Slight thickening of the pleura bilaterally is caused by increased pleural exudate due to lesions in the pleura or other causes, resulting in fibrosis of the pleura, which causes thickening of the pleura. The common causes of bilateral pleural thickening are. 1. Tuberculous pleurisy: infection of the pleura by Mycobacterium tuberculosis can cause limited pleural adhesion and thickening. 2. pyothorax: infection of pleura by purulent pathogens can cause pleural thickening in early stage. 3. metastatic malignant tumor of pleura: after tumor cells invade bilateral pleura, it will produce exudative pleural effusion, secondary to pleural thickening. 4. Pneumoconiosis: inhalation of large amount of dust due to poor environment, which is deposited on the surface of pleura and can lead to bilateral pleural thickening. There are other reasons for bilateral pleural thickening symptoms, you need to go to the hospital in time to check, identify the cause of the disease and then actively targeted treatment.