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Oxford University Hospitals NHS Foundation Trust
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Inflammatory diseases

A normal knee joint with the right amount of fluidWhat is inflammation?

Inflammation is normally helpful.

At times of infection, trauma, or other causes of harm to the body, inflammation plays a very important role in protecting the injured tissue from further infection and starting the healing process. It does this by increasing blood flow to the damaged tissue to both deliver important blood cells and proteins and wash away unwanted breakdown products or debris.

This process of inflammation is best seen in the skin. Inflammation appears red and hot because of increased blood flow and the intense activity of cells. These cells leak into the skin tissues along with fluid and proteins from the blood to produce swelling. Sometimes, as with inflammation of infection, high collections of cells appear as pus. The same process occurs in all parts of the body whenever injured.

What is an inflammatory disease?

In an inflammatory disease, inflammation occurs by mistake.

Increased blood flow and cells arrive at a given site, causing heat, swelling, pain and loss of function, but there is no infection and no trauma has occured. Attacking the body without an external insult in this way is called autoimmunity.

A sore, swollen knee joint of an arthritis suffererThis is what happens in arthritis. The tissue that swells is the lining of the joint and increased fluid is produced. Together these make the joint swollen, painful and stiff to move. There is also loss of function - for example, a swollen knee makes it difficult to walk.

Inflammation can also cause:

  • Enlargement and loss of function of the kidney (as in SLE)
  • Swelling and loss of function of blood vessels (as in Vasculitis)
  • Swelling and loss of function of muscles (as in Juvenile Dermatomyositis)

…in fact any organ can be affected in this way.

What are the long term effects?

The overall effect of this inflammation depends on how long it lasts.

Short periods of inflammation, such as with an allergic reaction or reactive arthritis, are generally fully resolved and leave no long term problems. 

Inflammation that lasts several months or years or is particularly severe may cause lasting damage to the affected area or organ (for example, leading to deformed joints). This is what happens in arthritis.