Gout is a condition caused by the collection of needle-like uric acid crystals in one or more joints. Uric acid is a waste product made naturally by the body. Increased levels of uric acid occur following the breakdown of a substance called purines. These are found naturally in DNA, the building blocks of our cells, and in many foods . Foods high in purines include sardines, anchovies, mussels, yeast extracts such as Marmite, beer and game meat. The body gets rid of most of its uric acid via the kidneys in the urine and also from the bowel in the faeces.
In people with gout the uric acid levels build up and can crystallise in the joints. This may be due to:
- the body making more uric acid
- more uric acid products being consumed in the diet ( usually by eating foods high in purines)
- or if the body cannot get rid of the uric acid it makes.
This build up of uric acid in the joint causes inflammation, swelling, and severe pain. The most frequently affected joint is the big toe. Other joints that are often affected include the hands, wrists, knees, and feet.
Although certain foods are high in purines, it is very rare that someone could consume enough purines in their diet alone to cause the uric acid levels to rise to significant levels. It is thought that people who are prone to gout tend to excrete less uric acid via their kidneys which then cause the uric acid levels to rise. This makes them more sensitive to any condition that causes uric acid levels to rise including the foods they eat. Although the majority of people with gout have raised uric acid levels, sometimes people with normal uric acid levels can have gout attacks. This however is rare. It is also important to remember that the majority of people with raised uric acid levels will not develop gout. However, if uric acid levels are raised then gout theoretically can develop.
Therefore there are certain risk factors that can make someone more prone to gout. For example, gout develops more often in men than in women and is more common in adults. In addition, people with type 2 diabetes, obesity, sickle cell anaemia, and kidney disease have an increased risk of developing gout. Drugs such as cyclosporine, thiazide diuretics, and salicylates (aspirin) can interfere with uric acid excretion as can an excess of alcohol, which itself is high in purine content. In rare instances, a person may inherit a decreased ability to breakdown purines and so be more likely to develop gout. It has also been found that having low levels of vitamin C in your diet or consuming too much fructose can increase the risk of gout. Fructose is the only carbohydrate known to increase uric acid levels and is found in high concentrations in sugar-sweetened soft drinks.
What is a Gout Attack?
An attack of gout is usually caused when the uric acid crystals deposit themselves in the joints and tissues. This normally causes sudden pain, redness and swelling in a joint. It is usually very painful, but self-limiting, and will normally resolve by itself in about a week. However, some attacks may not be as severe as this and can sometimes make the diagnosis difficult if they lack the classical symptoms of a gout attack.
Gout must be distinguished from conditions that can cause similar symptoms:
- Pseudogout, a condition caused by calcium pyrophosphate crystals
- Septic arthritis (caused by an infection in a joint)
- Rheumatoid arthritis (an autoimmune arthritis)
- Osteoarthritis (wear and tear)
The treatments of these conditions are different to those used in gout.
A gout attack may be a one off occurrence or the attacks may be recurrent. However repeat attacks may not occur for years after the initial one. Some people may be unlucky and have recurrent attacks on a regular basis. Repeat attacks tend to be more severe and affect more joints. It is more common to get repeat attacks as time goes on as the uric acid levels gradually increase.
The uric acid crystals may also deposit in the kidneys causing kidney stones and more rarely kidney damage. Occasionally, in those with persistently high levels of uric acid the crystals build up over years and form deposits called tophi. These can build up in the joints and soft tissues and can cause visible nodules through the skin that look chalky white. They are harmless, however can be painful at particular sites. Tophi caused by raised uric acid levels can also deposit in the joint themselves and if left untreated cause permanent damage to the joint. This however takes several years and is therefore uncommon as gout is normally treated before this complication develops.