Gout is one of the most painful rheumatic diseases. It results from deposits of needle-like crystals of uric acid in connective tissue, in the joint space between two bones, or in both. These deposits lead to inflammatory arthritis, which causes swelling, redness, heat, pain, and stiffness in the joints. The term arthritis refers to more than 100 different rheumatic diseases that affect the joints, muscles, and bones, as well as other tissues and structures. Gout accounts for approximately 5 percent of all cases of arthritis.
Pseudogout is sometimes confused with gout because it produces similar symptoms of inflammation. However, in this condition, also called chondrocalcinosis, deposits are made up of calcium phosphate crystals, not uric acid. Therefore, pseudogout is treated somewhat differently.
Uric acid is a substance that results from the breakdown of purines, which are part of all human tissue and are found in many foods. Normally, uric acid is dissolved in the blood and passed through the kidneys into the urine, where it is eliminated. If the body increases its production of uric acid or if the kidneys do not eliminate enough uric acid from the body, levels of it build up in the blood (a condition called hyperuricemia).
Hyperuricemia also may result when a person eats too many high-purine foods, such as liver, dried beans and peas, anchovies, and gravies. Hyperuricemia is not a disease and by itself is not dangerous. However, if excess uric acid crystals form as a result of hyperuricemia, gout can develop. The excess crystals build up in the joint spaces, causing inflammation. Deposits of uric acid, called tophi (singular: tophus), can appear as lumps under the skin around the joints and at the rim of the ear. In addition, uric acid crystals can collect in the kidneys and cause kidney stones.
For many people, gout initially affects the joints in the big toe. Sometime during the course of the disease, gout will affect the big toe in about 75 percent of patients. It also can affect the instep, ankles, heels, knees, wrists, fingers, and elbows. The disease can progress through four stages: