Respiratory bronchiolitis – associated interstitial lung disease (RB-ILD)

Clinical History

Areas of ground-glass opacification and centrilobular nodules in a patient with respiratory bronchiolitis – associated interstitial lung disease.

Imaging Findings

A 32 year-old male patient, heavy smoker (average exposure of 35 pack-years), presented to our institution refering dyspnea and dry cough, for three months. He denied any professional, ambiental or drug exposure. Crackles and rhonchi on chest auscultation were noted on physical examination. Pulmonary function tests revealed obstructive abnormalities. The chest radiogram was unremarkable. High-resolution CT of the chest was performed and showed ill-defined nodules, with a centrilobular distribution and upper lobe predominance (figure 1), associated with widespread areas of ground-glass opacification (figure 2) and a bulla in the anterior segment of the right upper lobe (figure 3). Scans at the end of expiration showed areas of air trapping (figure 4). The diagnosis of respiratory bronchiolitis – associated interstitial lung disease was made after performing a lung biopsy, which revealed pigmented macrophages within respiratory bronchioles. Both clinical symptoms and lung function analysis improved significantly following smoking cessation.

Discussion

Respiratory bronchiolitis, RB-ILD and desquamative interstitial pneumonia (DIP) are considered to be part of a spectrum of smoking-related lung injuries. As a clinical diagnosis RB-ILD is very rare and is associated with patients who are heavy smokers (average exposure of more than 30 pack-years). This condition is thought to represent an exaggerated respiratory bronchiolitis response, resulting in substantial pulmonary symptoms, abnormal pulmonary function and imaging abnormalities (1, 2, 3). It is characterized histologically by bronchiolocentric accumulation of pigmented alveolar macrophages and fibrotic or cellular inflammatory changes of pulmonary interstitium (4). Fibrosis is minimal. DIP is also characterized by the presence of intra-alveolar macrophages, but the abnormalities are more diffuse (1). In most cases RB-ILD manifestations are subclinical and detected coincidentally. Lung function analysis reveals only minor restrictive or obstructive defects in most cases, often combined with hyperinflation (4).Chest radiograph is non-specific and may show bilateral lower zone reticular shadowing. HRCT features include extensive bilateral ground-glass opacities and centrilobular nodularity, mostly in a patchy distribution. There may also be present bronchial wall thickening, very mild fibrosis with interlobular septal thickening, upper zone centrilobular emphysema and areas of reduced lung density due to air trapping (2, 3, 4). The CT findings of RB-ILD may be similar to those of hypersensitivity pneumonia (clinical differentiation facilitated by exposure history), non-specific interstitial pneumonia (NSIP), DIP, lymphoid interstitial pneumonia (LIP) and infections such as Pneumocystis carinii pneumonia. Apart from the presence of some distinguishing clinical and imagiological features (such as cysts, which may be present in DIP and LIP), histological evaluation is often important (1, 3, 4). Complete recovery is usually possible with smoking-cessation and corticosteroid therapy is usually not necessary (4).

Differential Diagnosis List

Final Diagnosis

Respiratory bronchiolitis – associated interstitial lung disease

URL:	https://www.eurorad.org/case/5350
DOI:	10.1594/EURORAD/CASE.5350
ISSN:	1563-4086