Pulmonary Fibrosis Causes, Symptoms, Diagnosis, Treatment, Prevention

Pulmonary Fibrosis Causes, Symptoms, Diagnosis, Treatment, Prevention


What is pulmonary fibrosis?


"Fibrosis" is a term used to refer to scarring, so pulmonary fibrosis means scarring throughout the lungs. Pulmonary fibrosis can be caused by many conditions including chronic inflammatory processes (sarcoidosis, Wegener's granulomatosis ), infections, environmental agents (asbestos, silica, exposure to certain gases), exposure to ionizing radiation (such as radiation therapy to treat tumors of the chest), chronic conditions (lupus, rheumatoid arthritis), and certain medications.

In a condition known as hypersensitivity pneumonitis, fibrosis of the lung can develop following a heightened immune reaction to inhaled organic dusts or occupational chemicals. This condition most often results from inhaling dust contaminated with bacterial, fungal, or animal products.

In some people, chronic pulmonary inflammation and fibrosis develop without an identifiable cause. Most of these people have a condition called idiopathic pulmonary fibrosis (IPF) that does not respond to medical therapy, while some of the other types of fibrosis, such as nonspecific interstitial pneumonitis (NSIP), may respond to immune suppressive therapy.

Synonyms (other names) for various types of pulmonary fibrosis that have been used in the past include chronic interstitial pneumonitis, Hamman-Rich syndrome, and diffuse fibrosing alveolitis.

Causes of Pulmonary Fibrosis


There are many potential causes of pulmonary fibrosis, such as:

  • rheumatoid arthritis
  • scleroderma
  • lupus
  • mineral dusts - coal, silicon, asbestos (asbestosis), metals
  • poisonous industrial gases such as chlorine and sulphur dioxide
  • radiation treatment to the chest
  • poisons - particularly paraquat
  • medications (e.g., nitrofurantoin, amiodarone, bleomycin, cyclophosphamide methotrexate)
The cause of pulmonary fibrosis, especially when it is idiopathic, is poorly understood. It probably involves deregulation of the immune system in the lungs, but some experts still think it might be caused by an unknown environmental exposure, or even an unusual infection.

A few families are particularly affected by idiopathic pulmonary fibrosis, which may be categorized into two forms - an environmental form and a rarer genetic form. Pulmonary fibrosis is more likely caused by environmental factors in genetically susceptible people. These people have immune systems that overreact in the presence of particular irritants or organisms. This would be typical of autoimmune disease.

The mechanism of the disease is as follows: The lungs become inflamed, usually for no clear reason. White blood cells and liquid fill the alveoli (the lung's tiny air pockets where oxygen is transferred to the blood). If the liquid remains for long enough, blood-clotting agents solidify, leaving scars that can interfere with the function of the alveoli.

The blood vessels of the lungs are separated from the air pockets by walls called interstitia. The interstitium allows oxygen to reach the blood, and carbon dioxide from the blood to pass into the lungs to be breathed out. Fibrosis damages this membrane, thickening it and thus reducing the lungs' ability to add oxygen and remove carbon dioxide from the blood.

Triggers


A number of factors have been suggested as possible triggers for the initial damage to the cells lining the alveoli, including:
  • Cigarette smoking – the disease is more common in current smokers or those who have smoked in the past.
  • Viral infections such as the Epstein-Barr virus or hepatitis C
  • Breathing in wood dust and/or metal dust – people in occupations where this can occur, such as carpentry, have a slightly higher risk o developing IPF
  • Gastro-oesophageal reflux disease (GORD), a condition where the acid from your stomach rises back up into your throat – this may be accidentally inhaled into the lungs, causing damage to the alveoli
  • Genetic tendency – the condition appears to run in some families
As IPF is such a rare condition it is hard to estimate how much of an impact these risk factors can have on your chance of developing IPF.

Most experts agree that the two most significant risk factors are:
  • being a smoker or having smoked in the past
  • exposure to wood and metal dust

Symptoms and Complications of Pulmonary Fibrosis


For the majority of people, the symptoms of pulmonary fibrosis come on slowly over the course of months to years, but for some people the symptoms can develop more rapidly.

Most people with pulmonary fibrosis first see their doctor about increasing shortness of breath during exercise. Some also have a cough. These are often the only symptoms of early pulmonary fibrosis, but you might also feel one or more of the following symptoms:

  • loss of stamina
  • loss of appetite
  • fatigue
  • weight loss
  • diffuse chest pain
Later on, symptoms can include:

  • shortness of breath without exercise - eating, talking, or just resting
  • cyanosis (blue lips, nail beds, and sometimes skin due to lack of oxygen in the tissue)
  • clubbing of the fingers (enlarged fingertips)
Pulmonary fibrosis can lead to several severe complications. Because the lungs don't take in oxygen as well, low blood oxygen levels (hypoxemia) can develop. Lack of oxygen can affect the entire body.

Another complication of pulmonary fibrosis is pulmonary hypertension (high blood pressure in the arteries of the lungs). Scar tissue in the lungs can make it more difficult for blood to flow through them. The increased pressure makes the heart work harder and leads to a weakened and enlarged heart, reducing its pumping efficiency and producing heart failure. This is suspected when people develop fluid accumulations in the abdomen, leg swelling, or prominent pulsations in neck veins.

