Respiratory bronchiolitis–associated interstitial lung disease is a form of idiopathic interstitial pneumonia Overview of Idiopathic Interstitial Pneumonias Idiopathic interstitial pneumonias (IIPs) are interstitial lung diseases of unknown etiology that share similar clinical and radiologic features and are distinguished primarily by the histopathologic... read more .
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 Hypersensitivity Pneumonitis Hypersensitivity pneumonitis is a syndrome of cough, dyspnea, and fatigue caused by sensitization and subsequent hypersensitivity to environmental (frequently occupational or domestic) antigens... read more 
(usually due to mineral dusts), viral infections, and drug reactions.
RBILD also resembles desquamative interstitial pneumonia Desquamative Interstitial Pneumonia Desquamative interstitial pneumonia is chronic lung inflammation characterized by mononuclear cell infiltration of the airspaces; it occurs almost exclusively in current or former cigarette... read more 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 Idiopathic Pulmonary Fibrosis Idiopathic pulmonary fibrosis (IPF), the most common form of idiopathic interstitial pneumonia, causes progressive pulmonary fibrosis. Symptoms and signs develop over months to years and include... read more 
, but are milder. Crackles on examination are the only physical finding.
Diagnosis
Chest x-ray
High-resolution CT (HRCT)
Sometimes surgical lung biopsy
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:
Bronchial wall thickening
Diffuse, fine reticular or nodular opacities
Prominent peribronchovascular interstitium
Small peripheral ring shadows
Small regular and irregular opacities
HRCT often shows centrilobular nodules and patchy areas of hazy ground-glass opacities.
A mixed obstructive-restrictive pattern is a common pulmonary function test Overview of Tests of Pulmonary Function Pulmonary function tests provide measures of airflow, lung volumes, gas exchange, response to bronchodilators, and respiratory muscle function. Basic pulmonary function tests available in the... read more 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
Smoking cessation
Treatment of respiratory bronchiolitis–associated interstitial lung disease is smoking cessation Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more 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.
