Pulmonary fibrosis

Pulmonary fibrosis is a chronic and progressive lung disease characterized by the thickening and scarring of lung tissue, which impairs the lungs' ability to transfer oxygen into the bloodstream and makes breathing increasingly difficult over time.^[1] This condition falls under the broader category of interstitial lung diseases and can vary in progression, with some cases remaining stable while others advance rapidly, ultimately leading to respiratory failure if untreated.^[2] The causes of pulmonary fibrosis are diverse and often multifactorial, though in many instances, particularly idiopathic pulmonary fibrosis (IPF), the exact trigger remains unknown.^[3] Known causes include long-term exposure to environmental toxins such as silica dust, asbestos, or metal dusts in occupational settings like mining or farming; certain medications including chemotherapy drugs and heart medications like amiodarone; radiation therapy to the chest; and underlying medical conditions such as autoimmune diseases (e.g., rheumatoid arthritis or scleroderma) or gastroesophageal reflux disease (GERD).^[1] Risk factors encompass older age (typically affecting individuals over 50), male sex, cigarette smoking, a family history of the disease, and genetic predispositions in some cases.^[4] Complications may include pulmonary hypertension, right-sided heart failure (cor pulmonale), increased susceptibility to lung infections, and a higher risk of lung cancer.^[1] Symptoms of pulmonary fibrosis typically develop gradually and include persistent dry cough, shortness of breath (dyspnea) that worsens with physical activity, fatigue, unexplained weight loss, aching muscles and joints, and widening and rounding of the fingertips or toes (clubbing).^[5] In advanced stages, patients may experience acute exacerbations—sudden worsenings of symptoms that can be life-threatening—and reduced exercise tolerance due to decreased lung capacity.^[3] Diagnosis generally involves a combination of medical history review, physical examination, imaging such as high-resolution CT scans to visualize scarring patterns, pulmonary function tests to assess lung capacity and gas exchange, and sometimes lung biopsy to confirm the extent of fibrosis.^[6] While there is no cure for pulmonary fibrosis, treatments focus on slowing disease progression, relieving symptoms, and improving quality of life.^[2] Antifibrotic medications such as pirfenidone (Esbriet) and nintedanib (Ofev) are FDA-approved for IPF and certain other forms, reducing the rate of lung function decline but potentially causing side effects like nausea, diarrhea, or rash.^[6] Oxygen therapy helps maintain adequate blood oxygen levels, pulmonary rehabilitation programs enhance physical endurance through exercise and education, and lung transplantation may be considered for eligible patients with end-stage disease, though it carries risks of rejection and infection.^[6] Lifestyle modifications, including smoking cessation, avoiding lung irritants, vaccinations against respiratory infections, and a balanced diet, play a crucial role in management.^[7] Ongoing research continues to explore novel therapies targeting the underlying fibrotic processes.^[8]

Overview

Definition

Pulmonary fibrosis is a chronic, progressive lung disease characterized by the formation of scar tissue, or fibrosis, within the lungs, leading to stiffening of the lung tissue, reduced elasticity, and impaired gas exchange between the air and the bloodstream.^[1] This scarring disrupts the normal architecture of the lungs, making it difficult for them to expand fully during inhalation and to transfer oxygen effectively into the blood.^[3] The condition encompasses a group of disorders under the broader category of interstitial lung diseases, where the primary pathological feature is the excessive deposition of extracellular matrix components, such as collagen, in the lung parenchyma.^[9] In pulmonary fibrosis, the normal functional lung tissue is gradually replaced by dense, fibrous connective tissue, resulting in a restrictive ventilatory defect and progressive hypoxemia.^[10] This replacement process thickens the walls of the air sacs (alveoli) and the surrounding interstitial spaces, diminishing the lungs' capacity to hold air and facilitate efficient respiration.^[11] The fibrosis predominantly involves the interstitium—the supportive framework around the alveoli—and the alveoli themselves, with a characteristic distribution in the lower lobes of both lungs, though patterns can vary.^[1] Over time, these changes can advance to severe respiratory insufficiency if untreated.^[3] The condition was alluded to in the late 19th century under terms like "chronic pneumonitis," with fibrotic processes noted in autopsy findings. The acute, fulminant form of diffuse interstitial fibrosis was first detailed clinically and pathologically by Louis Hamman and Arnold Rich in 1944, based on cases from the preceding decade. Systematic understanding of the chronic progressive form developed later, with advancements in histopathology in the 1960s leading to formalized classifications by Avery A. Liebow and colleagues. These categorized idiopathic pulmonary fibrosis and related patterns, such as usual interstitial pneumonia, distinguishing the chronic disorder from acute and inflammatory lung conditions.^[12]^[13]

