Review
Does Chronic Microaspiration Cause Idiopathic Pulmonary Fibrosis?

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Abstract

Idiopathic pulmonary fibrosis is a diffuse fibrotic lung disease of unknown etiology with no effective treatment. Emerging data support a role for chronic microaspiration (ie, subclinical aspiration of small droplets) in the pathogenesis and natural history of idiopathic pulmonary fibrosis. However, the precise relationship between chronic microaspiration and idiopathic pulmonary fibrosis remains unknown. Gastroesophageal reflux, a presumed risk factor for microaspiration, has been strongly associated with idiopathic pulmonary fibrosis with an estimated prevalence of up to 90%. This review aims to describe the relationship between chronic microaspiration and idiopathic pulmonary fibrosis by laying out the clinical and biologic rationale for this relationship and exploring the scientific evidence available. The gaps in our current understanding of the diagnosis of chronic microaspiration and idiopathic pulmonary fibrosis and the ongoing uncertainties in management and treatment will be highlighted. Defining the role of chronic microaspiration in idiopathic pulmonary fibrosis is essential as it has potential clinical, pathobiological, and treatment implications for this deadly disease.

Section snippets

Silent Microaspiration and Lung Disease

Aspiration is defined as the inhalation of oropharyngeal or gastric contents into the larynx and lower respiratory tract.6 The clinical syndrome due to aspiration (eg, aspiration pneumonitis, aspiration pneumonia) depends on the nature and volume of aspirated material, the frequency of aspiration, and the host's response to the aspirated material.

The term “silent” microaspiration is used when patients have asymptomatic aspiration of small volumes of oropharyngeal secretions or gastric fluid

Silent Microaspiration and Pulmonary Fibrosis

Evidence from experimental models in animals and descriptive studies in humans support the concept of microaspiration as a potential cause of pulmonary fibrosis.

Silent Microaspiration and Idiopathic Pulmonary Fibrosis

The above animal and human data support the concept of silent microaspiration leading to pulmonary fibrosis, but many questions remain. Perhaps the most significant is how to reconcile the observed histopathology of aspiration-related lung injury (ie, airways injury and granulomatous inflammation) with that of idiopathic pulmonary fibrosis (ie, usual interstitial pneumonia pattern).

Usual interstitial pneumonia pattern is characterized by histologic heterogeneity of fibrosis, with alternating

Making the Diagnosis of Microaspiration

Several approaches for diagnosing microaspiration have been suggested, each having its own set of advantages and disadvantages (Table). We describe a few of these methods below.

Clinical Management

Until further evidence is available, we cannot recommend a specific screening, diagnostic, or management algorithm for microaspiration in idiopathic pulmonary fibrosis. Much has been written about the need to screen and treat gastroesophageal reflux in this population.59, 60 However, there is equipoise in the idiopathic pulmonary fibrosis community as to how aggressively to pursue this diagnosis. Even within this group of authors, there are differences in practice patterns. This is primarily

Gaps in Knowledge

One possible mechanism of microaspiration leading to pulmonary fibrosis is illustrated in the Figure. However, many questions need to be addressed in future studies to clarify the role of silent microaspiration in patients with idiopathic pulmonary fibrosis:

  • What is the true prevalence of microaspiration in patients with idiopathic pulmonary fibrosis? The finding of gastroesophageal reflux does not imply microaspiration, and there is no consensus on a gold standard for the diagnosis of

Conclusion

The data summarized in this review are provocative and implicate a potential role for microaspiration in the etiology and natural history of idiopathic pulmonary fibrosis. We firmly believe that defining the precise relationship between microaspiration and idiopathic pulmonary fibrosis is critically important because of its potential pathobiological and therapeutic implications. In general, current treatment strategies in idiopathic pulmonary fibrosis have focused on modulating the fibrotic

Acknowledgment

The authors wish to thank Simon Kimm, MD, for illustrating the Figure.

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  • Cited by (0)

    Funding: NHLBI HL086516.

    Conflict of Interest: Dr. Lee has no conflicts of interest to disclose. Dr. Collard has provided consulting services to Actelion, Amira, InterMune, Gilead Science, Genzyme, CV Therapeutics, Nektar Therapeutics, and Roche, has served on an advisory committee for InterMune, and speaks regularly about idiopathic pulmonary fibrosis. Dr. Raghu has given lectures on the diagnosis and management of interstitial lung diseases and has discussed the potential role of chronic silent microaspiration in the pathogenesis of idiopathic pulmonary fibrosis. Dr. Sweet has no conflicts of interest to disclose. Dr. Hays has no conflicts of interest to disclose. Dr. Campos has no conflicts of interest to disclose. Dr. Golden has no conflicts of interest to disclose. Dr. King has given lectures on the diagnosis and management of interstitial lung diseases and has discussed the recent papers that have discussed the potential role of chronic silent microaspiration in the pathogenesis of idiopathic pulmonary fibrosis and as a potential cause of the acute respiratory decompensation manifested by some patients with idiopathic pulmonary fibrosis. In 2007, Dr. King provided expert testimony that a patient's diffuse parenchymal lung disease (lung fibrosis) was, more likely than not, caused by chronic aspiration.

    Authorship: This manuscript represents original work, and all authors meet the criteria for authorship.

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