The intercostal space is the gap between the ribs, and pleural thickening in the left intercostal space may be caused by inflammation, tumor, rheumatic immune disease, etc., and pathological changes such as localized fibrosis of the pleura appear. 1. Inflammation: including chronic tuberculous pleuritis, chronic purulent pleuritis and other diseases, inflammatory exudate repeatedly stimulate the pleura, which will lead to pleural thickening and fever, chest pain and other manifestations, and need to be timely for the cause of treatment. 2. Tumors: including malignant mesothelioma, breast cancer pleural metastasis, lung cancer, etc., which will lead to pleural thickening, accompanied by fever, emaciation and other manifestations. 3. Rheumatic immune diseases: Rheumatic immune diseases that may lead to pleural thickening include systemic lupus erythematosus, rheumatic pleurisy, etc., which may be accompanied by generalized pain and other manifestations. If you suspect any of the above diseases, it is recommended that you go to the hospital in time.