Interstitial (Nonidiopathic) Pulmonary Fibrosis

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Background

Diffuse parenchymal lung diseases (DPLDs) comprise a heterogenous group of disorders. Clinical, physiologic, radiographic, and pathologic presentations of patients with these disorders are varied (an example is shown in the image below). However, a number of common features justify their inclusion in a single disease category.


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Frontal chest radiograph demonstrating bilateral reticular and nodular interstitial infiltrates with upper zone predominance.

DPLD may be idiopathic, a classic illustration of which is idiopathic interstitial fibrosis (IPF), which is discussed in another article (see Pulmonary Fibrosis, Idiopathic). The underlying histopathology of IPF is usual interstitial pneumonitis (UIP). Other major histopathologic forms of idiopathic interstitial pneumonias include the following: desquamative interstitial pneumonia (DIP), respiratory bronchiolitis interstitial lung disease (RBILD), acute interstitial pneumonitis (AIP), also known as Hamman-Rich syndrome, nonspecific interstitial pneumonia (NSIP), cryptogenic organizing pneumonia (COP) (see Bronchiolitis Obliterans Organizing Pneumonia), and lymphocytic interstitial pneumonia (LIP) (see Lymphocytic Interstitial Pneumonia).

Some forms of DPLD are related to occupational, environmental, drug, and/or radiation exposure, as well as systemic illness such as collagen-vascular disease (see Collagen-Vascular Disease Associated With Interstitial Lung Disease). Another category of DPLDs includes granulomatous forms, such as sarcoidosis (see Sarcoidosis), and hypersensitivity pneumonia (HSP) (see Hypersensitivity Pneumonitis). Finally, a number of very rare forms of DPLDs exist, including pulmonary Langerhans cell histiocytosis (PLCH) (see Eosinophilic Granuloma (Histiocytosis X)), tuberous sclerosis, lymphangioleiomyomatosis (LAM) (see Lymphangioleiomyomatosis), and Hermansky-Pudlak syndrome.

Some of these disorders, for example, RBILD, DIP, and PLCH, are clearly associated with smoking. Some forms of DPLD, as noted above, may also be related to occupational, environmental, drug, radiation exposure, or systemic illness such as collagen-vascular disease. This article presents a broad overview, with an emphasis on those etiologies that result in pulmonary fibrosis not discussed elsewhere in this series.

Pathophysiology

A common pathophysiology has been postulated for these disorders. It is thought to begin with acute injury to the pulmonary parenchyma, leading to chronic interstitial inflammation, then to fibroblast activation and proliferation, and finally progressing to the common endpoint of pulmonary fibrosis and tissue destruction. Current research indicates that inflammation is less important in IPF, which appears to be primarily a disorder of fibroblast activation and proliferation in response to some as yet unknown trigger(s).

The DPLDs typically manifest with the insidious onset of respiratory symptomatology, although onset can be acute and rapidly progressive, as in COP or AIP.

Pathologically, all DPLDs manifest histologically with disease largely within the interstitial compartment of the lung. However, alveolar and airway architecture also may be disrupted to varying degrees. The histologic patterns of UIP, DIP, nonspecific interstitial pneumonitis (NSIP), HSP, LIP, COP, giant cell pneumonitis, and granulomatous pneumonitis are most common and are focused in the alveolar, lobular, and lobar septa, impacting alveoli, small airways, and pulmonary vasculature.

Epidemiology

Frequency

United States

As a group, diffuse interstitial diseases of the lung are uncommon. Based on the Bernalillo County, NM, USA registry data published in 1994, the overall estimated incidence is approximately 30 cases per 100,000 persons per year[1] . Rates of interstitial lung disease are somewhat higher in men than in women, and the epidemiology is markedly affected by age and occupational exposures. Of patients referred to a pulmonary disease specialist, an estimated 10-15% have a DPLD.

International

Although little published data exist comparing worldwide prevalence, significant differences are apparent. The Bernalillo County study estimated a prevalence of 80.9 cases per 100,000 population in men and 67.2 cases per 100,000 population in women. In comparison, a Japanese study estimated a prevalence of 4.1 cases per 100,000 population; a study in the Czech Republic reported 7-12 cases per 100,000 population; and data from a Finnish registry indicated 16-18 cases per 100,000 population.

Mortality/Morbidity

The natural history of diffuse interstitial lung diseases varies among different diagnostic entities and among individuals with the same diagnosis.

Race

Sex

Age

History

The clinical history offered by patients with a DPLD is variable and related to the underlying disease process. Many patients with DPLD, particularly IPF/UIP, may experience acute exacerbations of the disease with subsequent persistent decrement in lung function, which has become increasingly recognized.

Physical

Causes

Numerous causes/diagnoses are included among the DPLDs, many of which can be grouped as follows:

Laboratory Studies

Imaging Studies

Other Tests

Procedures

Histologic Findings

The histopathology observed in diffuse interstitial diseases of the lung is varied. The histopathologic classification of idiopathic interstitial pneumonias were updated by Katzenstein and Myers[7] in 1998 to include the following 4 subgroups: UIP, AIP (diffuse alveolar damage), DIP/RBILD, and NSIP. Different histopathologic patterns may also be found in biopsy samples from different regions of the lung in these patients, particularly those with NSIP. Sometimes interstitial lung diseases with known etiologies may manifest one of the preceding histopathologic patterns. In addition, other pathologic patterns may be found. These may be consistent with COP, granulomatous lung disease, HSP, giant cell pneumonitis (hard-metal pneumoconiosis), eosinophilic pneumonia, and LIP (lymphoproliferative disorder).