Classification

Pulmonary fibrosis is primarily classified into idiopathic and secondary forms based on etiology. Idiopathic pulmonary fibrosis (IPF) represents the most common type, characterized by progressive lung scarring of unknown cause, accounting for approximately 50% of idiopathic interstitial pneumonias.^[14] In contrast, secondary pulmonary fibrosis arises from identifiable triggers, allowing for targeted interventions in many cases.^[15] Secondary pulmonary fibrosis encompasses several subtypes. Familial pulmonary fibrosis, defined by a genetic predisposition and family history in affected relatives, accounts for up to 20% of IPF cases.^[16]^[14] Environmental and occupational exposures lead to conditions such as asbestosis from asbestos inhalation or silicosis from silica dust, often presenting with distinct radiographic patterns.^[15] Drug-induced fibrosis results from medications like amiodarone, chemotherapy agents, or certain antibiotics, typically resolving upon discontinuation if detected early.^[14] Connective tissue disease-associated fibrosis is linked to autoimmune disorders, such as scleroderma or rheumatoid arthritis, affecting about 15% of patients with these conditions.^[15] Hypersensitivity pneumonitis arises from repeated inhalation of organic antigens, like mold or bird proteins, leading to an allergic inflammatory response.^[14] Radiation-induced fibrosis develops following chest radiotherapy, often as a delayed complication in cancer survivors.^[15] An emerging category is post-infectious pulmonary fibrosis, particularly following severe viral infections such as COVID-19, where lung scarring persists as a sequela in a subset of patients, potentially non-progressive but impacting long-term function.^[15]^[17] In 2025, the international multidisciplinary classification of the idiopathic interstitial pneumonias was updated by the American Thoracic Society, European Respiratory Society, and Japanese Respiratory Society to incorporate advances in subtype definitions and diagnostic criteria.^[18] This classification guides diagnostic evaluation, prognosis, and management; for instance, IPF carries a median survival of 3–5 years without treatment and responds to antifibrotic therapies like pirfenidone or nintedanib, whereas secondary forms may improve with removal of the inciting agent or treatment of the underlying condition, potentially altering disease trajectory.^[14]^[15]

Clinical Presentation

Signs and Symptoms

Pulmonary fibrosis typically presents with progressive dyspnea on exertion as the most common initial symptom, which worsens over time and may eventually occur at rest.^[1]^[5]^[19] A persistent, non-productive dry cough is also frequent, often accompanied by fatigue and gradual unintended weight loss.^[1]^[20]^[5] In advanced stages, patients may develop cyanosis, manifesting as bluish discoloration of the skin around the mouth or fingernails due to chronic hypoxia.^[21]^[22] On physical examination, fine inspiratory crackles, often described as Velcro-like, are characteristically heard at the lung bases during auscultation.^[19] Digital clubbing, involving widening and rounding of the fingertips, occurs in approximately 25-50% of cases of idiopathic pulmonary fibrosis.^[23]^[24] Reduced chest expansion may also be noted due to stiffening of the lung tissue.^[1] The onset of symptoms is usually insidious, developing gradually over months to years, though diagnosis is often delayed by more than a year after initial presentation.^[19] Acute exacerbations can cause sudden deterioration, with rapid worsening of dyspnea over days to weeks, leading to significant respiratory distress.^[1]^[25] These manifestations substantially impair quality of life, primarily through reduced exercise tolerance and progressive limitation in daily activities.^[19] Sleep disturbances may arise from orthopnea, exacerbating fatigue and overall unwellness.^[20] Worsening dyspnea can sometimes reflect associated complications such as pulmonary hypertension.^[5]

Complications

Pulmonary fibrosis predisposes patients to several respiratory complications that can rapidly worsen disease progression. Acute exacerbations, characterized by sudden worsening of dyspnea and the appearance of new ground-glass opacities or infiltrates on imaging, represent a critical event often leading to acute respiratory distress syndrome and requiring mechanical ventilation.^[26] These episodes are frequently idiopathic but may be triggered by infections or other stressors, contributing to high short-term mortality rates.^[27] Secondary infections, such as pneumonia, are common due to impaired lung defenses and structural changes, increasing susceptibility to bacterial, viral, and fungal pathogens.^[28] Cardiovascular complications arise from the chronic strain on the pulmonary vasculature and right heart. Pulmonary hypertension develops in approximately 30-50% of patients with idiopathic pulmonary fibrosis, driven by vascular remodeling, hypoxic vasoconstriction, and loss of vascular bed surface area.^[29] This can progress to right heart failure, or cor pulmonale, exacerbating symptoms like worsening dyspnea through reduced cardiac output.^[30] Additionally, patients face an elevated risk of venous thromboembolism, with studies reporting a relative risk up to 2.11 compared to the general population, potentially due to immobility, inflammation, and prothrombotic states.^[31] Beyond respiratory and cardiovascular effects, pulmonary fibrosis leads to various systemic issues stemming from chronic hypoxemia and disease burden. Persistent low oxygen levels may rarely trigger secondary polycythemia as a compensatory increase in red blood cell production, though this response is uncommon in idiopathic pulmonary fibrosis despite frequent hypoxemia.^[32] Immobility and corticosteroid use contribute to osteoporosis, with observational data showing a significant association between pulmonary fibrosis and reduced bone mineral density in older adults.^[33] The chronic nature of the illness also heightens the risk of depression and anxiety, affecting nearly 46% of patients and impacting quality of life.^[34] These complications substantially drive morbidity and mortality in advanced pulmonary fibrosis. Acute exacerbations alone precede approximately 46% of deaths in idiopathic pulmonary fibrosis, while pulmonary hypertension and infections further accelerate decline, underscoring the need for vigilant monitoring and preventive strategies.^[35]

