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.

Epidemiology

It is considered one of the rarest of idiopathic interstitial pneumonias . 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 .

The vast majority of patients are heavy smokers (90%) with an average smoking history of 18 pack-years. However, other predisposing factors include:

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 .

Radiographic features

Plain radiograph
  • nonspecific
  • may show bilateral interstitial infiltrates : they may have a greater predilection for the lower-lung zones and, sometimes, peripheral predominance
  • 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
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%) 
  • basal and peripheral (60%)
  • patchy (20%)
  • diffuse (20%) 

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

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  .

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 . 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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