Pleural fibrosis is a condition characterized by the thickening and hardening of the pleura, the thin, two-layered membrane surrounding the lungs and lining the chest cavity. This scarring process causes the normally flexible pleura to become stiff and rigid, compressing the underlying lung tissue. When the lung is restricted by this hardened shell, its ability to expand fully during inhalation is compromised, leading to impaired respiratory function. The severity ranges from small, localized areas of scarring to widespread, dense thickening.
Understanding the Pleural Membranes and Scarring
The pleura consists of two layers: the visceral pleura, which closely covers the lung surface, and the parietal pleura, which lines the inside of the chest wall. Between these two layers is the pleural space, containing a small amount of fluid that allows the layers to glide smoothly against each other during respiration. Injury or chronic inflammation in this space disrupts the delicate balance of healing, leading to an excessive deposition of matrix components like collagen. This overgrowth of fibrous tissue, or scarring, is what defines pleural fibrosis.
The pathological process involves the activation of mesothelial cells and subpleural fibroblasts, which begin to produce scar tissue instead of allowing for normal repair. This mechanism involves a disordered turnover of fibrin within the pleural space. A distinction exists between pleural plaques, which are localized, often calcified areas of fibrosis usually on the parietal pleura, and diffuse pleural thickening. Diffuse thickening is more widespread, often involves the visceral pleura, and is the form more likely to significantly restrict lung expansion and cause symptoms. Clinically significant fibrosis requires involvement of the visceral pleura.
Primary Causes of Pleural Fibrosis
The development of pleural fibrosis follows severe inflammation within the pleural space, often associated with a fluid accumulation known as an exudative pleural effusion. The most widely recognized cause is long-term occupational exposure to asbestos fibers, which can migrate to the pleura and trigger chronic inflammation. Asbestos-related pleural disease can manifest as pleural plaques or the more extensive diffuse pleural thickening.
Infections that affect the chest cavity are another major cause, particularly bacterial pneumonia leading to empyema (the collection of pus in the pleural space), and tuberculosis. These infections trigger intense inflammatory responses that leave behind a thick, fibrous rind. Trauma to the chest, such as a rib fracture or a penetrating injury resulting in a hemothorax (a collection of blood in the pleural space), can also initiate the scarring process. Bleeding within the pleural cavity leads to the formation of a fibrin matrix that eventually organizes into dense fibrotic tissue.
Certain autoimmune and inflammatory conditions, including rheumatoid arthritis and systemic lupus erythematosus, can cause pleurisy (inflammation of the pleura), which sometimes progresses to fibrosis. Drug-induced reactions and radiation therapy to the chest have also been implicated as less common causes of pleural scarring. The resulting fibrosis can encase the lung, a condition sometimes termed fibrothorax, which severely limits the ability of the lung to inflate.
Identifying Symptoms and Diagnostic Imaging
The clinical presentation depends on the extent and location of the scarring, but the most common symptom is progressive shortness of breath, or dyspnea, particularly during physical exertion. The restriction of lung movement means the patient cannot take a deep breath, leading to reduced exercise tolerance and a feeling of chronic tightness in the chest. Some individuals may also experience persistent chest pain due to the inflammation or the pulling sensation from the thickened pleura.
Diagnosis begins with imaging studies, where a standard Chest X-ray may show areas of pleural thickening or calcification. However, a high-resolution Computed Tomography (CT) scan is the preferred method, as it provides definitive, detailed images of the pleura and underlying lung tissue. The CT scan accurately measures the extent of the thickening and can differentiate between benign plaques and the more restrictive diffuse fibrosis.
Pulmonary function tests (PFTs) are often used to measure the functional impact of the fibrosis on breathing mechanics. These tests typically reveal a restrictive ventilatory defect, meaning the total volume of air the lungs can hold is reduced. Specifically, the tests show a decreased total lung capacity and a reduced forced vital capacity, confirming that the stiffened pleura is physically preventing the lung from expanding properly.
Treatment and Long-Term Management
Once the dense, collagen-rich scar tissue of pleural fibrosis has fully formed, the process is generally irreversible, meaning no medication can dissolve the established scarring. Treatment is primarily focused on managing symptoms, addressing the underlying cause if possible, and maintaining the patient’s quality of life. For cases caused by ongoing infection, such as empyema, immediate treatment with antibiotics and drainage is necessary to prevent further fibrosis.
Symptom management includes pain control for chronic chest discomfort and supplemental oxygen therapy for patients with low blood oxygen levels. Pulmonary rehabilitation is a cornerstone of long-term care, offering tailored exercise training, breathing techniques, and education to help patients maximize their remaining lung function and physical endurance. This supportive approach helps individuals cope with the limitations imposed by the condition.
In severe cases where the thickened pleura forms a dense, unyielding peel that severely restricts lung function, a surgical procedure called decortication may be considered. Decortication involves carefully stripping the fibrous, rind-like layer from the lung surface to allow the trapped lung to re-expand. This surgery is typically reserved for symptomatic patients with chronic, extensive fibrosis who are otherwise good surgical candidates.