Pain in multiple joints

[Justin Bieber]

Joints may simply be painful (arthralgia) or also inflamed (arthritis). Joint inflammation is usually accompanied by warmth, swelling (due to intra-articular fluid, or effusion), and uncommonly erythema. Pain may occur only with use or also at rest. Sometimes what is described by patients as joint pain can have an extra-articular source (eg, a periarticular structure or bone).
Polyarticular pain (polyarthralgia) involves multiple joints (pain in a single joint is discussed elsewhere). Polyarticular joint disorders may affect different joints at different times. When multiple joints are affected, the following distinction can be useful in differentiating among different disorders, particularly arthritides:

Oligoarticular: Involving ≤ 4 joints
Polyarticular: Involving gt; 4 joints