How is pulmonary fibrosis diagnosed?


Pulmonary fibrosis is suggested by a history of progressive (worsening over time) shortness of breath with exertion. Sometimes, during examination of the lungs with a stethoscope, the doctor can hear crackling sounds in the chest. These crackles have a very characteristic sound and are very similar to the sound heard when Velcro is pulled apart. These are often referred to as "Velcro crackles (or rales)". The chest X-ray may or may not be abnormal, but a special X-ray test called a high resolution CT scan will frequently demonstrate abnormalities. This type of X-ray provides a cross sectional picture of the lungs in very detailed resolution. The classic findings in idiopathic pulmonary fibrosis show diffuse peripheral scarring of the lungs with small bubbles (known as bullae) adjacent to the outer lining of the surface of the lung, often at the bases of the lungs.

Lung function testing is distinctly abnormal. The volumes of the lungs may be reduced as may the airflow, but the characteristic finding is a reduction in the diffusing capacity. The diffusing capacity is a measure of the ability of the lungs to exchange gases (oxygen and carbon dioxide) into and out of the blood stream.

The diagnosis can be confirmed by lung biopsy. An open surgical biopsy, meaning that the chest wall must be surgically opened under general anesthesia to remove a portion of lung tissue, may be necessary to obtain enough tissue to make an accurate diagnosis. The most common type of biopsy in this situation is by a video assisted thoracoscope. Basically, this involves placing a small tube into the chest cavity through which biopsy samples can be obtained. Often, if the clinical situation is very classical in presentation, a biopsy may be unnecessary. The biopsy specimen is examined microscopically by a pathologist to confirm the presence of fibrosis.

How is the pulmonary fibrosis treated?


The treatment options for idiopathic pulmonary fibrosis are very limited. There is no evidence that any medications can help this condition, since scarring is permanent once it has developed. Lung transplantation is the only therapeutic option available. At times, this diagnosis can be difficult to make even with tissue biopsy reviewed by pathologists with specific experience in this field. Research trials using different drugs that may reduce fibrous scarring are ongoing.

Since some types of lung fibrosis can respond to corticosteroids (such as prednisone) and/or other medications that suppress the body's immune system, these types of drugs are sometimes prescribed in an attempt to decrease the processes that lead to fibrosis. These drugs do not help idiopathic pulmonary fibrosis but in some cases, other causes of lung fibrosis responsive to immune suppression may mimic the appearance of idiopathic pulmonary fibrosis.

The immune system is felt to play a central role in the development of many forms of pulmonary fibrosis. The goal of treatment with immune suppressive agents such as corticosteroids is to decrease lung inflammation and subsequent scarring. Responses to treatment are variable. Once scarring has developed, it is permanent. Those whose conditions improve with immune suppressive treatment probably do not have idiopathic pulmonary fibrosis.

The toxicity and side effects of treatments can be serious. Therefore, patients with pulmonary fibrosis should be followed by a lung specialist experienced in this condition. The lung specialist will determine the need for treatment, the duration of treatment, and will monitor the response to therapy along with any side effects.

Only a minority of patients respond to corticosteroids alone, so other immune-suppressing medications are used in addition to corticosteroids. These include

  • cyclophosphamide (Cytoxan),
  • azathioprine (Imuran, Azasan),
  • methotrexate (Rheumatrex, Trexall),
  • penicillamine (Cuprimine, Depen), and
  • cyclosporine.
The anti-inflammatory medication colchicine has also been used with limited success. Other trials using newer drugs such as gamma interferon, mycophenolate mofetil (Cellcept), and pirfenidone have not met with much success in the treatment of idiopathic pulmonary fibrosis.

Pulmonary fibrosis causes decreased oxygen levels in the blood. A decrease in blood oxygen level (hypoxia) can lead to elevated pressure in the pulmonary artery (the vessel that carries blood from the heart to the lungs to receive oxygen), a condition known as pulmonary hypertension, which can in turn lead to failure of the right ventricle of the heart. Therefore, patients with pulmonary fibrosis are frequently treated with supplemental oxygen to prevent pulmonary hypertension. In some cases, new agents used to lower the blood pressure in the pulmonary artery have had limited benefit.

There is also evidence that patients suffering from pulmonary fibrosis may be at increased risk for blood clots that travel to the lung (pulmonary emboli), and therefore anticoagulation (blood thinning) therapy may be indicated.

Can pulmonary fibrosis be prevented?


Idiopathic pulmonary fibrosis has shown an increased frequency is cigarette smokers. This is just one more reason not to smoke or quit if you do. The cause of idiopathic pulmonary fibrosis is unknown, and therefore prevention is difficult. There is a rare form of idiopathic pulmonary fibrosis that runs in families.

Exercise can improve the body's ability to provide oxygen to the tissues, and maximize the efficiency of healthy lung tissue. People with advanced pulmonary fibrosis may need oxygen equipment in order to maintain an adequate supply of oxygen in their circulation.

It's difficult to prevent a disease when you don't know what causes it, so there's no generally accepted preventive advice for pulmonary fibrosis. However, people who have jobs that increase their risk of developing pulmonary fibrosis (e.g., farmers who work with hay, miners, welders, sandblasters, demolition workers) should do what they can to minimize exposure (e.g., wearing masks).

There is no evidence that special diets or supplements or bowel preparations will help this disease in any way.