Diagnosis, Classification, and Pathogenesis of Diabetes Mellitus

Diabetes mellitus is a metabolic disorder that is characterized by inappropriate hyperglycemia andis associated with both acute and chronic complications. Currently, diabetes mellitus is diagnosed byblood or plasma glucose levels. A random plasma glucose level ≥ 200 mg/dL in an individual withclassic symptoms is sufficient to make the diagnosis. Otherwise, a fasting plasma glucose level ≥ 126mg/dL or a 2-hour plasma glucose level ≥ 200 mg/dL after an oral glucose challenge of 75 g on 2occasions is sufficient evidence upon which to diagnose diabetes mellitus. The major types of diabetesmellitus are type 1 diabetes (insulin deficient) and type 2 diabetes (combination of insulin resistanceand insulin deficiency). In both types, there is a genetic predisposition as well as environmental factorsthat contribute to the expression of the genetic predisposition. In type 1 diabetes, the primary abnormalityis extensive deficiency of beta cell function. In type 2 diabetes, insulin resistance occurs,and the marked compensatory increases in insulin secretion necessary to maintain normal glucose tolerancecannot be achieved or maintained. As beta cell function continues to decrease, the individualprogresses from normal glucose tolerance to impaired glucose tolerance to diabetes with primarilypostprandial hyperglycemia to diabetes with fasting hyperglycemia. Drugs can cause diabetes by interferingwith beta cell insulin secretion, by increasing insulin resistance, or by a combination of both.Atypical antipsychotic drugs have been reported to cause diabetic ketoacidosis, obesity and insulinresistance, type 2 diabetes, and hypertriglyceridemia. A monitoring system should be in place in patientsstarted on treatment with these agents to detect metabolic abnormalities as they are evolving sothat adequate and timely treatment can be initiated.