Idiopathic Pulmonary Fibrosis

Idiopathic Pulmonary Fibrosis
Name	Idiopathic Pulmonary Fibrosis
Field	Pulmonology
Symptoms	Dyspnea, Chronic cough
Complications	Pulmonary hypertension, Respiratory failure
Onset	Gradual
Duration	Chronic
Causes	Unknown
Risks	Cigarette smoking, Gastroesophageal reflux disease, Environmental exposure
Diagnosis	High-resolution computed tomography, Surgical lung biopsy
Differential	Hypersensitivity pneumonitis, Sarcoidosis, Connective tissue disease
Treatment	Antifibrotic therapy, Pulmonary rehabilitation, Lung transplantation
Medication	Pirfenidone, Nintedanib
Prognosis	Poor
Frequency	~3 million globally

Idiopathic Pulmonary Fibrosis is a chronic, progressive, and ultimately fatal Interstitial lung disease of unknown cause. It is characterized by the scarring, or Fibrosis, of the Lung tissue, which leads to a progressive decline in Lung function. The disease primarily affects older adults, with a median age at diagnosis of 66 years, and carries a prognosis worse than many cancers. Diagnosis requires the exclusion of other known causes of Interstitial lung disease, such as Connective tissue disease or Hypersensitivity pneumonitis.

Signs and symptoms

The most common presenting symptom is insidious onset Dyspnea (shortness of breath), particularly upon exertion, which patients often initially attribute to Aging or Deconditioning. A persistent, dry Chronic cough is also a frequent and troublesome feature. As the disease advances, patients may develop Digital clubbing of the fingers and toes. Upon Auscultation of the chest, clinicians often hear characteristic late-inspiratory crackles, known as "Velcro crackles." Advanced disease leads to Hypoxemia (low blood oxygen), initially with activity and later at rest, and may be complicated by Pulmonary hypertension and Cor pulmonale.

Causes and risk factors

By definition, the cause is unknown ("idiopathic"), but several strong epidemiological associations have been identified. The single greatest risk factor is a history of Cigarette smoking, which is present in the majority of patients. Chronic Gastroesophageal reflux disease (GERD) is also a common comorbidity, though its role as a causative agent versus a consequence of the disease is debated. Other potential risk factors include certain Environmental exposures, such as to metal or wood dust, and occupations like farming. There is also evidence for a genetic predisposition, with familial clustering observed and specific gene variants, such as in the MUC5B promoter, being strongly associated with disease development.

Pathophysiology

The prevailing hypothesis is that IPF results from repetitive, microscopic injury to the Alveolar epithelium in a susceptible aging individual. This injury triggers an aberrant repair response characterized by the activation and proliferation of Fibroblasts and their differentiation into Myofibroblast, which deposit excessive Extracellular matrix proteins like Collagen. This process, driven by complex signaling pathways involving Transforming growth factor beta (TGF-β), Platelet-derived growth factor (PDGF), and Fibroblast growth factor (FGF), leads to the destruction of the normal Lung architecture and the formation of Honeycomb lung.

Diagnosis

Diagnosis is based on a combination of clinical, radiological, and, in some cases, pathological criteria, following the exclusion of other Interstitial lung diseases. The cornerstone of diagnosis is High-resolution computed tomography (HRCT) of the chest. A definitive pattern of Usual interstitial pneumonia (UIP) on HRCT—showing subpleural and basal predominant Reticulation, Honeycombing, and an absence of features suggestive of alternative diagnoses—is sufficient for diagnosis without Biopsy. When the HRCT pattern is indeterminate, a Surgical lung biopsy performed via Video-assisted thoracoscopic surgery (VATS) may be required to obtain histopathological confirmation of UIP.

Treatment and management

Until the 2010s, treatment options were limited to supportive care and Lung transplantation. The approval of two antifibrotic agents, Pirfenidone and Nintedanib, has changed the therapeutic landscape, as both have been shown in large clinical trials like ASCEND and INPULSIS to slow the rate of Forced vital capacity decline. Supportive care is critical and includes Pulmonary rehabilitation, supplemental Oxygen therapy for hypoxemia, and management of comorbidities like GERD. For appropriate patients, Lung transplantation remains the only intervention that can prolong survival, with centers like Cleveland Clinic and Mayo Clinic having extensive experience.

Prognosis

The prognosis is poor, with a median survival of 3 to 5 years from diagnosis, though there is significant individual variability. Disease progression is measured by the decline in pulmonary function tests, particularly the Forced vital capacity (FVC) and Diffusing capacity for carbon monoxide (DLCO). Acute exacerbations, characterized by a rapid worsening of Dyspnea and new ground-glass opacities on HRCT, carry a very high mortality rate, often exceeding 50%. The leading cause of death is Respiratory failure, though complications such as Pulmonary hypertension, Heart failure, and Lung cancer also contribute significantly to mortality.

Category:Interstitial lung diseases Category:Idiopathic diseases Category:Pulmonology