Knowledge of the usual course of a disease from its onset and pretreatment phase through to its final outcome is important for several reasons. It enables predictions to be made about a patient’s likely recovery or degree of eventual disability, i.e. the prognosis. It also helps in judging whether improvements in a patient’s condition are due to treatment or to natural remission. Many chronic diseases progress by a series of exacerbations, remissions and relapses, and improvements cannot with certainty be ascribed to any treatment that is being given. The patient may have improved even without the treatment. Different disease subgroups may be differentiated by different natural histories. For example, RA typically has an insidious onset, but if there is a sudden onset of multi-joint inflammation the prognosis is better. Furthermore, some twothirds of RA patients will have such a slowly
progressive disease that they can expect little disablement within a normal lifespan.