Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive fibrosing interstitial pneumonia of unknown cause, occurring mainly in older adults and characterized by a usual interstitial pneumonia (UIP) pattern. It is the most common and one of the most lethal of the idiopathic interstitial pneumonias, defined in part by the absence of an identifiable cause or associated systemic disease.

Definition

Idiopathic pulmonary fibrosis is a specific form of chronic, progressive fibrosing interstitial pneumonia of unknown cause, limited to the lungs, associated with the histopathologic and/or radiologic pattern of usual interstitial pneumonia, and diagnosed by excluding other known causes of interstitial lung disease.

Scope

This entry covers the definition of IPF, the UIP pattern that anchors its diagnosis, its presumed pathogenesis of aberrant wound healing, and the multidisciplinary diagnostic approach that excludes other causes of fibrosis. It is a reference and educational overview and does not provide individualized diagnostic or treatment guidance.

Key concepts

• Usual interstitial pneumonia (UIP) pattern
• Diagnosis of exclusion
• Aberrant alveolar epithelial repair
• Fibroblast and myofibroblast activation
• Honeycombing and traction bronchiectasis on HRCT
• Multidisciplinary diagnosis
• Antifibrotic therapy concept
• Acute exacerbation of IPF

Mechanisms

The prevailing model holds that repetitive injury to aging alveolar epithelial cells, in a genetically and environmentally susceptible host, triggers dysregulated wound healing rather than inflammation as the primary driver. Injured epithelium releases profibrotic mediators that recruit and activate fibroblasts and myofibroblasts, which deposit excess extracellular matrix and form fibroblastic foci. The result is progressive, irreversible scarring with the spatially and temporally heterogeneous architecture of usual interstitial pneumonia, including honeycombing. This reconceptualization away from a chronic-inflammation model reshaped both diagnosis and the rationale for antifibrotic rather than anti-inflammatory strategies.

Clinical relevance

IPF illustrates how a fibrotic interstitial disease is distinguished from inflammatory mimics through integrated clinical, radiologic, and pathologic assessment, and it is the prototype against which other progressive-fibrosing ILDs are compared. This entry describes the disease for reference; it does not recommend specific tests or therapies for individuals, and treatment decisions belong to qualified clinicians.

Epidemiology

IPF typically presents in adults over 60, more often in men and in people with a history of cigarette smoking. It is the most frequent of the idiopathic interstitial pneumonias and historically carried a median survival of only a few years from diagnosis, although course is variable and can include episodes of acute deterioration.

Evidence & guidelines

The 2011 ATS/ERS/JRS/ALAT statement defined IPF and the UIP pattern and set out evidence-based diagnostic criteria, and the 2018 clinical practice guideline refined the radiologic and pathologic diagnostic categories. Randomized trials, including the nintedanib trials reported by Richeldi and colleagues in 2014, established that antifibrotic therapy can slow the decline in lung function, marking a shift from earlier anti-inflammatory approaches. These are cited as evidence landmarks, not as treatment instructions.

History

Long known under terms such as cryptogenic fibrosing alveolitis, IPF was progressively separated from other interstitial pneumonias as classifications matured. The recognition that the usual interstitial pneumonia pattern carried a distinct prognosis, and the later shift from an inflammation-centered to a fibrosis-centered model of pathogenesis, were pivotal; the 2011 international statement consolidated the modern definition and the 2018 guideline updated its diagnostic framework.

Debates

Is IPF primarily a disease of inflammation or of aberrant repair?

Earlier models framed IPF as chronic inflammation progressing to fibrosis, but accumulating evidence reframed it as dysregulated epithelial injury and wound healing with fibrosis as the central process, a shift that changed therapeutic rationale toward antifibrotic agents.

Key figures

• Ganesh Raghu
• Luca Richeldi
• Harold Collard
• David Lederer
• Fernando Martinez

Seminal works

• raghu-2011-atsers
• raghu-2018-diagnosis
• richeldi-2014-inpulsis

Frequently asked questions

What does "idiopathic" mean in idiopathic pulmonary fibrosis?

It means the cause is unknown: IPF is diagnosed only after other identifiable causes of fibrosis, such as connective tissue disease, drug toxicity, or environmental exposure, have been excluded.

What is the usual interstitial pneumonia (UIP) pattern?

UIP is the radiologic and pathologic pattern that anchors the diagnosis of IPF, marked by patchy, peripheral, basal-predominant fibrosis with honeycombing and a heterogeneous mix of scarred and relatively spared lung.