Pulmonary Fibrosis

Pathophysiology

Despite the etiology or variance in the course of disease among patients, the process leading to lung fibrosis remains constant. Mechanical, chemical, or physical injury to lung tissue all have potential to initiate an inflammatory process that inflicts damage to virtually all components of lungs including the airways, air sacs, and vasculature.

Inflammation may either progress and become chronic leading to permanent scarring (i.e., pulmonary fibrosis) or resolve, resulting in healing. In cases of the former, subsequent fibrosis results in permanent loss of normal lung function and manifests through severe respiratory symptoms. Such symptoms are a result of physiologic consequences attributed to the lungs inability to carry sufficient amounts of oxygen and deterred ability to exchange vital gasses. However, the severity of the disease is dependent on the extent of inflammatory damage.

Clinical Manifestations

The condition is demanding of a thorough history inclusive of environmental factors, hobbies, drug use, and autoimmune conditions. Symptoms of exertion-al dyspnea (shortness of breath), chest pain, cough, fatigue, fever, and diminished exercise tolerance are most common. Physical examination may be unremarkable with the exception of auscultated inspiratory crackles. However, in advanced conditions, symptoms of heart failure accompanied with lower extremity swelling are often noted.

Diagnostic tests include blood tests, pulmonary function tests, imaging studies, and if necessary, a lung biopsy. Although laboratory studies seldom provide [Page 1456]diagnostic aid leading to a diagnosis, they often help to exclude secondary causes of fibrosis. Inflammatory markers such as elevated erythrocyte sedimentation rate (ESR) and immune complexes are commonly documented findings among disease carriers. Other autoimmune markers such as rheumatoid factor (RF) and antinuclear antibodies (ANA) are often unusually positive in patients even in the absence of an organic autoimmune condition.

Pulmonary function studies are most distinguishing indicating an abnormal restrictive pattern and arterial blood gas studies often disclose hypoxia (decreased blood oxygen level).

Diagnostically, chest X-ray (CXR) and high-reso-lution computerized axial tomography (HRCT) scan frequently demonstrate a trademark “honeycombing” lesion specific to fibrosis. However, HRCT is the preferred imaging study as CXR has been reported to exhibit normal results in as many as 10 percent of patients. In the event that imaging studies show no changes, a video-assisted thoracoscopic (VAST) lung biopsy is indicated to make the diagnosis for pulmonary fibrosis. During this procedure, a sample of the cellular tissue is extracted and analyzed by a pathologist to make the diagnosis. However, a lung biopsy is not routinely necessary when imaging studies are strongly remarkable for the aforementioned fibrotic changes.

Treatment and Prognosis

As yet, no cure for pulmonary fibrosis exists. However, current treatment guidelines are designed to deter the progression of disease and reduce symptoms. Unfortunately, prognosis is typically poor among the majority of patients. Patients with better prognosis include disease carriers of younger age, female gender, milder respiratory symptoms, and good response to treatment. Treatment approaches entail the administration of corticosteroid therapy to reduce the production of inflammatory mediators and immunosuppressive medications such as cyclophosphomide or azathioprine to prevent disease succession.

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