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Fibrothorax on chest x-ray
Dense fibrous tissue may form over the pleural surface for a variety of reasons. Pleural fibrosis usually follows intense inflammation of the pleura; however, the mechanisms following the inflammatory process leading up to fibrosis are unclear. Profibrotic cytokines, especially transforming growth factor-β (TGF-β), probably play a significant role. In various animal models, TGF-β, administered directly or via vector transfection, induces pleural fibrosis, and anti–TGF-β antibodies can inhibit pleural adhesion formation in empyema.
A fibrothorax most commonly develops as a complication of an empyema or a hemothorax. Fibrothorax has also developed as a complication of tuberculosis, collagen vascular diseases, uremia, paragonimiasis, and drug reactions. Pleural fibrosis can be idiopathic, and isolated familial cases have been reported. Whereas tuberculous pleuritis is common, fibrothorax is a rare complication. In one study, restrictive functional sequelae were found in 10% of 81 patients with tuberculous pleuritis, but were mostly mild. Neither the early drainage of the pleural effusion nor the use of systemic corticosteroids has significant impact on subsequent development of pleural thickening or restrictive lung function in patients with tuberculous pleuritis. Pleural fluid inflammatory markers are, at best, weak predictors of eventual pleural thickening.
Asbestos exposure may also lead to a fibrothorax (also called diffuse pleural thickening), which is usually bilateral. In these cases, extensive fibrosis of the visceral pleura develops, together with areas of adhesion with the parietal surfaces, thus obliterating the pleural space. Diffuse pleural thickening is known to follow benign asbestos pleural effusions, and it has been suggested that this is a necessary precursor of fibrothorax. In one series of 44 patients with diffuse pleural thickening, half had a history of benign asbestos effusion; conversely, 54% of those who had a benign asbestos effusion had residual pleural thickening. Diffuse pleural thickening is usually, but not inevitably, associated with heavy asbestos exposure, and its incidence increases with increasing time since first exposure. The pleural fibrosis is often progressive, resulting in restrictive lung defects, especially if the costophrenic angle is obliterated.
Pleural (with or without concurrent pulmonary) fibrosis can also occur with the use of ergot alkaloids (e.g., bromocriptine, pergolide, and methysergide)., It has been suggested that subjects with asbestos exposure may be more susceptible to bromocriptine-induced pleural fibrosis. Onset of dyspnea from ergot-induced pleural fibrosis is usually insidious and in the majority of cases presents at least 6 months after starting the medication. The pleural thickening is usually bilateral but can be unilateral, and may be associated with pleuritic pain. Constitutional symptoms and elevated serologic inflammatory markers have also been reported. In the case of bromocriptine, the fibrothorax will stop progressing on cessation of the drug use, and may regress, though complete resolution is rare. Corticosteroids are often administered, but their effectiveness has never been established. Pleural fibrosis is often bilateral (if due to systemic causes) and may be associated with concurrent peritoneal fibrosis.
Although pleural fibrosis is usually an undesirable event, it is commonly used therapeutically (pleurodesis) to control pleural effusions and pneumothoraces. Pleurodesis is the iatrogenic induction of pleural fibrosis, leading to symphysis of the visceral and parietal pleurae to obliterate the pleural space to prevent fluid or air reaccumulation. Interestingly, pleurodesis has no major impact on pulmonary function, even after decades. A retrospective review of young patients treated 22 to 35 years ago for spontaneous pneumothoraces showed that those who received talc pleurodesis (n = 80) had a higher incidence of pleural thickening on radiographs, but minimal restrictive changes in their lung function when compared with those treated by simple drainage (n = 34). Several small human and animal studies also revealed no significant impairment in lung volumes and gas exchange at rest or during exercise following pleurodesis. Such observations imply that, for a fibrothorax to be clinically significant, it must involve either very extensive pleural fibrosis (in excess of therapeutic pleurodesis) or concomitant parenchymal fibrosis.
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