Pleuritis is the term for inflammation of the pleura, the double layered lining around the lungs. Although the term pleuritis and pleurisy is used synonymously, pleurisy actually refers to any pain from the pleura (pleuritic pain). The outer pleural layer is known as the parietal pleura and lines the inside of the chest cavity around the lung. The inner pleural layer is attached to the lungs and is known as the visceral pleura. The pleural cavity is the space between the two pleural layers and it contains approximately 10 to 20ml of thin serous fluid known as the pleural fluid. This serves as a lubricant when the two layers rub against each other during lung expansion and contraction in respiration.
When the pleural lining is irritated, it swells, secretes larger amounts of pleural fluid and elicits pain, particularly the parietal pleura. The composition of the pleural fluid may change and depending on the cause, it can increase to an extent that affects the expansion of the lungs during respiration. This excess pleural fluid is known as a pleural effusion, or simply fluid around the lungs. This should be differentiated from fluid in the lungs which is pulmonary edema. The close proximity to other structures and organs in the chest cavity means that pleurisy may arise secondary to various other conditions, especially those that affect the heart and its lining (pericardium).
Pain emanating from the pleura is a common feature of most pleural disorders, even conditions that do not cause pleural inflammation (pleuritis). When the pleura are inflamed and rub against each other, it elicits pain. Pleuritic pain is described as a sharp stabbing that is most prominent during inhalation, deep breathing and coughing.
Pleuritic pain is often thought of as chest wall pain that is exacerbated during inhalation. However, the pain may radiate or refer to surrounding areas.
- If the parietal pleura lying in the area of the upper six ribs is inflamed, it causes localized pain (upper chest pain).
- When the pleura behind the lower ribs and outer parts of the diaphragm are inflamed, the pain may be referred to the upper abdomen.
- Inflammation of the pleura around the central diaphragm may refer pain to the neck or shoulder tip due to the course of the phrenic nerve.
Pleural disorders presenting with an effusion (fluid around the lungs) is less likely to cause this typical pain given that there is sufficient lubrication between the two pleural layers. However pain is a feature of the the inflammatory process and may still be present with a pleural effusion although the aggravation associated with breathing and coughing may not be as prominent.