respiratory bronchiolitis

Respiratory bronchiolitis (RB) and desquamative interstitial pneumonia (DIP) are widely regarded as being related to each other and representing the opposite ends of the spectrum of a type of smoking-induced respiratory disease.

RB is characterized by accumulation of tobacco pigment-laden macrophages within and obstructing terminal airways and, to a limited extent, in peribronchiolar alveoli. Terminal airways may also exhibit some inflammation and scarring.

RB is usually asymptomatic and is most often encountered as an incidental finding in lung cancer resection specimens.

In a small number of patients presenting with significant dyspnea, hypoxemia and radiographic abnormalities RB may be the only finding in a lung biopsy specimen.

This small group of patients is considered to have RB-ILD (respiratory bronchiolitis-interstitial lung disease).

Some of these patients do have airway-centered interstitial fibrosis but in general interstitial disease is not well documented in patients with RB-ILD.

It is possible that foci of atelectasis distal to obstructed bronchioles may account for some of the radiographic abnormalities.

Diffuse filling of alveoli with tobacco-pigmented macrophages throughout the lungs is the characteristic feature of DIP and lesions of RB may be seen in these cases as well.

DIP as classically described is a rare lesion. Individuals with RB and DIP are smokers with rare exception. RB can be considered to DIP as bronchopneumonia is to lobar pneumonia.

Links

 Respiratory bronchiolitis (RB) and desquamative interstitial pneumonia (DIP) at the Yale Rosen Collection

Microscopy

 peribronchiolar pigmented macrophages
 chronic inflammation
 goblet cell metaplasia