Gout is one form of arthritis. It can be divided into two categories, either primary or secondary, depending on the cause. It is sometimes confused with pseudogout, which often affects the knee joints.
There are different stages of gout. In its early stage, attacks occur a few times each year and last for several days. In its advanced stages, tophi (uric-crystal deposits) can begin to collect under the skin and become swollen and painful during an attack.