Pulmonary Fibrosis (Lung Fibrosis)

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In pulmonary fibrosis, excess fibrous connective tissue develops in the lungs. It presents initially with dyspnea, loss of appetite, fatigue and dry cough.


Presentation

The most pronounced clinical feature of pulmonary fibrosis is progressive exertional dyspnea associated with the production of dry cough.

On examination, there is gross clubbing of the fingernails and toenails. The movements of chest on the affected side are reduced. The trachea is shifted if there is fibrosis of the upper lobe. In fibrosis o the lower lobe, there is shifting of the heart and hence the apex beat. Percussion not is also dull over the affected area. Numerous end-inspiratory crepitations are also audible on auscultation.

In severe disease, there may be cyanosis eventually leading to respiratory failure, pulmonary hypertension and cor pulmonale.

Workup

The diagnosis of pulmonary fibrosis is assisted by the use of the following investigations.

  • Chest radiography: Radiography of the chest will show diffuse pulmonary opacities most obvious in the lower zones. The hemidiaphragms are also high due to the pulling effect of fibrosis and the lungs appear small. In advanced cases, the lungs have a honeycomb appearance with diffuse pulmonary shadowing interspersed with small cystic translucencies.
  • High resolution Computerized Tomogaphy (CT): Computerized Tomography is much more helpful than radiographs in the early stages of the disease. It has enhanced the diagnostic accuracy as it can detect lesions that are absent or only slight on chest x-rays [7].
  • Pulmonary function tests: Pulmonary function tests indicate the presence of a restrictive lung disease. There is a proportionate reduction in forced expiratory volume and vital capacity.
  • Arterial blood gases: In pulmonary fibrosis, evaluation of the arterial blood gases demonstrates hypoxemia with normal partial pressure of carbon dioxide.
  • Bronchoalveolar lavage: This shows an increased cellularity in the lavage fluid. Neutrophils, in particular, are significantly high [8].
  • Lung biopsy: Transbronchial lung biopsy is of no use in diagnosing pulmonary fibrosis; however, open lung biopsy may be helpful.

Treatment

In acute conditions, oxygen is given to the patient to reduce hypoxemia and to reverse cyanosis [9].

Treatment with corticosteroids is beneficial in around 30% of the patients. A trial of prednisolone with 40 to 60 mg per day is started in the patients in the patients with progressive disease. The response to treatment is evaluated over a period of 6 to 8 weeks. If the response is good, the dose is reduced to 5 or 10 mg per day. If there is no response, the dosage is tapered and stopped.

Azathioprine or cyclophosphamide may be added if there is no response to prednisolone therapy. They are also used if there is a relapse on reducing the dose of prednisolone [10].

In severe disease, lung transplantation should be considered as the definitive cure.

Prognosis

Once fibrosis has developed, it is not reversible. The prognosis is good if the disease is detected early and its progression stopped through adequate treatment. If fibrosis is extensive, lung transplantation may be the only option.

Etiology

Pulmonary fibrosis can occur due to a number of well-established causes that are listed below [1].

  • Exposure to inorganic dusts causes fibrosing lung diseases that are referred to as pneumoconiosis. These include silicosis, anthracosis, asbestosis and berylliosis and are caused by silica dust, coal dust, asbestosis and beryllium respectively [2].
  • The use of certain drugs such as methotrexate, amiodarone, bleomycin, busuphan and hydralazine is also associated with the development of pulmonary fibrosis [3] [4].
  • Aspiration of gastric fluid into the lungs can also lead to the development of pulmonary fibrosis.
  • Overdose of radiation to the chest can also cause pulmonary fibrosis [5].

Other less important causes of pulmonary fibrosis include the following.

Epidemiology

The epidemiology of pulmonary fibrosis is not very well documented. It is estimated that up to 5 million people are affected worldwide. The incidence of idiopathic pulmonary fibrosis is higher in people over the age of 50 years.