Etiology

Causes

Pulmonary fibrosis encompasses both idiopathic and secondary forms, with the latter arising from identifiable initiating factors that trigger chronic lung injury and aberrant repair processes. In idiopathic pulmonary fibrosis (IPF), the most common type, the etiology remains unknown, though it is hypothesized to stem from repeated subclinical alveolar epithelial injuries leading to dysregulated wound healing and progressive fibrosis.^[19] This form accounts for a significant proportion of cases without clear precipitating events.^[36] Environmental and occupational exposures represent major causes of secondary pulmonary fibrosis by inducing persistent inflammation through inhaled particles. Inhalation of inorganic dusts such as silica and asbestos, metal dusts from mining or welding, and organic antigens like those in moldy hay (causing hypersensitivity pneumonitis) or bird droppings can initiate chronic alveolar damage and fibrotic remodeling.^[36] For instance, prolonged exposure to asbestos fibers is a well-established trigger for asbestosis, a fibrotic lung disease.^[9] Iatrogenic factors, including certain medications and radiation therapy, directly contribute to fibrotic lung injury as unintended consequences of treatment. Chemotherapeutic agents like bleomycin and antibiotics such as nitrofurantoin are known to provoke oxidative stress and inflammation, culminating in pulmonary fibrosis in susceptible individuals.^[19] Chest radiation, commonly administered for thoracic malignancies, induces dose-dependent endothelial and epithelial damage that progresses to fibrosis, with higher radiation doses elevating the risk.^[36] Autoimmune diseases and infections serve as key triggers for pulmonary fibrosis by promoting systemic or localized inflammatory cascades. Connective tissue disorders, including rheumatoid arthritis and systemic sclerosis, frequently manifest with interstitial lung fibrosis due to autoimmune-mediated vascular and parenchymal injury.^[9] Infectious etiologies, such as severe SARS-CoV-2 infection, can lead to post-viral fibrosis through acute respiratory distress syndrome and unresolved inflammation, as observed in post-COVID-19 cases.^[37] Across secondary forms, a dose-response relationship often exists, wherein greater intensity or duration of exposure to environmental agents, medications, or radiation correlates with heightened fibrosis risk and severity.^[36] Genetic susceptibility can amplify these environmental triggers, though details are explored elsewhere.^[19]

Risk Factors

Pulmonary fibrosis, particularly its idiopathic form (IPF), is influenced by several demographic risk factors that predispose certain populations to higher susceptibility. The disease predominantly affects older adults, with peak incidence occurring after the age of 50 years, as the majority of diagnosed cases involve individuals in this age group.^[4] IPF is approximately 1.5 to 2 times more prevalent in men than in women, reflecting a sex-based disparity in disease occurrence.^[4] Additionally, higher reported rates are observed among Caucasian individuals compared to other ethnic groups, such as Black or Hispanic populations, where incidence appears lower.^[38] Behavioral factors play a significant role in elevating the risk of developing pulmonary fibrosis. Cigarette smoking is a well-established risk factor for IPF, with ever-smokers facing odds ratios of 1.5 to 2.0 compared to never-smokers, effectively doubling the risk in some analyses.^[39] Occupational exposures further contribute to susceptibility, particularly in industries involving inhalation of irritants; for instance, farming and mining are associated with increased risk due to chronic exposure to organic dusts, metal dusts, wood dusts, and silica.^[40] Certain comorbidities modify the risk profile for pulmonary fibrosis by potentially exacerbating lung injury or inflammation. Gastroesophageal reflux disease (GERD) is highly prevalent among IPF patients, affecting 40-90% of cases and serving as a key modifier through mechanisms like microaspiration.^[41] Obesity has been identified as an important risk factor, with higher body mass index linked to increased IPF incidence, possibly via systemic inflammation.^[42] Similarly, obstructive sleep apnea acts as a comorbidity that heightens susceptibility, with prevalence rates up to 88% in IPF cohorts, contributing to repetitive hypoxemia and lung stress.^[43] Familial clustering underscores a heritable predisposition, with 2-20% of IPF cases showing a family history of the disease, representing the strongest known risk factor and elevating odds up to sixfold in affected relatives.^[44]

