Respiratory bronchiolitis-associated interstitial lung disease in a nonsmoker: radiologic and pathologic findings

Cigarette smoking decreases macrophage-dependent clearance to impact the biological effects of occupational and environmental particle exposures

The retention of occupational and environmental particles in the lung is a primary determinant of biological effects. In the distal respiratory tract, particle clearance includes phagocytosis by alveolar macrophages (AMs), migration to the terminal bronchiole, and transport of AMs and particles by the mucociliary escalator. With increasing particle exposure, a focal collection of particle-laden macrophages results at the respiratory bronchiole (RB) which is that site in the clearance pathway demanding the greatest traverse by these cells after a commencement from the alveoli. With the greatest particle doses, there is "particle overload" and impaired mobility which is reflected by an excess accumulation of particle-laden macrophages throughout the RBs, alveolar ducts, and alveoli. With deposition of fibrous particles in the distal respiratory tract, the AM is unable to extend itself to enclose fibers with a major diameter of 10-20 microns or longer resulting in "frustrated phagocytosis" and longer retention times. Clearance pathways for particles are shared. There can be a summation of particle exposures with exhaustion in the capacity of the AMs for transport. Cigarette smoking (CS) is the greatest particle challenge humans encounter. Associated with its enormous magnitude, CS profoundly impacts the clearance pathways and subsequently interacts with other particle exposures to increase biological effects. Interstitial lung disease, pulmonary function, chronic obstructive pulmonary disease, infections, lung cancer, and mortality can be altered among smokers exposed to occupational and environmental particles (e.g., silica, coal mine dust, air pollution particles, other particles, and asbestos). It is concluded that both decreasing CS and controlling particle exposures are of vital importance in occupational and environmental lung disease.

Multidisciplinary Approach to the Diagnosis of Idiopathic Interstitial Pneumonias: Focus on the Pathologist's Key Role

Idiopathic Interstitial Pneumonias (IIPs) are a heterogeneous group of the broader category of Interstitial Lung Diseases (ILDs), pathologically characterized by the distortion of lung parenchyma by interstitial inflammation and/or fibrosis. The American Thoracic Society (ATS)/European Respiratory Society (ERS) international multidisciplinary consensus classification of the IIPs was published in 2002 and then updated in 2013, with the authors emphasizing the need for a multidisciplinary approach to the diagnosis of IIPs. The histological evaluation of IIPs is challenging, and different types of IIPs are classically associated with specific histopathological patterns. However, morphological overlaps can be observed, and the same histopathological features can be seen in totally different clinical settings. Therefore, the pathologist's aim is to recognize the pathologic-morphologic pattern of disease in this clinical setting, and only after multi-disciplinary evaluation, if there is concordance between clinical and radiological findings, a definitive diagnosis of specific IIP can be established, allowing the optimal clinical-therapeutic management of the patient.

Air trapping in small airway diseases: A review of imaging technique and findings with an overview of small airway diseases

Air trapping is a common finding radiologists encounter on CT imaging of the thorax. This term is used when there are geographic areas of differing attenuation within the lung parenchyma. Most commonly, this is the result of abnormal retention of air due to complete or partial airway obstruction from small airway pathologies. Perfusional differences due to underlying vascular diseases could also result in these appearances, and hence, inspiratory and full expiratory phase CT studies are required to accurately diagnose air trapping. It is important to note that this can occasionally be present in healthy patients. Multiple diseases are associated with air trapping. Determining the aetiology relies on accurate patient history and concomitant findings on CT. There is currently no consensus on accurate assessment of the severity of air trapping. The ratio of mean lung density between expiration and inspiration on CT and the change in lung volume have demonstrated a positive correlation with the presence of small airway disease. Treatment and resultant patient outcome depend on the underlying aetiology, and hence, radiologists need to be familiar with the common causes of air trapping. This paper outlines the most common disease processes leading to air trapping, including Constrictive bronchiolitis, Hypersensitivity pneumonitis, DIPNECH, and Post-infectious (Swyer-James/Macleod). Various diseases result in the air trapping pattern seen on the expiratory phase CT scan of the thorax. Combining patient history with other concomitant imaging findings is essential for accurate diagnosis and to further guide management.

The Occupational Burden of Nonmalignant Respiratory Diseases. An Official American Thoracic Society and European Respiratory Society Statement

Rationale: Workplace inhalational hazards remain common worldwide, even though they are ameliorable. Previous American Thoracic Society documents have assessed the contribution of workplace exposures to asthma and chronic obstructive pulmonary disease on a population level, but not to other chronic respiratory diseases. The goal of this document is to report an in-depth literature review and data synthesis of the occupational contribution to the burden of the major nonmalignant respiratory diseases, including airway diseases; interstitial fibrosis; hypersensitivity pneumonitis; other noninfectious granulomatous lung diseases, including sarcoidosis; and selected respiratory infections. Methods: Relevant literature was identified for each respiratory condition. The occupational population attributable fraction (PAF) was estimated for those conditions for which there were sufficient population-based studies to allow pooled estimates. For the other conditions, the occupational burden of disease was estimated on the basis of attribution in case series, incidence rate ratios, or attributable fraction within an exposed group. Results: Workplace exposures contribute substantially to the burden of multiple chronic respiratory diseases, including asthma (PAF, 16%); chronic obstructive pulmonary disease (PAF, 14%); chronic bronchitis (PAF, 13%); idiopathic pulmonary fibrosis (PAF, 26%); hypersensitivity pneumonitis (occupational burden, 19%); other granulomatous diseases, including sarcoidosis (occupational burden, 30%); pulmonary alveolar proteinosis (occupational burden, 29%); tuberculosis (occupational burden, 2.3% in silica-exposed workers and 1% in healthcare workers); and community-acquired pneumonia in working-age adults (PAF, 10%). Conclusions: Workplace exposures contribute to the burden of disease across a range of nonmalignant lung conditions in adults (in addition to the 100% burden for the classic occupational pneumoconioses). This burden has important clinical, research, and policy implications. There is a pressing need to improve clinical recognition and public health awareness of the contribution of occupational factors across a range of nonmalignant respiratory diseases.