Interpretation of histopathologic findings may be difficult, even in experienced hands, and disagreement may occur even among expert pathologists.[8] In 2005, a 52% rate of disagreement between local general pathologists and "expert" pathologists was documented in a retrospective analysis.[9]

Staging

Pulmonary function studies and the 6-minute walk study have demonstrated prognostic utility in IPF with histopathologic findings of UIP and NSIP. A diminished diffusion capacity (DLCO) on initial evaluation is a poor prognostic indicator, regardless of histologic type. Egan et al[10] have proposed a classification scheme of advanced versus limited disease based on a cutoff value of DLCO greater or less than 40%. Similarly, a trough saturation of less than 88% during a 6-minute walk study has been shown to confer a worse prognosis. Serial decrements in functional vital capacity and DLCO over time are also associated with increased mortality.

Medical Care

Surgical Care

Consultations

Diet

Activity

Medication Summary

Medications are best used for specific diagnoses. However, corticosteroids, cytotoxic agents, and, more recently, antifibrotics, antioxidants, and other immunosuppressive agents have been used with varying success in some forms of DPLD.

In general, NSIP, DIP, and COP have been found to be more responsive to corticosteroids and immunosuppressive therapies. UIP is generally thought to be unresponsive to these modalities, and thus, additional research in the form of clinical trials evaluating potentially promising agents continues. RBILD responds to smoking cessation.

Prednisone (Sterapred)

Clinical Context:  Used as immunosuppressant in treatment of autoimmune disorders. By reversing increased capillary permeability and suppressing PMN activity, may decrease inflammation. Oral corticosteroid with relatively less mineralocorticoid activity.

Best prescribed in consultation with a pulmonary disease specialist.

Class Summary

Have anti-inflammatory properties and cause profound and varied metabolic effects. In addition, modify body's immune response to diverse stimuli.

Cyclophosphamide (Cytoxan, Neosar)

Clinical Context:  Chemically related to nitrogen mustards. As an alkylating agent, mechanism of action of active metabolites may involve cross-linking of DNA, which may interfere with growth of normal and neoplastic cells of immune system. Possibly a steroid-sparing medication.

Azathioprine (Imuran)

Clinical Context:  Inhibits mitosis and cellular metabolism by antagonizing purine metabolism and inhibiting synthesis of DNA, RNA, and proteins. These effects may decrease proliferation of immune cells and result in lower autoimmune activity. Possibly a steroid-sparing medication.

Class Summary

Used for some of their immunosuppressant properties.

Colchicine

Clinical Context:  Decreases leukocyte motility and phagocytosis observed in inflammatory responses.

Class Summary

Immunosuppressive effects may inhibit cellular division and fibrosis.

Further Inpatient Care

Further Outpatient Care

Inpatient & Outpatient Medications

Transfer

Deterrence/Prevention

Complications

Prognosis

Author

Eleanor M Summerhill, MD, FACP, FCCP, Associate Professor of Medicine, Division of Pulmonary and Critical Care Medicine, Warren Alpert Medical School of Brown University; Director, Internal Medicine Residency Program, Memorial Hospital of Rhode Island

Disclosure: Nothing to disclose.

Specialty Editors

Stephen P Peters, MD, PhD, FACP, FAAAAI, FCCP, FCPP, Professor of Internal Medicine, Pediatrics, and Translational Science, Associate Director, Center for Genomics and Personalized Medicine Research, Director of Research, Section on Pulmonary, Critical Care, Allergy and Immunologic Diseases, Wake Forest University School of Medicine

Disclosure: See below for list of all activities None None

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Daniel R Ouellette, MD, FCCP, Associate Professor of Medicine, Wayne State University School of Medicine; Senior Academic Advisor, Pulmonary and Critical Care Fellowship Program, Henry Ford Hospital; Vice Chair, Health and Science Policy Committee, American College of Chest Physicians

Disclosure: Nothing to disclose.

Timothy D Rice, MD, Associate Professor, Departments of Internal Medicine and Pediatrics and Adolescent Medicine, St Louis University School of Medicine

Disclosure: Nothing to disclose.

Chief Editor

Zab Mosenifar, MD, Director, Division of Pulmonary and Critical Care Medicine, Director, Women's Guild Pulmonary Disease Institute, Professor and Executive Vice Chair, Department of Medicine, Cedars Sinai Medical Center, University of California, Los Angeles, David Geffen School of Medicine

Disclosure: Nothing to disclose.

Additional Contributors

The authors and editors of eMedicine gratefully acknowledge the contributions of previous author Robert S. Crausman, MD, MMS, to the development and writing of this article.

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Frontal chest radiograph demonstrating bilateral reticular and nodular interstitial infiltrates with upper zone predominance.

Frontal chest radiograph demonstrating bilateral reticular and nodular interstitial infiltrates with upper zone predominance.

High-resolution chest CT scan of patient with bilateral reticular and nodular interstitial infiltrates with upper zone predominance.

Frontal chest radiograph demonstrating bilateral reticular and nodular interstitial infiltrates with upper zone predominance.

High-resolution chest CT scan of patient with bilateral reticular and nodular interstitial infiltrates with upper zone predominance.