Pathogenesis

Pathophysiological Mechanisms

Pulmonary fibrosis arises from a dysregulated injury-repair cycle in the lung parenchyma, where repeated injury to alveolar epithelial cells, particularly type II pneumocytes, initiates aberrant wound healing processes. This injury disrupts the alveolar-capillary barrier, leading to interstitial edema and activation of fibroblasts, which fail to resolve normally and instead perpetuate tissue remodeling.^[36] The cycle is characterized by ongoing epithelial damage that triggers a maladaptive repair response, shifting from resolution to progressive fibrosis.^[45] Inflammation plays a pivotal role in the early stages, with an influx of macrophages and neutrophils responding to epithelial injury by releasing pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-13. These cells transition the response from an acute inflammatory phase to a fibroproliferative one, where alternatively activated macrophages (M2 phenotype) further amplify fibrosis through sustained cytokine production and recruitment of additional immune cells.^[36] This inflammatory milieu promotes fibroblast proliferation and differentiation into myofibroblasts, marking the onset of the fibrotic cascade.^[46] The fibrotic cascade involves the differentiation of fibroblasts into alpha-smooth muscle actin-expressing myofibroblasts, which excessively deposit extracellular matrix (ECM) components, including collagen types I and III, leading to scar tissue formation and lung stiffening. Myofibroblasts exhibit resistance to apoptosis, prolonging ECM accumulation and preventing the natural resolution of repair.^[36] Key profibrotic signals, such as TGF-β, drive this process by stimulating myofibroblast activation and ECM synthesis, though detailed molecular pathways are elaborated elsewhere.^[46] Vascular alterations contribute to disease progression through endothelial dysfunction, which impairs vascular integrity and promotes hypoxia in the fibrotic lung tissue. This hypoxia exacerbates epithelial injury and stimulates further myofibroblast activity, creating a vicious cycle that sustains fibrosis via angiogenic factors and reduced oxygen delivery.^[36] Animal models, particularly bleomycin-induced pulmonary fibrosis in mice and hamsters, recapitulate these mechanisms by inducing initial epithelial damage, inflammatory cell infiltration, and subsequent collagen deposition, serving as a standard for investigating fibrotic progression and potential interventions.^[36]

Genetic and Molecular Factors

Pulmonary fibrosis, particularly idiopathic pulmonary fibrosis (IPF), exhibits a significant genetic component, with specific mutations and variants influencing disease susceptibility and progression. Mutations in the telomerase reverse transcriptase (TERT) and telomerase RNA component (TERC) genes, which are critical for telomere maintenance, are implicated in approximately 15% of familial IPF cases.^[47] These heterozygous mutations lead to telomere shortening, predisposing individuals to premature cellular senescence and fibrotic lung remodeling. In sporadic IPF, the prevalence of TERT and TERC mutations is lower, around 1-3%, but they still contribute to disease heterogeneity.^[48] Additionally, the promoter variant in the MUC5B gene (rs35705950) serves as the strongest known genetic risk factor, with the minor T allele frequency of approximately 30-40% in sporadic IPF cases, particularly in populations of European ancestry, enhancing mucin production and altering alveolar homeostasis to favor fibrosis.^[49] At the molecular level, transforming growth factor-β (TGF-β) signaling represents a central profibrotic pathway in pulmonary fibrosis, driving the differentiation of fibroblasts into myofibroblasts and excessive production of extracellular matrix (ECM) components such as collagen and fibronectin.^[50] TGF-β activates Smad-dependent transcription factors that upregulate ECM genes, while also promoting epithelial-mesenchymal transition in alveolar cells, thereby perpetuating fibrotic scarring. Connective tissue growth factor (CTGF), often induced downstream of TGF-β, amplifies these effects by enhancing fibroblast proliferation and ECM deposition, with elevated CTGF levels observed in IPF lung tissue.^[51] Similarly, platelet-derived growth factor (PDGF) isoforms, particularly PDGF-BB, stimulate fibroblast chemotaxis and proliferation through PDGF receptor tyrosine kinases, contributing to the accumulation of mesenchymal cells in fibrotic lesions.^[52] Epigenetic alterations further modulate fibrosis susceptibility, including dysregulation of microRNAs (miRNAs) that fine-tune gene expression. Downregulation of miR-29, a key antifibrotic miRNA, is consistently observed in IPF lungs, leading to derepression of ECM genes like collagen type I alpha 1 (COL1A1) and elastin, which exacerbates matrix accumulation.^[53] Telomere shortening, often linked to TERT/TERC defects, accelerates alveolar epithelial cell senescence, characterized by β-galactosidase activity and p16/p21 upregulation, creating a profibrotic microenvironment through the senescence-associated secretory phenotype.^[54] Recent studies have highlighted the role of SWI/SNF chromatin remodeling complexes in epigenetic regulation of pulmonary fibrosis, with 2024 research demonstrating that the Brg1 subunit (SMARCA4) forms a nuclear complex with PRMT5 to epigenetically silence FOXO1 in IPF myofibroblasts, promoting their persistence and fibrotic gene expression.^[55] This complex alters chromatin accessibility at antifibrotic loci, offering insights into novel therapeutic targets for disrupting epigenetic drivers of disease progression.^[56] A 2025 study has further elucidated the role of persistent hypoxia-inducible factor (HIF) signaling, particularly HIF2α, in aberrant alveolar epithelial cells as a driver of IPF progression. This sustained activation promotes the emergence of abnormal cells and impairs alveolar repair, exacerbating fibrosis. Preclinical models demonstrate that HIF2α inhibition reduces fibrotic changes and enhances repair, identifying this pathway as a promising molecular target.^[57]

