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.

Source: National Institutes of Health