Sex distribution
Age distribution

Pathophysiology

The initial insult in the development of pulmonary fibrosis is injury to the epithelial surface. This leads to the development of inflammation in the air spaces and the walls of the alveoli, leading to an acute phase of alveolitis. The disease then spreads to the adjacent portions of the interstitium and vasculature, ultimately leading to fibrosis.

It has been suggested that fibrosis is caused by the release of fibronectin and growth factors from alveolar macrophages following tissue injury caused by the release of oxidants from neutrophils, eosinophils and macrophages [6].

Histologically, pulmonary fibrosis is characterized by cellular infiltration along with thickening and fibrosis of the walls of the alveoli. The degree of fibrosis is variable and is often progressive.

Prevention

Idiopathic pulmonary fibrosis can not be prevented. However, pulmonary fibrosis of known etiology can be prevented by avoiding exposure to silica dust, asbestos, coal dust and beryllium. The people who come in contact with these dusts in their occupation should use proper masks.
The overuse of methotrexate, amiodarone, hydralazine, bleomycin and busuphan should be avoided.

Summary

Pulmonary fibrosis is not a single disease entity. It is a part of a group of disorders that are known as interstitial lung diseases. The common features in these disease include:

  • Thickening of the alveolar walls by fibrosis and edema
  • Increased stiffness of the lungs associated with exertional dyspnea
  • Maldistribution of pulmonary ventilation and perfusion leading to hypoxemia

Patient Information

Pulmonary fibrosis refers to the thickening and hardening of the walls of the alveoli of the lungs. This condition causes a reduction in the amount of expansion and capacity of the lungs. As a result, the function of the lungs is rendered short and the patient becomes breathless upon any kind of exertion. The disease is progressive if not treated properly. Lung transplantation may be the only treatment option in advanced cases.

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References

  1. Kronenberger H. [Etiology of pulmonary fibrosis]. Pneumologie. Jun 1991;45(6):439-446.
  2. Kolev K, Burkova T. [Histochemical mechanisms in etiology of pulmonary fibrosis after short-term exposure to a mixture of dust and quartz from copper mine]. Problemi na khigienata. 1982;7:88-97.
  3. Fuzesi K, Karolyi A. [Amiodarone-induced pulmonary fibrosis]. Orvosi hetilap. Jan 5 1997;138(1):43.
  4. Hesterberg TW, Gerriets JE, Reiser KM, Jackson AC, Cross CE, Last JA. Bleomycin-induced pulmonary fibrosis: correlation of biochemical, physiological, and histological changes. Toxicology and applied pharmacology. Sep 15 1981;60(2):360-367.
  5. Isobe K, Hata Y, Sakamoto S, Takai Y, Shibuya K, Homma S. Clinical characteristics of acute respiratory deterioration in pulmonary fibrosis associated with lung cancer following anti-cancer therapy. Respirology. Jan 2010;15(1):88-92.
  6. Crestani B. [Pathophysiology of idiopathic pulmonary fibrosis]. Bulletin de l'Academie nationale de medecine. Feb 2010;194(2):343-351; discussion 351-342.
  7. Oda K, Ishimoto H, Yatera K, et al. High-resolution CT scoring system-based grading scale predicts the clinical outcomes in patients with idiopathic pulmonary fibrosis. Respiratory research. 2014;15:10.
  8. Watters LC, Schwarz MI, Cherniack RM, et al. Idiopathic pulmonary fibrosis. Pretreatment bronchoalveolar lavage cellular constituents and their relationships with lung histopathology and clinical response to therapy. The American review of respiratory disease. Mar 1987;135(3):696-704.
  9. Honma Y, Ogasawara H. [Pathophysiology and treatment of acute exacerbation of pulmonary fibrosis]. Kokyu to junkan. Respiration & circulation. Apr 1986;34(4):377-383.
  10. Kondoh Y, Taniguchi H, Yokoi T, et al. Cyclophosphamide and low-dose prednisolone in idiopathic pulmonary fibrosis and fibrosing nonspecific interstitial pneumonia. The European respiratory journal. Mar 2005;25(3):528-533.

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