Diagnosis

History and Physical Examination

The history and physical examination serve as the initial steps in suspecting pulmonary fibrosis, guiding clinicians to identify suggestive features and exclude alternative diagnoses. Patients typically present with a gradual onset of exertional dyspnea, often progressing over months to years, which is the most common symptom prompting evaluation.^[19] A thorough inquiry into cough characteristics reveals it as dry and nonproductive in the majority of cases, frequently accompanying dyspnea without association with infections or allergens.^[58] Occupational and environmental exposures must be explored, including prolonged contact with inorganic dusts (e.g., silica or asbestos), metals, mold, or avian antigens, as these may indicate hypersensitivity pneumonitis or other interstitial lung diseases rather than idiopathic forms.^[19] Family history is critical, with questions about relatives with premature aging signs, early-onset lung disease, or known familial pulmonary fibrosis, given that up to 5% of cases have a genetic component.^[58] Comorbidities such as gastroesophageal reflux disease (GERD; objective prevalence up to 90%, symptomatic in ~30-50% of patients), coronary artery disease, hypothyroidism, or connective tissue disorders should be assessed, as they may contribute to or mimic fibrotic processes.^[19]^[59] On physical examination, auscultation of the lungs is paramount, revealing fine, bibasilar "Velcro-like" inspiratory crackles in most patients, which are dry and end-inspiratory, distinguishing them from the coarser crackles of heart failure.^[58] Digital clubbing is observed in 25-50% of cases, particularly in advanced idiopathic pulmonary fibrosis, while cyanosis may appear in severe disease with resting hypoxemia.^[19] Vital signs assessment includes measuring respiratory rate, which may be elevated due to compensatory tachypnea, and pulse oximetry to detect oxygen desaturation, often subtle at rest but worsening with exertion.^[6] The absence of wheezing or rhonchi helps differentiate from obstructive airway diseases like asthma or chronic obstructive pulmonary disease.^[19] Red flags during evaluation include progressive dyspnea without a history of smoking-related lung disease or asthma, raising suspicion for fibrotic etiology over obstructive conditions. Unintentional weight loss, fatigue, or systemic symptoms like joint pain and skin rashes may signal underlying connective tissue disease or malignancy mimicking fibrosis, necessitating further scrutiny of exposures and family history to refine the differential.^[58]

Imaging and Laboratory Tests

High-resolution computed tomography (HRCT) serves as the gold standard imaging modality for diagnosing pulmonary fibrosis, particularly in identifying the usual interstitial pneumonia (UIP) pattern characterized by subpleural and basal predominant reticular opacities, honeycombing, and traction bronchiectasis.^[60] This pattern on HRCT has a high positive predictive value (90-100%) for confirming UIP in idiopathic pulmonary fibrosis (IPF), often obviating the need for biopsy when clinical context aligns. Per the 2022 ATS/ERS/JRS/ALAT guidelines, in patients with newly detected interstitial lung disease of unknown cause and a probable UIP pattern on HRCT, IPF may be diagnosed without biopsy after multidisciplinary team (MDT) discussion.^[61] Chest X-ray is used for initial screening, typically revealing bilateral reticular opacities and lower lobe volume loss, though it lacks specificity and sensitivity compared to HRCT.^[62] Pulmonary function tests (PFTs) demonstrate a restrictive ventilatory pattern in pulmonary fibrosis, with reduced forced vital capacity (FVC typically <80% predicted) and decreased diffusing capacity for carbon monoxide (DLCO often <40% predicted), reflecting impaired lung compliance and gas exchange.^[62] These tests are essential for confirming the diagnosis and assessing disease severity, showing progressive declines that correlate with fibrosis extent. Diagnosis of IPF and other forms of pulmonary fibrosis requires integration of findings by a multidisciplinary team, including pulmonologists, radiologists, and pathologists. No specific laboratory blood test exists for diagnosing pulmonary fibrosis, but serological testing for connective tissue diseases is recommended to exclude alternative etiologies, including antinuclear antibody (ANA), rheumatoid factor (RF), and myositis-specific antibodies.^[60] The 6-minute walk test (6MWT) evaluates functional status by measuring exercise tolerance and oxygen desaturation, with desaturation below 88% indicating significant impairment.^[63] In cases of indeterminate or inconsistent HRCT patterns, invasive surgical lung biopsy via video-assisted thoracoscopic surgery is performed for definitive histopathological confirmation of UIP, though it carries risks such as prolonged air leak (up to 20%) and mortality (1-5%).^[60]^[64] Transbronchial lung cryobiopsy is an emerging alternative in experienced centers, offering a diagnostic yield of approximately 80% with lower complication rates.^[65] The GAP index, incorporating gender (male: 2 points, female: 0), age (>65 years: 2 points, ≤65 years: 0), FVC % predicted (>75%: 0 points, 50-75%: 1 point, <50%: 2 points), and DLCO % predicted (>55%: 0 points, 36-55%: 1 point, ≤35%: 2 points), stages disease severity into I (0-3 points), II (4-5 points), or III (6-8 points) for risk stratification in IPF.^[66] This simple tool uses routinely available data to predict 1-, 2-, and 3-year mortality, aiding in diagnostic and management planning.

