Diabetes Mellitus, Type 2
Updated: Jul 2, 2009
Introduction
Background
Until recently, type 2 diabetes mellitus was almost exclusively a disease of adults. Coinciding with the increasing prevalence of obesity among American children, the incidence of type 2 diabetes in children and adolescents has markedly increased to the point that it accounts for as many as one third of all the new cases of diabetes diagnosed in adolescents. This trend is particularly pronounced in minority racial and ethnic groups.
Pathophysiology
In individuals without diabetes, approximately 50% of their total daily insulin is secreted during basal periods to suppress lipolysis, proteolysis, and glycogenolysis. In response to a meal, rapid insulin secretion (also called first-phase insulin secretion) ensues. This secretion facilitates the peripheral utilization of the prandial nutrient load, suppresses hepatic glucose production, and limits postprandial elevations in glucose levels. The second phase of insulin secretion follows and is sustained until normoglycemia is restored.
Type 2 diabetes spans a continuum from impaired glucose tolerance and impaired fasting glucose to frank diabetes resulting from progressive deterioration of both insulin secretion and action. Although the first phase of insulin response is markedly reduced early in the course of the disease, ongoing disorganized insulin secretion associated with deterioration of peripheral insulin action occurs during the progression from normal to impaired glucose tolerance to frank diabetes.
In parallel, as a result of decreased insulin sensitivity in the liver, endogenous glucose output increase adds to the already hyperglycemic milieu, worsening both peripheral insulin resistance and beta-cell function. Failure of the beta cell to keep up with the peripheral insulin resistance is the basis for the progression from impaired glucose tolerance to overt clinical type 2 diabetes. A longitudinal study demonstrated that, during the transition between normal glucose tolerance to diabetes, 31% of the person's insulin-mediated glucose disposal capacity is lost, whereas 78% of the acute insulin response is also lost during the same period.
Frequency
United States
Although type 2 diabetes is widely diagnosed in adults, its frequency has increased markedly in the pediatric age group during the past decade. Type 2 diabetes represents 8-45% of all new cases of diabetes reported among children and adolescents. Most pediatric patients in whom type 2 diabetes is diagnosed belong to minority communities.
International
An increased prevalence of type 2 diabetes has also been recognized in countries other than the United States, including Japan, where the incidence has doubled during the past 2 decades. In the Chinese, Taiwanese, and indigenous people of Australia, a trend for type 2 diabetes to occur at younger ages than before has also been recognized.
Mortality/Morbidity
Overall, morbidity and mortality associated with type 2 diabetes are related to short- and long-term complications.
- According to a follow-up study of Pima Indians in whom type 2 diabetes was diagnosed before the age of 20 years, the incidence of nephropathy was not significantly different from that in patients with adult-onset diabetes. This result indicated a high risk of end-stage renal disease in the third and fourth decades of life.
- In a comparative study among youths with type 1 and type 2 diabetes, the cumulative incidence of nephropathy was higher than it was in those with type 1 diabetes. Nephropathy also appeared earlier in type 2 than in type 1 diabetes.
- The risk of retinopathy is lower in patients with youth-onset type 2 diabetes than in those with adult-onset diabetes.
Race
Type 2 diabetes primarily affects minority populations.
- From 1967-1976 to 1987-1996, the prevalence of type 2 diabetes increased 6-fold in Pima Indian adolescents and appeared for the first time in children and adolescents younger than 15 years.
- Similar increases in prevalence were observed among Japanese, Asian-American, and African-American children. In several clinics across the United States, pediatric patients with a diagnosis of type 2 diabetes were from minority ethnic groups (African-American, Asian, and Hispanic groups).
Sex
The prevalence of type 2 diabetes in the pediatric population is higher among girls than boys, just as it is higher among women than men.
Age
The mean age of onset of type 2 diabetes is 12-16 years; this period coincides with puberty, when a physiologic state of insulin resistance develops. In this physiologic state, type 2 diabetes develops only if inadequate beta-cell function is associated with other risk factors (eg, obesity).
Clinical
History
At the time of diagnosis, determine whether a patient has type 1 or type 2 diabetes because patients with type 1 diabetes are totally dependent on exogenous insulin administration for survival, whereas patients with type 2 diabetes do not necessarily require exogenous insulin to survive.
- Because of the increasing prevalence of obesity in the pediatric population, the percentage of immune-mediated diabetes in overweight or obese patients is increasing, rendering the distinction between type 1 and type 2 diagnoses difficult at times. Blood glucose monitoring is required regardless of the type of diabetes, and treatment with insulin should be started when indicated.
- The onset of type 2 diabetes is usually slow and insidious; it most often occurs in overweight or obese patients from a minority group.
- Patients with type 2 diabetes often have signs of insulin resistance, such as hypertension or acanthosis nigricans.
- A strong family history for the disease is usually reported among affected youth. The families of adolescents with type 2 diabetes also often have lifestyle risk factors leading to obesity.
- Children with diabetes type 2 are more likely to report a family history of cardiovascular disease.
- Autoimmune markers are usually negative.
- Type 1 diabetes occurs in people of all races; its onset is typically acute and severe.
- Patients with type 1 diabetes are often lean and do not show manifestations of insulin resistance.
- Autoimmunity is present in diabetes type 1.
Physical
- Obesity is strongly associated with type 2 diabetes in children and adolescents. Eighty-five percent of children with type 2 diabetes are either overweight or obese (defined as at or above the 85th percentile of the sex-specific body mass index [BMI] for age-based growth charts).
- Acanthosis nigricans, a marker of insulin resistance, is a velvety hyperpigmented thickening of the skin; it is frequently seen on the nape of the neck and in intertriginous areas; it is found in as many as 90% of children with type 2 diabetes.
- Polycystic ovarian syndrome (PCOS) is a reproductive disorder commonly seen in young women with acanthosis nigricans. It is characterized by hyperandrogenism and chronic anovulation. The role of insulin resistance in the etiology of PCOS has been extensively studied, and medications that decrease insulin resistance and/or hyperinsulinemia in women with this syndrome often attenuate the hyperandrogenism and metabolic abnormalities.
- Hypertension may occur in children with type 2 diabetes. The risk of macrovascular and microvascular diabetic complications is positively associated with elevated systolic blood pressure.
- Ophthalmologic examination should be performed at or shortly after diagnosis to detect incipient retinopathy.
Causes
The major risk factors for type 2 diabetes in youths are the following:
- Obesity and inactivity, which are important contributors to insulin resistance
- Native American, Hispanic, Asian, and Pacific Islander descent
- Family history of type 2 diabetes
- Age of 12-16 years, the mean age at the onset of type 2 diabetes in youths (This age coincides with relative insulin resistance that occurs during pubertal development.)
- Low birth weight
