Respiratory Bronchiolitis–Associated Interstitial Lung Disease
Respiratory bronchiolitis–associated interstitial lung disease is a form of idiopathic interstitial pneumonia.
Most smokers develop a subclinical bronchiolitis characterized by mild or moderate inflammation of the small airways. The few patients who develop more severe inflammation with clinically significant interstitial disease are said to have RBILD. Male-to-female ratio is 2:1.
RBILD is characterized histologically by submucosal inflammation of the membranous and respiratory bronchioles manifested by the presence of tan-brown pigmented macrophages (resulting from increased iron content, as occurs in smokers), mucus stasis, and metaplastic cuboidal epithelium in bronchioles and alveoli. Alveolar septal scarring always occurs. Similar findings, however, occur in some hypersensitivity reactions, occupational lung exposures (usually due to mineral dusts), viral infections, and drug reactions.
RBILD also resembles desquamative interstitial pneumonia histologically, but in RBILD, inflammation is patchier and less extensive. The similarity of the 2 conditions has led to the suggestion that they are different manifestations of the same disease caused by cigarette smoking.
Symptoms of cough and breathlessness during exertion resemble those of other interstitial lung diseases, especially idiopathic pulmonary fibrosis, but are milder. Crackles on examination are the only physical finding.
Diagnosis of respiratory bronchiolitis–associated interstitial lung disease is considered in patients being evaluated for interstitial lung disease. Diagnostic testing includes imaging tests and biopsy.
Chest x-ray findings include the following:
HRCT often shows centrilobular nodules and patchy areas of hazy ground-glass opacities.
A mixed obstructive-restrictive pattern is a common pulmonary function test finding, although results may be normal or show an isolated increase in residual volume. Routine laboratory tests are not helpful.
Surgical lung biopsy is sometimes obtained if the diagnosis remains unclear and a trial of smoking cessation has not decreased symptoms.
Treatment of respiratory bronchiolitis–associated interstitial lung disease is smoking cessation and avoidance of even passive cigarette smoke exposure, which may prevent improvement or lead to recurrence of the illness. There is only anecdotal evidence of the efficacy of corticosteroids.
The natural clinical course of the disease is unknown, but prognosis is good with smoking cessation.