Treatment

Pharmacological Therapies

Pharmacological therapies for pulmonary fibrosis primarily aim to slow disease progression and alleviate symptoms, with antifibrotic agents forming the cornerstone of treatment for idiopathic pulmonary fibrosis (IPF). These medications target fibrotic pathways to preserve lung function, as measured by forced vital capacity (FVC), without reversing existing damage. Two antifibrotics, pirfenidone and nintedanib, are widely used and approved by the U.S. Food and Drug Administration (FDA) in 2014 for IPF in adults. Pirfenidone, an oral pyridone derivative, reduces the decline in FVC by approximately 50% over 52 weeks compared to placebo, as demonstrated in the phase 3 ASCEND trial, and also improves progression-free survival. Nintedanib, a small-molecule tyrosine kinase inhibitor targeting receptors involved in fibrogenesis such as platelet-derived growth factor receptor (PDGFR), vascular endothelial growth factor receptor (VEGFR), and fibroblast growth factor receptor (FGFR), slows FVC decline by about 33% and reduces the risk of acute exacerbations. Both drugs are recommended for patients with mild to moderate IPF based on guidelines from the American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and Latin American Thoracic Association. Common side effects include gastrointestinal (GI) disturbances, such as nausea, diarrhea, and weight loss, with pirfenidone additionally causing photosensitivity and requiring liver function monitoring due to rare hepatotoxicity; nintedanib often leads to more pronounced diarrhea, manageable with dose adjustments or antidiarrheal agents. In October 2025, the FDA approved nerandomilast (JASCAYD), a selective phosphodiesterase-4B (PDE4B) inhibitor, as the first new IPF therapy in over a decade, based on the phase 3 FIBRONEER-IPF trial. This oral medication, dosed at 9 mg or 18 mg twice daily, resulted in a smaller FVC decline over 52 weeks compared to placebo (least squares mean difference of 68.8 mL for the higher dose), with benefits observed across subgroups including those on background antifibrotics.^[67] Nerandomilast modulates inflammation and fibrosis by elevating cyclic adenosine monophosphate (cAMP) levels, potentially offering additive effects when combined with pirfenidone or nintedanib. Its side effect profile includes mild to moderate GI upset and headache, with ongoing monitoring for psychiatric effects typical of PDE4 inhibitors. Emerging therapies include taladegib (ENV-101), a hedgehog pathway inhibitor granted orphan drug designation by the FDA and European Commission in July 2025 and Priority Medicines (PRIME) designation by the European Medicines Agency in November 2025 for IPF treatment.^[68] This investigational oral agent targets smoothened (SMO) to disrupt fibrogenic signaling, with phase 2b trials (WHISTLE-PF) ongoing and expected to complete enrollment by 2026. For symptom management, antacids such as proton pump inhibitors (PPIs) are commonly prescribed to address gastroesophageal reflux disease (GERD), which affects up to 90% of IPF patients and may exacerbate fibrosis through microaspiration, though evidence for direct disease-modifying effects remains limited. In inflammatory subtypes like hypersensitivity pneumonitis with fibrotic features, corticosteroids (e.g., prednisone at 0.5-1 mg/kg/day) and immunosuppressants (e.g., azathioprine or mycophenolate mofetil) are used to reduce inflammation and slow progression, particularly in cases with significant lymphocytic infiltrates, with treatment durations of 4-8 weeks initially followed by taper. Experimental pharmacological approaches show promise in preclinical models. HIF-2α inhibitors, such as PT-2385, have demonstrated reduction in pulmonary fibrosis by promoting alveolar regeneration and attenuating epithelial remodeling in mouse models of repetitive lung injury, with 2025 studies highlighting enhanced maturation of alveolar cells in human lung organoids treated with the drug. TNIK inhibitors, targeting the Wnt/β-catenin pathway, represent another avenue; a 2024 preclinical study identified a small-molecule TNIK inhibitor that alleviated fibrosis in human precision-cut lung slices and bleomycin-induced mouse models by suppressing TGF-β and YAP/TAZ signaling, while a 2025 AI-discovered first-in-class agent (INS018_055) advanced to phase 2a trials for IPF. These investigational therapies underscore ongoing efforts to address unmet needs in progressive fibrosing interstitial lung diseases, with supportive oxygen therapy often integrated for symptom relief as detailed in non-pharmacological interventions.

