The term RB-ILD covers a form of IIP which is also termed “condensation or smoker’s pneumonia” in German. Here, the cause is generally excessive smoking, with the development of bronchiolitis (respiratory bronchiolitis, RB). In pure RB, patients only have collapse of the small airways. In some patients the disease can take on more severe forms, however, in which case there are numerous pigmented macrophages intraluminally and mild to moderate clinical symptoms (dyspnoea, hypoxaemia). We then talk of RB-ILD. DIP was originally interpreted by Liebow as an expression of desquamation of the alveolar epithelium and thus it is also termed desquamative interstitial pneumonia. We now know that the accumulation of cells in the distal airways and alveoli in this form is of macrophages, as in RB-ILD. Histologically, the picture of DIP is similar to RB-ILD, but the distribution pattern is much more homogeneous and does not even have the bronchiolocentric distribution. There is also mild peribronchial fibrosis and extensive hyperplasia of the alveolar type II cells. The bronchiolocentric lesions are usually combined with centrilobular emphysema. DIP thus very likely represents one spectrum and RB-ILD another spectrum of a common disease which only differs in the degree to which the different compartments are accentuated (like bronchiolitis obliterans and organising pneumonia).
There are no exact figures on the incidence. RB-ILD and DIP patients show long-term and persistent nicotine abuse and are between 40-50 years old.
The aetiology has not been elucidated although it is very likely a process directly triggered by smoking.
The clinical symptoms consist of slowly developing dyspnoea and dry cough, and approximately half the patients have finger clubbing. On lung function tests, restrictive ventilatory impairment and abnormal diffusion are prominent findings.
On HRCT, there is a ground glass appearance, being most prominent in the lower fields and periphery and are sometimes patchy and sometimes homogeneous. There are also centrilobular nodes and condensations of the central and peripheral airways. Centrilobular emphysema which is most marked in the upper lung fields is often also an accompanying feature. Simultaneously there are often patchily distributed hypodensities, which represent local air trapping. Although reticular markings are common, they are usually only mild.
On BAL, the lavage fluid itself often shows yellow-brownish discoloration, the alveolar macrophages seen in increased numbers have yellow, gold, brown or black pigments; eosinophils, neutrophils and lymphocytes may be present to a slightly increased extent.
The clinical symptoms and lung function disorder generally undergo marked regression although there are still no systematic studies on this issue in large populations. Steroids may also be administered as an adjunctive measure.