Definition
• Fairly uncommon interstitial lung disease with characteristic clusters of pigmented macrophages within the distal airspaces that were initially thought to be desquamated pneumocytes, hence the name desquamative interstitial pneumonia
• Considered by many to be on the same spectrum of disease as respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)
• Has overlapping histological and epidemiological features with RB-ILD
• DIP and RB-ILD likely represent different spectra of a single, smoking-related interstitial lung disease
Clinical features
Epidemiology
• Affects middle-aged adults; mean age, 50 years
• Male to female ratio, 2:1
• Age of onset is 10 year earlier than usual interstitial pneumonia (UIP)
• Majority of patients are or were smokers
• Might be associated with sirolimus treatment
Presentation
• Insidious onset of dyspnea, coughing, and/or chest pain over a period of weeks to months
Prognosis and treatment
• Nonprogressive disease with 100% 10-year survival rate
• Corticosteroids are the mainstay of treatment
• Macrophages can persist long after cessation of cigarette smoking
Pathology
Histology
• Cohesive clusters of pigmented alveolar macrophages with granular brown pigment within abundant cytoplasm filling the distal airspaces in a uniform manner
• Mild uniform interstitial fibrosis without architectural distortion or honeycombing
• Few multinucleated giant cells, lymphocytes; rarely, eosinophils may be admixed with macrophages
• Cuboidal hyperplasia of type II pneumocytes with mild bronchiolar fibrosis and inflammation
• Mild chronic inflammation with scattered lymphoid aggregates, often with germinal centers
• Round or oval, intraalveolar, laminated “blue bodies” may be present
• Medial and intimal thickening of vascular structures
• Other findings include pleural inflammation and fibrosis and dilated pleural lymphatics
• Negative findings: architectural remodeling, honeycombing, dense fibrosis or fibroblastic foci
Immunopathology/special stains
• Prussian blue weakly stains the granular pigment within macrophages; can be distinguished from coarse brown hemosiderin granules associated with pulmonary hemorrhage
Main differential diagnoses
• RB-ILD: on the opposite spectrum of the same disease process with more inflammation, extensive and diffuse changes, bronchiolocentric accumulation of macrophages with sparing of distal airspaces
• UIP: has architectural distortion, honeycombing, and fibroblastic foci
• Nonspecific interstitial pneumonia: interstitial inflammation and mild fibrosis
• Eosinophilic pneumonia
• Alveolar hemorrhage syndromes: contain iron granules caused by chronic hemorrhage
• Histiocyte-rich infections: Mycobacterium avium-intracellular, Cryptococcus, and Rhodococcus equi
• HIV-associated lung disease
• Carcinoma with intraalveolar growth pattern: has nuclear atypia with keratin-positive tumor cells
• Focal, nonspecific DIP-like reaction: present around scar, tumor, or infarction and may represent RB-ILD
Fig 1 Desquamative interstitial pneumonia. Large clusters of finely pigmented macrophages with abundant cytoplasm filling the alveoli in a uniform manner.
Fig 2 Desquamative interstitial pneumonia. Minimal interstitial fibrosis without architectural distortion or honeycombing.
Fig 3 Desquamative interstitial pneumonia. Pigmented alveolar macrophages within airspaces with a lymphocytic aggregate.