Non-Pharmacological Interventions

Non-pharmacological interventions play a crucial role in managing pulmonary fibrosis by alleviating symptoms, enhancing functional capacity, and supporting overall quality of life, often integrated with pharmacological approaches to optimize patient outcomes. These strategies encompass oxygen supplementation, structured rehabilitation programs, surgical options like transplantation, preventive measures such as vaccinations, palliative symptom control, and targeted patient education to promote self-management.^[69] Oxygen therapy is recommended for patients with pulmonary fibrosis experiencing hypoxemia, typically defined as a partial pressure of arterial oxygen (PaO2) ≤55 mmHg or oxygen saturation (SpO2) ≤88% at rest, with long-term use of at least 15 hours per day to improve exercise tolerance and reduce dyspnea. According to American Thoracic Society (ATS) guidelines, this intervention enhances quality of life in hypoxemic individuals by maintaining adequate oxygenation during daily activities and exertion.^[70]^[71] Pulmonary rehabilitation involves multidisciplinary, structured exercise training programs lasting 6 to 12 weeks, which have been shown to increase six-minute walk distance by an average of 37 meters, thereby improving endurance, reducing breathlessness, and enhancing health-related quality of life in patients with pulmonary fibrosis. The ATS and European Respiratory Society (ERS) endorse these programs as a standard supportive measure, emphasizing aerobic and strength training tailored to individual tolerance levels, though access may be limited in certain regions.^[69]^[72] Lung transplantation represents the only potentially curative non-pharmacological option for eligible patients with advanced pulmonary fibrosis, with referral criteria including forced vital capacity (FVC) below 65% predicted, diffusing capacity for carbon monoxide (DLCO) below 35-40% predicted, or progressive decline despite optimal therapy, alongside absence of significant comorbidities and typically age under 65 years. The International Society for Heart and Lung Transplantation (ISHLT) guidelines outline these selection parameters to identify candidates likely to benefit from the procedure, focusing on those with end-stage disease. Vaccinations against influenza and pneumococcal infections are strongly advised for all patients with pulmonary fibrosis to mitigate the risk of acute exacerbations and respiratory complications, as per ATS and ERS recommendations. Annual influenza vaccination and the 23-valent pneumococcal polysaccharide vaccine (PPSV23) are prioritized, with evidence indicating reduced hospitalization rates from preventable infections in this vulnerable population.^[73]^[74] Palliative care interventions, including the use of low-dose opioids for refractory dyspnea in end-stage disease, are recommended by the ATS for integration throughout the disease course to alleviate symptom burden and improve comfort. These approaches, often involving opioids like morphine, have demonstrated effectiveness in reducing breathlessness intensity without accelerating disease progression.^[75]^[69] Patient education focuses on empowering individuals through strategies such as smoking cessation, which is essential given smoking's role as a modifiable risk factor, and fall prevention techniques to address mobility challenges associated with progressive dyspnea. Programs emphasize nutritional support, adherence to therapy, and early recognition of complications, with resources from organizations like the Pulmonary Fibrosis Foundation highlighting the benefits of quitting smoking to slow functional decline.^[76]^[6]

Prognosis

Survival and Progression

Pulmonary fibrosis is a progressive condition with variable survival outcomes depending on the underlying etiology. In idiopathic pulmonary fibrosis (IPF), the most common and severe form, the median survival from diagnosis is typically 3 to 5 years overall, with 2-3 years in untreated cases.^[77]^[78] Secondary forms of pulmonary fibrosis, such as those associated with connective tissue diseases or environmental exposures, often carry a better prognosis than IPF, with median survival varying by cause (e.g., 5-8 years for systemic sclerosis-associated interstitial lung disease), particularly when the causative factor is identified and removed early.^[79] Disease progression in pulmonary fibrosis is characterized by a gradual decline in lung function, primarily measured by forced vital capacity (FVC), at a rate of approximately 200-250 mL per year in untreated IPF patients.^[80] Acute exacerbations represent critical acceleration points, often leading to rapid deterioration and high mortality, with 30-50% of affected patients succumbing within 90 days and over 80% within one year of the event.^[81]^[82] These episodes underscore the unpredictable trajectory, where stable periods alternate with sudden worsening. Survival varies markedly by subtype. IPF exhibits the poorest outcomes. In contrast, post-COVID-19 pulmonary fibrosis often shows a more favorable course with improvement or resolution in many cases within one year (see Epidemiology for post-COVID-19 considerations).^[83] Secondary fibroses linked to treatable causes, such as hypersensitivity pneumonitis, also tend toward longer survival when interventions address the trigger.^[84] In end-stage pulmonary fibrosis, respiratory failure and acute exacerbations account for over 50% of deaths, often precipitated by progressive fibrosis or acute events.^[85] Hospice utilization among these patients has increased significantly in recent years, reflecting a shift toward supportive care in the terminal phase to manage symptoms and improve quality of life.^[86] With antifibrotic therapies, survival has improved in some cohorts, with median times exceeding 5 years.^[87]

