Causes of pleurisy

Pleurisy is inflammation of the pleura. It's usuallycaused by another condition, such as an infection, but sometimes no cause can be identified.

The pleura are two thin sheets of tissuethat separate the lungs and ribcage. One is attached to the ribcage and the other is attached to the lungs.

Between the pleural sheets is a thin layer of liquid that lubricates the pleura, helping to reducefriction when you breathe in and out.

When there's inflammation, the surfaces of the two layers can become rough and the fluid can become sticky. This can cause the layers to rub together, resulting in pain and discomfort.

Infection

An infection is the most common cause of pleurisy.Any type of infection has the potential to spread to the pleura, but viral infections are usually responsible.

Viruses known tocausepleurisy include:

• the influenza (flu) virus
• the Epstein-Barr virus whichcauses glandular fever
• cytomegalovirus (CMV) a common virus found in most people, which doesn't usually cause any noticeable symptoms
• parainfluenza the virus that causes the childhood condition croup

In some cases, pleurisy is caused by bacteria, such as:

• streptococcal bacteria often associated with pneumonia , throat infections and some types of skin infections, such as impetigo and cellulitis
• staphylococcal bacteria often associated with skin infections, food poisoning and, more seriously, blood poisoning (sepsis)

Meticillin-resistant Staphylococcus aureus (MRSA) can cause pleurisy, especially inhospital patients. MRSA is a type of bacteriawith a resistance to a number of commonly used antibiotics.

Other causes

Other possible causes of pleurisy include:

• injury if the ribs are bruised or fractured, the pleura can become inflamed
• pulmonary embolism a blood clot developing inside the lungs
• sickle cell anaemia a blood disorder that usually affectspeople of African or Caribbean descent
• chemotherapy and radiotherapy
• HIV or AIDS
• lung cancer
• mesothelioma a type of cancer caused by inhaling asbestos

Autoimmune conditions, such as rheumatoid arthritis and lupus , are other possible causes of pleurisy. In these conditions, something goes wrong with the immune system (the bodys natural defence against infection and illness)and it begins to attack healthy tissue.