pleurisy

Inflammation of the pleura, the thin, secretory membrane that covers the lungs and lines the space in which they rest. Pleurisy is nearly always due to bacterial or viral infection, but may also be a complication of other diseases.

Normally the two lung surfaces move easily on one another, lubricated by small quantities of fluid. When the pleura is inflamed, the surfaces may dry up or stick together, making breathing difficult and painful. Alternatively, a large volume of fluid may collect in the pleural cavity, the space between the two surfaces, and pus may accumulate.