Prognostic Factors

Several clinical factors influence the prognosis of pulmonary fibrosis, particularly in idiopathic pulmonary fibrosis (IPF). Desaturation during the 6-minute walk test (6MWT), defined as oxygen saturation ≤88%, is a significant predictor of mortality, with affected patients experiencing worse outcomes independent of other variables.^[88] A history of acute exacerbations further worsens prognosis, as these events are life-threatening and associated with a median survival of only 3-4 months post-exacerbation.^[89] Comorbidities, such as pulmonary hypertension, substantially impair survival; for instance, its presence can halve median survival time compared to IPF patients without this condition.^[90] Physiological parameters at baseline also serve as key prognostic indicators. Reduced forced vital capacity (FVC) below 70% predicted or diffusing capacity for carbon monoxide (DLCO) below 35% predicted signals advanced disease and correlates with shorter survival.^[91] The Gender-Age-Physiology (GAP) index, which combines gender, age, FVC, and DLCO into a score ranging from 0 to 8, stratifies risk effectively; stage III (scores >5) is linked to a 1-year mortality rate of approximately 40%.^[92] Biomarkers provide additional prognostic insights, especially for disease progression. Elevated serum levels of Krebs von den Lungen-6 (KL-6) or surfactant protein-D (SP-D) are associated with faster progression and poorer outcomes in IPF.^[93] In genetic cases, shorter telomere length independently predicts reduced transplant-free survival.^[94] Response to antifibrotic therapies, such as pirfenidone or nintedanib, can positively influence prognosis; stability or slower decline in FVC following treatment initiation is a favorable predictor of prolonged survival.^[95] Recent studies on post-COVID-19 pulmonary fibrosis indicate that cases with lower fibrosis severity scores on imaging exhibit higher rates of resolution, suggesting a potentially more reversible course compared to idiopathic forms (see Epidemiology for details).^[83]

Epidemiology

Incidence and Prevalence

Pulmonary fibrosis, including both idiopathic and secondary forms, affects more than 5 million individuals worldwide. Idiopathic pulmonary fibrosis (IPF), the most prevalent subtype, has a global incidence of approximately 3 to 9 cases per 100,000 person-years, with pooled estimates around 5.8 per 100,000. Prevalence varies regionally but is estimated at 14 to 63 cases per 100,000 in the United States and Europe based on 2023 data, reflecting differences in diagnostic criteria and population demographics.^[96]^[97]^[24] The condition disproportionately impacts certain demographics, with a male-to-female ratio of about 2:1, and approximately 90% of cases occurring in individuals over 50 years of age. Incidence and prevalence are notably higher among older adults, with mean diagnostic ages typically in the late 60s to early 70s. In regions like Asia and Africa, the disease is likely underreported due to limited access to advanced diagnostics such as high-resolution computed tomography and multidisciplinary evaluations.^[98]^[99]^[100] Epidemiological trends indicate a rising burden, attributed to aging populations and improved detection methods. In the United States, IPF prevalence among Medicare beneficiaries increased by over 140% from 202.2 cases per 100,000 in 2001 to 494.5 per 100,000 in 2011. Secondary forms constitute a significant portion.^[101]^[102]

Post-COVID-19 Considerations

Pulmonary fibrosis has emerged as a notable sequela following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, particularly in the context of the global COVID-19 pandemic that began in 2020. Meta-analyses from 2023 to 2025 indicate that 4-45% of survivors from severe COVID-19 cases develop pulmonary fibrosis, with higher rates observed in those requiring intensive care.^[103]^[104] Overall, the incidence of post-COVID-19 pulmonary fibrosis stands at approximately 4.37%, escalating to 8-20% among intensive care unit patients and those with severe disease manifestations.^[105] These findings underscore the condition's association with acute lung injury during the viral phase, often visualized on computed tomography (CT) scans as progression from ground-glass opacities to fibrotic changes.^[106] A distinguishing feature of post-COVID-19 pulmonary fibrosis is its frequently transient nature, contrasting with more progressive forms of the disease. According to a 2025 study from the University of South Florida Health, 50-70% of cases show resolution within 1-3 years, attributed to reversible inflammatory pathways rather than irreversible scarring.^[107] This evolution typically begins with diffuse alveolar damage leading to early fibrotic patterns, but many patients experience partial or complete regression without specific antifibrotic intervention.^[108] Key risk predictors for developing post-COVID-19 pulmonary fibrosis include the severity of the initial infection, need for mechanical ventilation, and advanced age. Patients hospitalized with critical illness face elevated odds, while vaccination status inversely correlates with risk, as immunized individuals tend to experience milder disease courses.^[109]^[110] These factors highlight the role of acute hypoxemia and prolonged inflammation in pathogenesis. In the long term, pulmonary fibrosis persists in 20-30% of affected individuals up to three years post-infection, contributing to symptoms of long COVID such as dyspnea and reduced exercise capacity.^[111] Unlike idiopathic pulmonary fibrosis, which is characteristically progressive and irreversible, post-COVID-19 cases often demonstrate potential for reversibility, offering insights into modifiable fibrotic mechanisms.^[112] The advent of COVID-19 has substantially increased the global burden of pulmonary fibrosis since 2020, with millions potentially affected due to the pandemic's scale. However, 2025 epidemiological updates reveal a declining incidence, linked to the emergence of milder SARS-CoV-2 variants and widespread vaccination efforts that attenuate severe respiratory outcomes.^[113]^[114] This trend suggests a stabilizing public health impact, though ongoing surveillance remains essential for managing residual cases.