PLEURISY or PLEURITIS. A medical term for inflam mation and the effects of inflammation affecting the pleura (see COELOM AND SEROUS MEMBRANES). Pleurisy may be induced mechanically, e.g., by a blow, but more commonly is the result of microbial infection whether conveyed directly by the blood (as in scarlatina) or extending to the serous membranes from an inflammatory focus in the lung or adjacent part.
The condition may be acute or chronic. In acute pleurisy the normal glistening appearance of the serous membrane is lost, it becomes injected with blood, roughened from the deposition of fibrin from the serum that exudes from the dilated and inflamed blood vessels and so long as the two surfaces are in contact occasions much pain from friction during respiration. The amount of serum poured out into the pleural cavity and the amount of fibrin formed vary within wide limits. The fluid may accumu late to such an extent that there is bulging outwards of the inter costal spaces and the lung is rendered airless and compressed at the back of the pleural cavity close to the vertebral column. The fibrin may form a thick white felty layer over the entire lung.
The subsequent history of a pleurisy varies. If the effusion of fluid causes respiratory or cardiac distress surgical removal (tho racentesis) of a portion of the fluid is necessary; lymphatic and venous drainage are effective in removing the remainder. There may then be complete recovery, the compressed lung resuming its function if it has not been left compressed too long. In other cases fibrous adhesions, formed by the same process as that which leads to scar tissue (see PATHOLOGY) bind the two layers of the pleura together over a greater or less extent of their surface. The condition is then one of chronic pleurisy and re crudescences of inflammation with local pain and effusion of fluid may occur. If the pleurisy arise by extension from a pul
monary, diaphragmatic, costal or pericardial focus of disease its character is determined by that of the primary focus. If tuber culous, tuberculous nodules are found in the thickened material covering and replacing the normal serous membrane ; if malignant disease the nodules are cancerous and the fluid often contains many red blood cells; while if the primary focus be that form of pneumonia which is caused by the pneumococcus and is charac terized by the local output of numerous leucocytes, the pleurisy will be similar and frequently purulent (see EMPYEMA).
The symptoms and signs of pleurisy present difficulty. Where the patient complains of a sharp pain in the side especially on drawing a deep breath, the normal resonant note on percussion of the chest is replaced by a dead, dull note, the breath sounds are barely audible and the ear applied to the chest detects a rubbing sound, a diagnosis of pleurisy is easy. But the relative infrequency of these phenomena and the very great frequency with which pleural adhesions, often of wide extent, are found in the post-mortem room without the slightest indication that the patient during life complained of symptoms such as the appear ances would seem to suggest, indicate that pleurisy is often symp tomless. The inference is that pleurisy is very common, but com paratively rarely calls for medical or surgical treatment.