[Pleural diseases: an unusual cause of cough]

The parietal pleura contains myelinated sensitive nerve fibers as well as mechanoreceptors which coordinate the breathing muscles. The small volume of fluid within the pleural space is in dynamic balance: hydrostatic and colloid-osmotic pressures maintain a constant flow of fluid from the parietal to the visceral pleura, which turns into pleural effusion under pathological conditions. Separation of transudate from exudate is best done by calculation of the protein and LDH ratios in the pleural fluid and in serum. Transudates of cardiac origin are due to congestive left heart failure alone. In detecting subpulmonary pleural effusion, ultrasonography is more accurate than X-ray in lateral decubitus. Pleural exudate is investigated by chemical, microbiological and cytological examination of the fluid, complemented by pleural biopsy, fibre bronchoscopy and thoracoscopy. In this way less than 10% of pleural effusions remain unexplained.