Pulmonary effects of i.v. injection of crushed oral tablets: "excipient lung disease"

OBJECTIVE

When crushed oral tablets are injected i.v., their filler material (excipient) can induce a potentially fatal foreign-body reaction in pulmonary arterioles, presenting as dyspnea and pulmonary hypertension with centrilobular nodules on CT. We will describe the imaging and pathologic features of "excipient lung disease."

CONCLUSION

The radiologist has a critical role in recognizing and reporting excipient lung disease because the referring clinician may be unaware of the patient's i.v. drug abuse.

Respiratory bronchiolitis-interstitial lung disease

Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) is a rare, mild inflammatory pulmonary disorder that occurs almost exclusively in current or former heavy smokers, usually between the third and sixth decades, most likely with no gender predilection. The onset is usually insidious with exertional dyspnea and persistent cough, which may be non-productive, developing over a course of weeks or months. RB-ILD may also be diagnosed in asymptomatic patients with functional impairment and chest radiograph or high-resolution computed tomography (HRCT) abnormalities. Histologically, RB-ILD is characterized by the accumulation of yellow-brown pigmented macrophages within the lumens of respiratory bronchioles and alveolar ducts, associated with a patchy submucosal and peribronchiolar chronic inflammation. Common findings also include mild bronchiolar and peribronchiolar alveolar fibrosis that expands contiguous alveolar septa and leads to architectural distortion as well as centrilobular emphysema. Chest radiographs in patients with RB-ILD typically show fine reticulonodular interstitial opacities, while on HRCT central and peripheral bronchial wall thickening, centrilobular nodules, and ground-glass opacities associated with upper lobe centrilobular emphysema are most frequently reported. Pulmonary function testing may be normal but usually demonstrates mixed, predominantly obstructive abnormalities, often combined with hyperinflation and usually associated with a mild to moderate reduction in carbon monoxide diffusion capacity (DLco). The course of RB-ILD is heterogeneous. Some patients respond favorably to corticosteroids and/or smoking cessation, but often there is no functional improvement and the disease progresses despite smoking cessation and treatment.

Pathology of small airways disease

CONTEXT

The term small airways disease encompasses a generally poorly understood group of lung diseases that may arise primarily within the small airways or secondarily from diseases primarily affecting the bronchi or lung parenchyma. Their histology may be confusing; however, because treatments and prognoses vary, correct pathologic diagnosis is important.

OBJECTIVE

To present a nonexhaustive review of the pathology of primary and secondary small airways diseases, including small airways disease related to tobacco; to various other exposures, including mineral dusts; to diseases involving other areas of the lung with secondary bronchiolar involvement; and to recently described bronchiolitic disorders.

DATA SOURCES

Current literature is reviewed.

CONCLUSIONS

Small airways diseases include a wide variety of diseases of which the pathologist must consider. Uncommon conditions such as diffuse idiopathic neuroendocrine cell hyperplasia and diffuse panbronchiolitis may show relatively specific diagnostic features histologically; however, most small airways diseases exhibit nonspecific histologic features. Conditions not considered primary pulmonary diseases, such as collagen vascular diseases, bone marrow transplantation, and inflammatory bowel disease, must also be considered in patients with small airways changes histologically. Clinical and radiologic correlation is important for obtaining the best possible diagnosis.

Small Airways Disease

Small airways diseases are best defined pathologically as a diverse group of conditions that primarily involve bronchioles and acartilagenous airways 2 mm or less in diameter, which include membranous bronchioles, respiratory bronchioles, and alveolar ducts. Small airways can be involved with disease primarily or secondarily. The concept of small airways disease varies among specialties, with clinicians generally considering them in terms of terminal airway changes causing airflow obstruction, radiologists considering them in the context of direct signs and indirect signs identified on high-resolution computed tomography scans, and pathologists evaluating them based entirely or almost entirely on the histologic changes present in the bronchioles, with or without associated changes involving bronchi and alveoli. The histologic features of small airways diseases may be confusing because they overlap. There may be incomplete assessment of the histologic process with limited biopsy. Other disease processes may occur along with a small airways disease, and may obscure or confound its histologic features. This article focuses on the histologic changes diagnostic of a variety of primary and secondary small airways diseases. Because the histologic features involve bronchioles, gross findings are often minimal and/or nonspecific. The article provides a nonexhaustive examination of conditions and diseases involving the small airways, focusing on the microscopic features, with emphasis on the limitations of histologic diagnosis and differential diagnosis.