Thoracic Pathology: A Volume in the High Yield Pathology Series 1st Edition

Desquamative Interstitial Pneumonia (DIP)

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

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Fig 1 Desquamative interstitial pneumonia. Large clusters of finely pigmented macrophages with abundant cytoplasm filling the alveoli in a uniform manner.

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Fig 2 Desquamative interstitial pneumonia. Minimal interstitial fibrosis without architectural distortion or honeycombing.

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Fig 3 Desquamative interstitial pneumonia. Pigmented alveolar macrophages within airspaces with a lymphocytic aggregate.



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