Pulmonary fibrosis (literally "scarring of the lungs") is a respiratory disease in which scars are formed in the lung tissues, leading to serious breathing problems. Scar formation, the accumulation of excess fibrous connective tissue (the process called fibrosis), leads to thickening of the walls, and causes reduced oxygen supply in the blood. As a consequence patients suffer from perpetual shortness of breath.
In some patients the specific cause of the disease can be diagnosed, but in others the probable cause cannot be determined, a condition called idiopathic pulmonary fibrosis. There is no known cure for the scars and damage in the lung due to pulmonary fibrosis.
Symptoms of pulmonary fibrosis are mainly:
- Shortness of breath, particularly with exertion.
- Chronic dry, hacking coughing.
- Fatigue and weakness.
- Chest discomfort including chest pain.
- Loss of appetite and rapid weight loss.
Pulmonary fibrosis is suggested by a history of progressive shortness of breath (dyspnea) with exertion. Sometimes fine inspiratory crackles can be heard at the lung bases on auscultation, (the use of a stethoscope). A chest x-ray may or may not be abnormal, but high-resolution CT will frequently demonstrate abnormalities.
Pulmonary fibrosis may be a secondary effect of other diseases. Most of these are classified as interstitial lung diseases. Examples include autoimmune disorders, viral infections and bacterial infection like tuberculosis which may cause fibrotic changes in both lungs upper or lower lobes and other microscopic injuries to the lung. However, pulmonary fibrosis can also appear without any known cause. In this case, it is termed "idiopathic". Most idiopathic cases are diagnosed as idiopathic pulmonary fibrosis. This is a diagnosis of exclusion of a characteristic set of histologic/pathologic features known as usual interstitial pneumonia (UIP). In either case, there is a growing body of evidence which points to a genetic predisposition in a subset of patients. For example, a mutation in surfactant protein C (SP-C) has been found to exist in some families with a history of pulmonary fibrosis.
Diseases and conditions that may cause pulmonary fibrosis as a secondary effect include:
- Inhalation of environmental and occupational pollutants, such as metals in asbestos, silicosis and exposure to certain gases. Coal miners, ship workers and sand blasters among others are at higher risk.
- Hypersensitivity pneumonitis, most often resulting from inhaling dust contaminated with bacterial, fungal, or animal products.
- Cigarette smoking can increase the risk or make the illness worse.
- Some typical connective tissue diseases such as rheumatoid arthritis, SLE and scleroderma.
- Other diseases that involve connective tissue, such as sarcoidosis and granulomatosis with polyangiitis.
- Certain medications, e.g. amiodarone, bleomycin (pingyangmycin), busulfan, methotrexate, apomorphine, and nitrofurantoin.
- Radiation therapy to the chest.
Pulmonary fibrosis involves gradual exchange of normal lung parenchyma with fibrotic tissue. The replacement of normal lung with scar tissue causes irreversible decrease in oxygen diffusion capacity, and the resulting stiffness or decreased compliance makes pulmonary fibrosis a restrictive lung disease. Pulmonary fibrosis is perpetuated by aberrant wound healing, rather than chronic inflammation. It is the main cause of restrictive lung disease that is intrinsic to the lung parenchyma. In contrast, quadriplegia and kyphosis are examples of causes of restrictive lung disease that do not necessarily involve pulmonary fibrosis.
The diagnosis can be confirmed by lung biopsy. A videoscopic assisted thoracoscopic wedge biopsy (VATS) under general anesthesia may be necessary to obtain enough tissue to make an accurate diagnosis. This kind of biopsy involves placement of several tubes through the chest wall, one of which is used to cut off a piece of lung to send for evaluation. The removed tissue is examined histopathologically by microscopy to confirm the presence and pattern of fibrosis as well as presence of other features that may indicate a specific cause e.g. specific types of mineral dust or possible response to therapy e.g. a pattern of so-called non-specific interstitial fibrosis.
Misdiagnosis is common because, while overall pulmonary fibrosis is not rare, each individual type of pulmonary fibrosis is uncommon and the evaluation of patients with these diseases is complex and requires a multidisciplinary approach. Terminology has been standardized but difficulties still exist in their application. Even experts may disagree with the classification of some cases. On spirometry, as a restrictive lung disease, both the FEV1 (forced expiratory volume in 1 second) and FVC (forced vital capacity) are reduced so the FEV1/FVC ratio is normal or even increased in contrast to obstructive lung disease where this ratio is reduced. The values for residual volume and total lung capacity are generally decreased in restrictive lung disease.
Asbestosis, Mesothelioma, Pulmonary Fibrosis and Idiopathic Pulmonary Fibrosis: Asbestosis is also known as Mesothelioma or Pulmonary Fibrosis. These diseases and their similarities are often subject to many clinical trials and studies to differentiate them from each other with some medical professionals disagreeing on their differences. Asbestosis generally progresses slowly, whereas malignant mesothelioma has an extremely poor prognosis. The treatment of patients with asbestos exposure and lung cancer is identical to that of any patient with lung cancer. Because exposure to cigarette smoke increases the risk of developing lung cancer in patients with a history of asbestos exposure, smoking cessation is essential. In many respects, asbestosis is clinically similar to idiopathic pulmonary fibrosis, but asbestosis usually progresses slowly, whereas idiopathic pulmonary fibrosis has a rapidly progressive course. No current treatment effectively alters the natural course of asbestosis.
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