Several classification systems have been used to describe diabetes mellitus. A human classification system revised in 1997 divides the disease into three types: type 1 (previously insulin-dependent or juvenile-onset diabetes mellitus), type 2 (previously non–insulin-dependent or adult-onset diabetes mellitus), and other specific types of diabetes mellitus (previously secondary or type 3 diabetes mellitus).
The most commonly recognized form in dogs is type 1 (insulin-dependent diabetes mellitus). Dogs with the insulin-dependent form of the disease require daily insulin injections to control disease signs and delay the multisystemic disorders associated with the diabetic disease process.
Untreated dogs commonly display severe weight loss, polydipsia, and polyuria. They may experience dehydration and severe metabolic and electrolyte abnormalities if severe ketoacidosis develops. Untreated or improperly managed diabetic dogs suffer a decreased quality of life, and most die without appropriate therapy and monitoring.