prognosis of has been described as being significantly better than that of fibrotic NSIP 11. Nevertheless, progressive disease with eventual death can occur, notably in patients with continued cigarette smoking.
Differential diagnosis
For diffuse ground glass changes on CT consider the differential for ground glass opacities.
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