Why does pleural effusion cause pain in the back

Condition analysis:
The pleura is a thin membrane that lines the inside of the chest wall and covers the lungs. There is normally a tiny amount of fluid between the two layers of pleura. This acts like lubricating oil between the lungs and the chest wall as they move when you breathe. A pleural effusion develops when this fluid builds up and separates the lung from the chest wall.

Instructions:
Treating the underlying cause
A major part of treatment is usually directed to the underlying cause of the build-up of fluid between the lung and the chest wall (pleural effusion). For example, medicines called antibiotics for lung infection (pneumonia), chemotherapy or radiotherapy for cancers, etc. Therefore, treatment can vary greatly, depending on the cause of the effusion. If the underlying cause can be successfully treated then there is a good chance that the pleural effusion will go away for good. If the underlying cause cannot be treated, or can only be partially treated, the effusion may return if it is cleared (drained).

Treating the effusion itself
Small effusions that cause no symptoms, or only mild symptoms, may just be left and 'observed'. Treatment is usually only needed if the effusion causes symptoms such as breathlessness.

A large pleural effusion that makes you breathless can be drained. This is called a pleural fluid aspiration or pleural tap. It is usually done by inserting a needle or tube through the chest wall. A local anaesthetic is injected into the skin and chest wall first to make the procedure painless. This may be a 'one-off' procedure to relieve symptoms.