Pulmonary Pathology Online
Pathology of Desquamative Interstitial Pneumonia (DIP)
interstitial pneumonia (DIP), also known as alveolar macrophage
pneumonia (AMP), represents a subset of idiopathic interstitial
pneumonia that responds better to steroids and has a more favourable
prognosis than usual interstitial pneumonia.
Desquamative interstitial pneumonia (DIP) is an uncommon disease characterized by interstitial inflammation and a striking accumulation of macrophages in the alveoli.
It is important to recognize that desquamative interstitial pneumonia has distinctive clinical features, prognosis, and response to treatment.
The patients are younger than those with usual interstitial pneumonia (mean age of 46 years), the symptoms are of shorter duration (2 to 3 years), and the chest radiographs show a fine density (ground glass opacity), most obvious in the costophrenic angles.
Pulmonary function changes are slight, and lung volumes do not change.
The pathogenesis and etiology of DIP are not clear.
Views regarding Desquamative interstitial pneumonia (DIP):
- On the one hand, DIP was considered to be part of the spectrum of the histological appearances seen in cryptogenic fibrosing alveolitis being an early cellular rather than interstitial phase of the disease.
- The alternative view recognizes the DIP as a pattern of lung injury the clinical manifestations, radiological appearances and prognosis of which are all significantly different from those of UIP.
They also tended to be younger and heavy smokers, and very few of them had honeycomb changes on x-rays.
Desquamative interstitial pneumonia patients respond well to steroids, survive much longer and some of them recover without treatment, in sharp contrast to UIP patients who show little response to steroids,have very poor prognosis and so far no spontaneous recovery has been recorded.
Microscopic features: Histologicaly, DIP is characterized by a temporally homogeneous disease process, with uniform changes at low power examination.
Desquamative interstitial pneumonia is diagnosed by the presence of airspaces stuffed with macrophages. Large numbers of macrophages are present in the alveolar lumina.
These are usually evenly distributed, and often contain fine pale brown pigment.
It was originally thought that the cells in the airspaces are desquamated type II epithelial cells, an interpretation that gave the condition its name.
However, electron microscopy has shown that the cells are macrophages.
The lung architecture remains intact, so that the alveoli are readily recognized.
There is minimal inflammation. The walls display a mild mononuclear infiltrate, and there is type II metaplasia of the alveolar lining cells.
There is generally only mild to moderate interstitial fibrosis.
Some multinucleate histiocytic cells are often present.
Unlike UIP,honeycomb changes or fibroblast foci are only occasionally seen in cases of DIP (but if both these features are present together in a biopsy showing otherwise features of DIP, then the diagnosis of UIP should be seriously considered).
The accumulation of macrophages tends to be seen throughout the secondary lobules although there may be some centri-lobular accentuation of the process, often with associated respiratory bronchiolitis (so there is overlap with RB-ILD).
It is important to confirm the histiocytic nature of the intra-alveolar cells with the appropriate macrophage marker as aggregates of carcinoma cells can occasionally mimic macrophages.
It should be pointed out that DIP is a pattern of response to lung injury and that non-specific DIP-like reactions are seen in many pathological conditions such as UIP, Langerhans cell histiocytosis (LCH), asbestosis and other forms of chronic interstitial pneumonias, and adjacent to tumors.
Idiopathic Pulmonary Fibrosis ; Usual Interstitial Pneumonia (UIP) ; Non-specific interstitial pneumonia (NSIP) ; Respiratory bronchiolitis-interstitial lung disease (RBILD) ; Acute interstitial pneumonia (AIP)/organizing diffuse alveolar damage DAD); Lymphocytic Interstitial Pneumonia / Follicular Bronchiolitis .
Respiratory bronchiolitis, respiratory bronchiolitis-associated interstitial lung disease, and desquamative interstitial pneumonia: different entities or part of the spectrum of the same disease process?
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