Pulmonary Fibrosis

 

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Definition

Pulmonary Fibrosis (PF) describes a condition in which the lung tissue becomes thickened, stiff, and scarred. The medical terminology used to describe this scar tissue is fibrosis. The alveoli and the blood vessels within the lungs are responsible for delivering oxygen to the body, including the brain, heart, and other organs. As lung tissue becomes scarred and thicker, it is more difficult for the lungs to transfer oxygen into the bloodstream. As a result, the brain, heart, and other organs do not get the oxygen they need to function properly. In some cases, doctors can determine the cause of the fibrosis, but in many cases the cause remains unknown. When there is no known cause for the development of pulmonary fibrosis (and certain radiographic and/or pathologic criteria are met), the disease is called idiopathic pulmonary fibrosis or IPF. More specifically, consensus treatment guidelines from international lung societies define IPF as “a specific form of chronic, progressive fibrosing interstitial pneumonia of unknown cause, occurring primarily in older adults, limited to the lungs, and associated with the histopathologic and/or radiologic pattern of UIP [usual interstitial pneumonia].

If there is a clear association with another illness or the lung fibrosis is the result of a side effect from a medication or an exposure to an agent known to cause PF, then the cause of the disease is no longer considered idiopathic. PF clearly associated with another disease, such as scleroderma or rheumatoid arthritis, would be referred to as pulmonary fibrosis secondary to scleroderma or secondary to rheumatoid arthritis.

Idiopathic pulmonary fibrosis portends a poor prognosis, with an estimated mean survival of 2-5 years from the time of diagnosis.Estimated mortality rates are 64.3 deaths per million in men and 58.4 deaths per million in women.

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Incidence and Prevalence

There are no reliable data to determine how many people are affected by PF, possibly due to the large number of conditions under which it can arise.

According to the ATS, the incidence of IPF was estimated at 10.7 cases per 100,000 per year for men and 7.4 cases per 100,000 per year for women in a population-based study from the county of Bernalillo, New Mexico. A study from the United Kingdom reported an overall incidence rate of only 4.6 per 100,000 person-years, but estimated that the incidence of IPF increased by 11% annually between 1991 and 2003. This increase was not felt to be attributable to the aging of the population or increased ascertainment of milder cases. A third study from the United States estimated the incidence of IPF to be between 6.8 and 16.3 per 100,000 persons using a large database of healthcare claims in a health plan.

Prevalence estimates for IPF have varied from 2 to 29 casesper 100,000 in the general population. The wide rangein these numbers is likely explained by the previous lack of uniform definition used in identifying cases of IPF, as well as by differences in study designs and populations. A recent analysis based on healthcare claims data of a large health plan in the United States yielded a prevalence estimate of between 14.0 and 42.7 per 100,000 persons depending on the case definition used. It is unknown if the incidence and prevalence of IPF are
influenced by geographic, ethnic, cultural, or racial factors.

Causes

• Idiopathic Disorders: Idiopathic Pulmonary Fibrosis(IPF), acute interstitial pneumonia(AIP), idiopathic non-specific interstitial pneumonia(NSIP), sarcoidosis.
• Connective tissue and Autoimmune disease: Sleroderma/Progressive systemic sclerosis, Lupus, Rheumatoid arthritis(RA), polyomyositis/dermatomyositis.
• Occupational and Environmental: Inorganic dust, organic dust, gases and fumes, radiation.
• Drug Induced: Chemotherapeutic agent, radiation therapy, antiarrythmics, antibiotics, anticonvulsants.
• Infections: Viral and bacterial.
• Genetic/Inherited: Familial pulmonary fibrosis, Hermansky-Pudlak syndrome.

Other factors associated with the disease is heavy smoking and acid reflux disease(GERD).

Diagnostic Procedures

• Laboratory studies: Reportedly, up to 30% of patients with idiopathic pulmonary fibrosis (IPF) have positive tests for antinuclear antibodies or rheumatoid factor; however, these titers are generally not high.
• Chest Radiography: The typical findings are peripheral reticular opacities (netlike linear and curvilinear densities) predominantly at the lung bases (see image below). Honeycombing (coarse reticular pattern) and lower lobe volume loss can also be seen.
• High resolution Computing tomography.
• 6 minute walk test:  Desaturation below the threshold of 88% during the 6MWT has been associated with an increased mortality.
• Pulmonary function testing: In patients with idiopathic pulmonary fibrosis, a restrictive ventilatory defect is typically present. Vital capacity, functional residual capacity, total lung capacity, and forced vital capacity (FVC) all are reduced. Additionally, the static pressure-volume curve is shifted downward and to the right as a result of decreased lung compliance. Obstructive ventilatory defects are not common; however, if present, they may suggest the coexistence of chronic obstructive pulmonary disease.
• Bronchoalveolar lavage.
• Transthoracic echocardiography.
• Surgical lung biopsy.

In order to diagnose Idiopathic Pulmonary Fibrosis, which is the most common type, the following diagnostic criteria have to be present:

• The exclusion of other known causes of interstitial lung disease (ILD), including domestic and occupational environmental exposures, connective tissue disease, and drug toxicity.
• The presence of a UIP pattern on HRCT in patients not subjected to a surgical lung biopsy.
• Specific combinations of HRCT and surgical lung biopsy pattern in patients subjected to surgical lung biopsy.

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Treatment

Treatment courses for pulmonary fibrosis are highly variable and difficult to predict. Each therapy strategy is individualized according to the patient's history and symptoms. 

Thepharmacologic treatment options include Cyclophosphamide, Azathioprine, N-acetylcysteine, Pirfenidone. They medications may stabilize their disease and there may be a benefit to continuing usage. Further, some of these medications may be prescribed to manage symptoms when a patient has an acute exacerbation or period of worsening. Medications may be used alone or in combination. Also,  as fibrosis inhibits an adequate transfer of oxygen into the bloodstream, some patients may require supplemental oxygen. This helps to reduce breathlessness, enabling the patient to be more active. Some patients may need oxygen therapy all the time while others may only need it during sleep and exercise. 

The non-pharmacologic treatment option is pulmonary rehabilitation. Pulmonary rehabilitation programs involve aerobic conditioning, strength and flexibility training, educational lectures, nutritional interventions, and psychosocial support. Pulmonary rehabilitation has recently been studied in patients with ILD. Two controlled trials of pulmonary rehabilitation in IPF have demonstrated an improvement in walk distance and symptoms or quality of life. Other uncontrolled studies have found similar findings. The beneficial effects of pulmonary rehabilitation may be more pronounced in patients with worse baseline functional status. Pulmonary rehabilitation may not be reasonable in a minority.

Lung trasplantation for Idiopathic Pulmonary Fibrosis patients confer a survival benefit over medical therapy. Due to the use of the Lung Allocation Score(LAS) IPF has now replaces COPD as the most common indication for lung transplantation in the United States.

Physiotherapy in Pulmonary Fibrosis

add text here relating to the differential diagnosis of this condition

References

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